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service manual nellcor® n-200 pulse oximeter

1. 2 2 3 DPG or fetal hemoglobin In general calculated saturation values are not reliable as correlative measurements check to see that the calculations have been corrected for relevant variables For more information see Section 3 1 4 Accuracy can be affected by incorrect sensor application or use significant levels of dysfunctional hemoglobins intravascular dyes bright light excessive patient movement venous pulsations electrosurgical interference and placement of a sensor on an extremity that has a blood pressure cuff arterial catheter or intravascular line Observe all instructions warnings and cautions in the N 200 Operator s Manual and in the directions for sensor use The oxygen saturation measurement of the N 200 does not correlate with a value measured by a laboratory CO Oximeter Fractional measurements have not been converted to functional measurements before the comparison was made The NELLCOR N 200 like other two wavelength oximeters measures functional saturation Multi wavelength oximeters such as the IL282 CO Oximeter and Corning oximeters measure fractional saturation Fractional measure ments must be converted to functional measurements for comparison The equation used to make this conversion can be found in Section of the N 200 Operator s Manual The OXYGEN SATURATION display is erratic and the ECG LOST display is flashing Excessive patient motion has caused the ECG electrodes to become
2. B Blown AC fuse and battery discharged Refer to Section 4 4 1 Blown AC and battery fuses Refer to Sections 4 4 1 and 4 3 5 Failure of the switching circuitry on the charger board Refer to Sections 5 3 4 and 3 7 Power supply failure Refer to Sections 5 3 1 and 3 6 Logic failure on the processor board Refer to Sections 5 4 and 3 4 Failure of battery charger circuit on the charger board Refer to Sections 5 3 3 and 3 7 2 Battery failure Refer to Sections 5 3 and 4 3 5 Blown battery fuse Refer to Section 4 3 5 Blown AC fuse Refer to Section 4 4 1 AC rectifier failure on the charger board Refer to Sections 5 3 3 and 3 7 AC rectifier filter failure on power supply Refer to Sections 5 3 1 and 3 6 18 V power supplies out of spec Refer to A Failure of microprocessor logic on processor board including the micro processor ROM RAM and associated circuitry Refer to Sections 5 4 and 3 4 5 V power supply out of spec Refer to Sections 5 3 1 and 3 6 Failure of switching circuit on charger board Refer to Sections 5 3 4 and 3 7 10 INSTRUMENT OPERATES DISPLAY SHOWS Err 1 INSTRUMENT OPERATES DISPLAY SHOWS Err 2 INSTRUMENT OPERATES DISPLAY SHOWS Err 3 INSTRUMENT OPERATES DISPLAY SHOWS Err 4 INSTRUMENT OPERATES DISPLAY SHOWS Err 5 INSTRUMENT OPERATES DISPLAY SHOWS Err 6 Probable Diagnosis A Failure
3. use C LOCK ECG synchronization test the instrument on yourself or another patient try the nasal OXISENSOR R 15 Excessive patient motion is making it difficult for the instrument to find the actual pulse pattern use C LOCK ECG synchronization set the N 200 for Mode 3 refer to Operator s Manual Patient module cannot be connected to the instrument Incorrect type of patient module is being used Use a NELLCOR N 200 series patient module The connector pins are bent Straighten them carefully or replace the patient module the plug is internally sealed and should not be disassembled Saturation and or pulse rate display are changing rapidly and pulse amplitude indicator is erratic Excessive patient motion is making it difficult for the instrument to find a pulse pattern use C LOCK ECG synchronization or if possible ask the patient to remain still or check whether the sensor is securely applied and replace it if necessary or 10 11 use a type of sensor that tolerates more patient motion or move the sensor to a site with less movement or use Mode 3 if appropriate Refer to the N 200 operator s manual An electrocautery unit is interfering with performance the ECU cable and N 200 patient module are too close to each other Move them as far apart as possible the sensor is too close to the ground pad or electrocautery site Move sensor to a different site if
4. 3 5 watchdog timer circuit testing 5 4
5. Channel 1 100 mV div AC Coupling Sweep Rate 50 ms div Trigger Channel 1 Connect the OSCILLOSCOPE ground to AGND on the Processor PCB Connect the OSCILLOSCOPE Channel 1 lead to CR1 cathode bar on the Power Supply PCB The lower frequency noise must not exceed 100 mV p p Connect the OSCILLOSCOPE Channel 1 lead to FB2 on the Power Supply PCB The lower frequency noise must not exceed 100 mV p p Connect the OSCILLOSCOPE Channel 1 lead to pin E5 on the Power Supply PCB The lower frequency noise must not exceed 100 mV p p Remove the all test equipment from the N 200 and place the ON STDBY switch in the STDBY position PROCESSOR PCB TESTS The following tests are designed to test processor PCB operation The following circuits will be tested in this section and adjustment details explained as necessary 1 2 10 Processor PCB Voltage Regulation Calibration Resistor Determination LED Intensity Control Input Amplifier INAMP automatic gain Sync Detector Alignment IR Channel Gain RED Channel Gain ECG Processor A D D A Alignment Clock Calendar Lithium Battery Prepare the N 200 for testing by performing the following procedures 1 2 Place the ON STDBY switch to the STDBY position Place a jumper wire in location W3 on the Processor PCB WARNING the jumper must be removed at the end of the Processor PCB tests Failure to remove the jumper could allow the operator to accidentally int
6. NO ANALOG OR DIGITAL OUTPUTS A AC power disconnected B Picofuse blown on mother PCB Refer to Section 3 8 1 C Faulty transformer Refer to Section 3 8 D Digital circuitry on upper or lower daughter boards Refer to Section 3 8 2 2 FULL SCALE AND ZERO SWITCHES Phototransistor on mother PCB defective WORK BUT NO ANALOG OUTPUTS Refer to Section 3 8 1 MONITOR INFORMATION DOES NOT LED on monitor power supply board APPEAR ON DIGITAL OUTPUTS defective Refer to Section 3 6 3 TREND EVENT FUNCTIONS A AC power disconnected INOPERATIVE EXTERNAL LED on mother PCB defective Refer to ECG INOPERATIVE ADULT Section 3 8 1 NEONATE ALARM SWITCH Phototransistor on power supply PCB INOPERATIVE defective Refer to Section 3 6 4 NOORINCORRECT DIGITAL OUTPUT A Baud rate mismatch between power base and output device Refer to N 200 Operator s Manual 4 3 MONITOR DISASSEMBLY AND REASSEMBLY Unless otherwise noted the method used for reassembly of the instrument or one of its subas semblies is the reverse of that used for disassembly 4 3 1 Top Cover Removal Remove AC power cord from the instrument Disconnect the powerbase Place the instrument top down on a flat work surface Remove the four Phillips head screws from the bottom of the instru ment taking care not to lose washers Turn the instrument over with the front panel facing you Lift off the top cover and place it on your left as shown in Figu
7. Use 1 V mV ECG analog output or defib sync pulse wave AC power to the powerbase may have been interrupted this applies only if the ECG signal is being supplied via the rear panel connector When EGG is connected pulse rate is displayed but saturation is not The patient s perfusion may be inadequate check the condition of the patient test the instrument on yourself or another patient try the nasal OXISENSOR R 15 The pulse rate displayed by the N 200 does not correlate with that of the ECG monitor Excessive patient motion is making it difficult for the instrument to find a pulse pattern use C LOCK ECG synchronization or 4 4 12 13 14 if possible ask the patient to remain still check whether the sensor is securely applied and replace it if necessary or use a type of sensor that tolerates more patient motion or move the sensor to a site with less movement or use Mode 3 if appropriate refer to the N 200 Operator s Manual The patient has a pronounced dicrotic notch which causes the pulse rate to double Try another sensor site An artifact is present on the ECG monitor Refer to the manual for that monitor An electrocautery unit is interfering refer to item number 8 Oxygen saturation measurement does not correlate with the value calculated from a blood gas determination The calculation has not been correctly adjusted for the effects of pH temperature
8. the method used for reassembly of the instrument or one of its subassemblies is the reverse of that used for disassembly 4 4 1 AC Fuse Replacement Fuses are contained inside a door above the AC power inlet on the back of the powerbase To gain access unplug the AC cord from the back of the powerbase and open the door by prying the top edge with a small flat blade screwdriver 4 14 Pull out the fuse holder on the right side to gain access to the fuse The holder contains 230 0 5 slo blow fuse Replace the fuse only with the same type and rating Replace the fuse holder by first making sure that the arrow on the holder points to the right and then pressing it into place A removable barrel can be set to either 115 V or 230 V positions If the barrel comes out of its holder be sure that it is replaced so that one of the 115 V settings United States units is exposed to view Close the fuse door by exerting firm pressure against the door 4 4 2 Powerbase Disassembly The powerbase is disassembled by removing the four Phillips nhead screws from the bottom of the unit With the unit upright on the bench lift off the top cover All electronics are contained in the bottom portion of the powerbase The solder side of the upper daughter PCB is exposed 4 4 3 PCB Removal The mother PCB is mounted vertically at the front of the unit The upper middle and lower daugh ter PCBs are mounted horizontally and mated to the mother
9. voltage for voltage regulator VR1 Current sensing resistor R15 provides current limiting through Q2 and Q3 cutting output voltage when current draw increases above 375 mA Trimmer potenti ometer R12 adjusts the nominal battery charging voltage to 7 1 V at TP5 Diode 9 prevents back discharge through the regulating circuit when AC power is removed With AC power disconnected battery voltage can vary between 6 6 V and 5 6 V 3 8 POWERBASE powerbase contains electronics for data communications for the 200 It is composed of a mother PCB and three daughter PCBs 3 8 1 Mother PCB The mother board is shown in the SCHEMATIC MOTHER PCB POWERBASE The mother board provides power for the rest of the powerbase electronics Bridge rectifier U2 charges filter capacitor C1 The AC voltage supplied at AC is typically 7 5 V RMS Voltage regu lator U3 and current booster Q1 form a linear regulator that lowers the rectified AC voltage to 5 V Portions of the powerbase analog circuitry require 15 V power DC DC converter U1 derives these voltages from the 5 V supply U4 and U5 regulate these voltages down to 12 V for use in the RS232 serial port Diode CR1 and phototransistor Q2 form one half powerbase side of the powerbase monitor opti cal link 3 8 2 Upper and Lower Daughter PCBs The upper and lower daughter PCBs comprise the digital portion of the powerbase electronics 3 8 2 1 Upper Daughter PCB In the upper daught
10. 3 1 3 1 1 C LOCK ECG Synchronization 3 1 2 Automatic Calibration 3 2 3 1 3 Functional vs Fractional Saturation 3 2 3 1 4 Measured vs Calculated Saturation 3 2 CIRCUIT LEVEL DESCRIPTION PATIENT MODULE 3 3 PROCESSOR PCB 3 4 3 4 1 Digital Section 3 4 3 4 1 1 Microprocessor Subsection 3 4 3 4 1 2 Memory Map 3 5 3 4 1 3 Wait State Generator 3 4 1 4 Clock Generator 3 5 3 4 1 5 Timer Circuits and UART 3 5 3 4 1 6 Pattern Generator 3 6 3 4 2 Analog Front End and LED Current Drive 3 4 2 1 Main Analog Signal Flow 3 6 3 6 3 4 2 2 Sync Detector 3 4 2 3 Demultiplexer 3 4 2 4 Logic Flags 3 7 3 7 3 4 2 5 LED Drive Circuitry 3 4 3 ECG Front End 3 4 3 1 Active Filters 3 8 3 4 3 2 Offset Amplifier 3 8 3 4 3 3 Detached Lead Indicator 3 4 3 4 Power Line Frequency Sensing 3 9 3 4 4 A D D A Subsection 3 9 3 4 4 1 A D Conversion 3 4 4 2 D A Conversion 3 10 3 4 5 Timing and Control 3 10 3 4 5 1 Polled Processor Flags 3 10 3 4 5 2 Interrupt Processor Flags 3 11 FRONT PANEL DISPLAY 3 11 3 5 1 Driver PCB 3 11 3 5 1 1 Digit and Bargraph Drivers 3 12 3 5 1 2 Lightbar Drivers 3 12 3 5 1 3 Front Panel Controls 3 12 3 5 1 4 Power Up Display Element Test 3 13 3 5 1 5 Sp
11. PCB The driver circuit board is shown on SCHEMATIC DRIVER PCB Refer to this schematic in the following discussion During power up CR2 R10 and C11 provide a short duration reset pulse to all latches on the driver board This reset pulse clears all front panel display elements Two different mechanisms are used to drive the display bargraph drivers drivers for the lightbars used with other front panel indicators such as PULSE SEARCH and AUDIO ALARM OFF 3 5 1 1 Digit and Bargraph Drivers A total of 8 components comprise the digit and bargraph displays DIGIT O through DIGIT 5 BARGRAPH BARGRAPH 1 The drive signals for these displays are multiplexed Latch U12 and decoder U13 are used to select which digit or bargraph to update Latch U10 and driver U11 determine which segments within the selected digit or bargraph are illuminated 3 5 1 2 Lightbar Drivers The lightbars are driven by latch circuitry and are not multiplexed U3 and U8 drive lightbars with the following signals DP lights decimal point in the 7 segment digital displays ALMINH lights AUDIO ALARM OFF lightbar N C not connected PLSSRCHLO with PLSSRCHHI lights PULSE SEARCH lightbar PLSSRCHHI with PLSSRCHLO lights PULSE SEARCH lightbar LOWSAT lights LOW SAT lightbar U2 and U9 drive the remaining lightbars with the following signals HISAT lights HIGH SAT lightbar LOWRATE lights LOW RATE lightbar HIRATE lights HIGH
12. PCB This adjustment is accessible through the hole marked 1V on the Upper Daughter PCB Set the VOLT 2 dipswitch on the rear of the N 200 to the 0 10 position Press the FULL button on the rear of the N 200 Examine the DMM for a 10 00 0 01 volts indication If necessary adjust R11 on the Middle Daughter PCB This adjustment is acces sible through the hole marked 10V on the Upper Daughter PCB Remove all test equipment and place the ON STDBY switch in the STDBY position 5 7 SYSTEM FUNCTION TEST The following tests allow for further circuit verification including using signals from the pocket tester 1 2 9 10 AC Operation Battery Operation Adult Neonatal Alarm Limits Pocket Tester Operation Alarm Limits Adjustment Temporary Alarm Silence Disabling the Audible Alarm Powerbase to Monitor Communication Monitor to Powerbase Communication Middle Daughter PCB Verification 5 7 1 AC Operation 1 Connect a patient module to the 90 Place the ON STDBY switch the ON position and verify that the N 200 operates normally N 200 emits a beep b All displays light momentarily c All displays flash in a rolling fashion N 200 goes into PULSE SEARCH mode 5 7 2 Battery Operation 1 2 Disconnect the AC power cord from the N 200 and note that the BATT IN USE indicator illuminates Reconnect the AC power cord and verify that the BATT IN
13. PULSE INDICATION PULSE RATE OR SATURATION INSTRUMENT OPERATES PULSE INDICATION NO SATURATION OR PULSE RATE DISPLAY INSTRUMENT OPERATES PULSE WAVEFORM AND SATURATION RATE VALUES NOISY INSTRUMENT OPERATES BEEPER RASPY Trend and event memories erased and reinitialized either manually or because the data were corrupted No further action required When ALL clr appears because the memory data were corrupted and erased 5 second alarm sounds simultaneously Monitor not correctly connected to power base LED on mother PCB defective Refer to Section 3 8 1 Phototransistor on power supply PCB defective Refer to Section 3 6 Note The instrument will operate if any button is pressed while Err Pb is displayed Sensor disconnected or inoperative Refer to Section 3 3 Patient module or its cable defective Refer to Section 3 3 18 V power supplies out of spec Refer to Sections 5 3 1 and 3 6 Circuit failure of the analog signal processing circuitry on the processor board Refer to Sections 5 4 and 3 4 2 A D converter circuitry failure on the proces sor board Refer to Sections 5 4 6 and 3 4 4 Defective LED drive or amplifier on proces sor board Refer to Sections 5 4 and 3 4 2 Defective red LED on the sensor Refer to Section 3 3 Defective red LED driver circuit on processor board Refer to Section 3 4 2 5 Circuit failure in the RED channel of the analog processing circu
14. RATE lightbar BATLO lights LOW BATT lightbar BATON lights BATT IN USE lightbar ECGLOST lights ECG LOST lightbar ECGON lights ECG IN USE lightbar Decoder U6 takes the select line from the processor DISPLAY and the three low address lines from the processor 0 1 and 2 and uses them to select a latch for display updating 3 5 1 3 Front Panel Controls Decoder U6 also lets the processor select octal buffer U1 which reads the state of inputs BUTTON 0 through BUTTON 4 and control knob rotation information relayed through UP DOWN U D counter U5 The control knob consists of a two channel optical chopper with the two channels mechanically 3 12 90 degrees out of phase to each other dual channel optical slot detector Schmitt trigger inverters U4 are used to clean up the signals from the knob one inverter per channel Channel A provides the clocking pulse for U D counter U5 Channel B provides the direction U D signal The phase relationship between the two channels provides an UP or DOWN count command to the counter depending on which way the knob is turned clockwise rotation results in count up commands To detect a change in the U D counter the processor reads the twos complement value of the counter s output and adds it to its accumulated turns count After it accumulates the counter value the processor generates a signal into the LOAD line of U5 to clear it for the next count value 3 5 1 4 Power Up Displ
15. SATURATION DMM 80 8 00 0 05 V 81 8 10 0 05 V 82 8 20 0 05 V Repeat steps 2 and 3 with the SaO switch set to the 50 100 position but use the values in the following table OXYGEN SATURATION DMM 80 6 00 0 05 V 81 6 20 0 05 V 82 6 40 0 05 V Disconnect all test equipment and place the ON STDBY switch to STDBY Channel 2 Channel 1 GAINCH1__ 0 2 V div COUPLING 6 GAINCH2_ NOt used COUPLING TP SWEEP SPEED 0 1 ms div SYNC eee eee Ee GAIN CH 1__2 V div cCouPLING DC 9 GAIN CH2 _ 2 V div DC 10 SWEEP SPEED 200 ms div SYNC Attachment 1 N 200 5 18 BAT ICU Point Pin 5 200 Battery Charger Board Test Point 50 180 180 200 Power Supply Board Attachment 2 N 200 5 19 TP3 J3 1 6 11 5 65 me np 1 2 1 A116 N 200 Processor Board Test Point Attachment 3 N 200 5 20 SECTION 6 This page left intentionally blank 6 1 SECTION 7 PACKING FOR SHIPMENT 7 1 REPACKING IN ORIGINAL CARTON The best package to use when packing the instrument for shipping is the original packing carton If the original packing carton is available pack the instrument as described in the following steps 1 Snap the monitor and its powerbase together and place it in its pl
16. SUPPLY PCB drawing The power supply board contains two switching power supplies in flyback converter configuration The supplies are capable of providing 2 A at 5 V 100 mA at 18 V 100 mA at 18 Pulse width modulator PWM U2 controls the 5 V supply PWM U4 controls the 18 18 V sup ply The PWMs sense the DC output voltages through their INV pin 1 inputs and control the pulse width at the gates of switching FETs 02 04 Voltage regulator VR1 provides 5 V power and a5 V reference to the two PWMs Schmitt inverters U3 provide low impedance active current drive to the somewhat capacitive gates of the FET switching transistors minimizing drain rise and fall times Also resident the power supply board is half monitor side of the powerbase monitor opti cal link formed by diode DS1 and phototransistor Q1 3 7 BATTERY CHARGER PCB The battery charger PCB is shown on the SCHEMATIC BATTERY CHARGER PCB drawing The battery charger PCB contains two major circuits ON STDBY control circuitry Battery charger circuitry 3 7 1 ON STDBY Control Circuit The ON STDBY control circuit is shown on the bottom portion of the schematic The ON STDBY switch J1 is shown in the ON position It does not switch power Rather it provides a logic control signal SWITCH that is polled by the main processor through a tri state buffer U41 on SCHEMATIC PROCESSOR PCB SHEET 4 When the processor senses a change in switch posi
17. USE indicator extinguishes 5 7 3 Adult Neonatal Alarm Limits T Locate the series of eight DIP switches on the back panel of the N 200 Make sure that DIP switch 1 is in the up position adult limits Push and hold the HI SAT button Verify that the OXYGEN SATURATION display shows an alarm limit of 100 Push and hold the HI RATE button Verify that the PULSE RATE display shows an alarm limit of 140 Use a slender nonmetallic object to move the DIP switch 1 to the down position neonatal limits Push and hold the HI SAT button Verify that the OXYGEN SATURATION display shows an alarm limit of 95 Push and hold the HI RATE button Verify that the PULSE RATE display shows an alarm limit of 200 Return DIP switch 1 to the up position adult limits and place the ON STDBY switch in the STDBY position 5 7 4 Pocket Tester Operation 1 2 Connect the PT 2500 pocket tester to the patient module Place the ON STDBY switch in the ON position Notice that after about 10 seconds delay the N 200 will begin to follow the artificial pulse and saturation values and start giving a proper SaO and Pulse Rate as per the pocket tester label Verify that the LOW SAT and LOW RATE alarms are active as follows the OXYGEN SATURATION and PULSE RATE displays and the indicators next to the LOW SAT and LOW RATE buttons are flashing and the audio alarm is sounding NOTE The alarms may be temporarily silenced while m
18. bottom cover 4 Use a small blade screwdriver to disengage the front panel latches and pry them free one at a time See Figure 4 2 5 Pull the front panel away from the bottom cover and disconnect all cables from the driver PCB For reassembly verify that the 2 conductor power cable is installed with the red lead on top the speaker cable is installed with the orange lead on top and the ribbon cable is installed with pin 1 designators aligned 4 12 Fig 4 2 Monitor front panel latch locations 4 3 4 Display PCB and Driver PCB Removal The display PCB and driver PCB are attached to the front panel the driver PCB is nearest the instrument interior Remove the two PCBs as a single unit by performing the following steps 1 If not already removed remove all connectors from the two PCBs at this time 2 Insert small screwdriver through the two holes above the encoder assembly and push off the encoder knob from the encoder shaft 3 With a deep 7 16 inch hex socket remove the encoder shaft retaining nut Remove the en coder assembly When replacing the encoder assembly be sure to replace the toothed lock washer between the retaining nut and the front panel for proper knob clearance torque on retaining nut to exceed 15 in lb Verify that the encoder cable is installed with the red white lead on top 4 Unscrew the six Phillips head screws securing the front panel to the display and driver PCBs Remove the screws in tw
19. cable from front panel LEMO connector to processor PCB noting polarity 4 Connect 20 conductor ribbon cable from processor PCB to driver PCB noting polarity 5 Replace retaining clips on all ribbon cable connectors NOTE See cable interconnect diagrams Section 9 When refitting the top cover note the following details 1 Be sure that all PCBs fit properly into the alignment slots and features provided in the case In particular note that the power supply PCB fits into a guide on the top cover and that the charger PCB is fully seated in the slot in the bottom cover Do not force the top cover down onto misaligned PCBs 2 Three tabs on the top cover mate with slots on the front panel 3 Pivot points on the side latches fit into holes in the top and bottom covers After the top cover has been fitted properly turn the instrument over and replace the four screws into the bottom cover in the following manner 1 sure that the washers in place under each screw head 2 Before tightening the screws securely check the top cover to see that its front edge mates properly with the front panel Press the top cover down into place if necessary 3 When tightening the screws be careful not to strip the threads in the plastic case by over tightening Recommended screw tightening torque is 16 to 18 in lb 4 4 POWERBASE DISASSEMBLY AND REASSEMBLY Disconnect AC power cord before attempting disassembly Unless otherwise noted
20. connects to the BATT terminal and the switch connector is oriented with brown lead on top 5 Remove the power supply PCB and battery charger PCB as one unit The PCBs can now be separated if necessary by disconnecting the 18 conductor flex circuit cable from the battery charger PCB 4 3 3 Front Panel Removal The front panel can be removed after the instrument top cover has been removed Remove the front panel from the top cover by performing the following steps 1 Turn the bottom cover upside down and remove the two Phillips head screws securing the front panel to the bottom cover 2 Disconnect the ON STDBY switch cable from the battery charger PCB For reassembly the switch connector is oriented with the brown lead on top 3 With the bottom cover right side up on the workbench locate the four latches on the front panel that secure the front panel to the bottom cover 4 Use a small blade screwdriver to disengage the front panel latches and pry them free one at a time See Figure 4 2 5 Pull the front panel away from the bottom cover and disconnect all cables from the driver PCB For reassembly verify that the 2 conductor power cable is installed with the red lead on top the speaker cable is installed with the orange lead on top and the ribbon cable is installed with pin 1 designators aligned 4 12 Fig 4 2 Monitor front panel latch locations 4 3 4 Display PCB and Driver PCB Removal The display PCB and
21. converter U43 which is compared to the held signal voltage via comparator U29 The result of this comparison is polled by the processor via buffer U41 H The SAR continues until the least significant bit has been set Each 12 bit conversion is accomplished in approximately 100 ps 3 4 4 2 D A Conversion The analog sample hold circuits formed by analog demultiplexer 018 and quad operational ampli fier U11 are used to update and store the following four analog signals VIR which controls the IR LED brightness VRED which controls the red LED brightness VOLUME which controls the speaker volume RWTHRESHOLD not used In operation the processor sets up an analog voltage on analog demultiplexer U18 pin 9 by writing to DAC U43 U18 is enabled through U18 pin 3 and the processor selects which output is written with address lines AO through A2 When U18 is enabled the voltage at U18 pin 9 is routed to one of the four outputs S1 through S4 charging storage capacitor C39 C41 C42 or C43 When U18 is disabled the capacitor voltage is held by the very low leakage follower op amp U11 until the next update 3 4 5 Timing and Control Most processor timing and control flags are generated in circuits shown on SCHEMATIC PROCESSOR PCB SHEET 2 and 3 Processor timing is affected by two types of logic flags Polled processor I O signals Processor interrupts which may occur asynchronously Many of these flags are discussed elsewhere in this
22. data are stored the trend memory and one hour of saturation pulse rate and pulse perfusion data are stored in the event memory These data can be provided to a variety of analog or digital output devices Noninvasive sensors obtain measurements by optical means alone using two light emitting diodes as light sources Specific sensors are available for use on neonates infants children and adults e Patented automatic calibration mechanisms are incorporated in the N 200 U S Patent 4 621 643 and others pending The N 200 automatically calibrates itself each time it is turned on at periodic intervals thereafter and whenever a new sensor is connected Instrument sensitivity changes automatically to accommodate a wide range of tissue thicknesses and skin pigmentations 2 1 Internally the monitor contains five printed circuit boards PCBs the battery and speaker The largest circuit board mounted on the top cover of the monitor is the processor PCB which contains the analog processing circuitry and the microprocessor with its associated circuitry The power supply PCB is located on the back of the monitor The battery charger PCB is located along the left side of the instrument chassis when viewed from the front The display and driver PCBs are located immediately behind the front panel and contain the LED displays and front panel switches The powerbase contains a power supply transformer a mother PCB and thr
23. displaced dislodged or disconnected from the ECG cable check the position of the electrodes and check the connections ECG cable has come loose from the patient module connector check the connection If the ECG signal is coming from a bedside ECG monitor the ECG input cable may have become dislodged from the ECG IN OUT connector on the rear of the N 200 or from the bedside monitor check the connection 15 Trend and event data are not available 16 17 memory back up battery has been discharged e The trend and event memory has been erased Trend or event data cannot be printed Switch settings are incorrect check the switch settings see N 200 Operator s Manual Cables are improperly connected check the cable connections The NELLCOR N 9000 recorder interface cannot be used e switch settings are incorrect check the switch settings see N 200 Operator s Manual 4 2 DETAILED TROUBLESHOOTING PROCEDURES 4 2 1 Failure Modes Instrument failures can be broadly divided into two classes An outright failure of a component in one of the instrument modules will cause consistently incorrect operation or no operation at all Use the Troubleshooting Summary below as a guide to diagnosing these failures Subsequent sections dealing with repairs to each specific module can then be used to correct the diagnosed problem The second more difficult problem deals wi
24. display see the first page of this section for details Examine the location in the PULSE RATE display for a value of 64 3 Replace the 6040 OHM 1 0 TEST RESISTOR with the 9760 OHM 1 0 TEST RESISTOR 4 location 9 again for a value of 84 These two numbers verify the range limits of the circuit which generates voltage VCAL 5 Remove all test equipment except the W3 jumper LED Intensity Control This procedure uses normal system components to test circuit operation A D 25 Sensor or equivalent disposable or flexible sensor is used to examine LED intensities The red LED is used to verify intensity modulation caused by the LED Intensity Control Circuit This test also verifies operation of the LEDLOW flag output at U20 pin 14 and the LEDHI interrupt output at U20 pin 3 1 Connect a patient module to the N 200 2 Connect the Sensor to the patient module and notice that the Red LED is visible 3 Slowly move the LED in proximity to the optical sensing element of the sensor Notice as 5 7 the LED approaches the optical sensor LED intensity will decrease Open the sensor and notice that the LED intensity will increase after a few moments Repeat step 3 and the intensity will again decrease This hunting is an indication that the microprocessor is in proper control of LED intensity 5 5 4 Input Amplifier INAMP Automatic Gain 1 2 10 11 12 Disconnect the Patient Cable connecto
25. driver PCB are attached to the front panel the driver PCB is nearest the instrument interior Remove the two PCBs as a single unit by performing the following steps 1 If not already removed remove all connectors from the two PCBs at this time 2 Insert small screwdriver through the two holes above the encoder assembly and push off the encoder knob from the encoder shaft 3 With a deep 7 16 inch hex socket remove the encoder shaft retaining nut Remove the en coder assembly When replacing the encoder assembly be sure to replace the toothed lock washer between the retaining nut and the front panel for proper knob clearance torque on retaining nut to exceed 15 in lb Verify that the encoder cable is installed with the red white lead on top 4 Unscrew the six Phillips head screws securing the front panel to the display and driver PCBs Remove the screws in two steps first loosen each screw part way then go back and remove each screw completely Note that the screws may remain in their holes held by the plastic standoffs between the PCBs 5 Remove the display and driver PCBs as one unit The PCBs are assembled with component sides exposed for easy troubleshooting access It is recommended that they not be separated unless replacement of one of the PCBs is required If necessary separate the two PCBs by decoupling connectors J6 and J4 then separate the PCBs by carefully prying the two snap in standoffs apart beginning at on
26. exposed to view Close the fuse door by exerting firm pressure against the door 4 4 2 Powerbase Disassembly The powerbase is disassembled by removing the four Phillips nhead screws from the bottom of the unit With the unit upright on the bench lift off the top cover All electronics are contained in the bottom portion of the powerbase The solder side of the upper daughter PCB is exposed 4 4 3 PCB Removal The mother PCB is mounted vertically at the front of the unit The upper middle and lower daugh ter PCBs are mounted horizontally and mated to the mother PCB The entire 4 PCB assembly can be removed as a unit by lifting the assembly out If necessary disconnect slip on connectors and the 4 conductor DIN connector from mother board To disassemble the daughter PCBs from the mother PCB hold the mother PCB and apply demating pressure between the bottom daughter PCB and the mother PCB The upper and middle daughter PCBs can now be easily disconnected from the mother PCB 4 4 4 Powerbase Reassembly During reassembly make sure that all pins on connector J3 on the bottom daughter PCB mate properly with the corresponding connector on the mother PCB Also make sure that the PCBs are 4 15 SECTION 5 TESTING AND CALIBRATION 5 1 DESCRIPTION This section details routine test and calibration procedures for the NELLCOR N 200 pulse oximeter Instructions for troubleshooting and repair of oximeter defects are detailed in Sec
27. functional 3 2 measured 3 2 SCALE signal 3 16 schematic diagrams list 9 1 sensor calibration resistor 3 2 calibration resistor circuit testing 5 7 theory of operation 3 1 3 2 3 3 shut off voltage test 5 3 5 4 signal noise ratio 3 6 SOD signal 3 16 spare parts list 8 1 speaker driver circuit 3 13 removal 4 13 successive approximation routine 3 10 SWITCH signal 3 10 3 15 sync detector 3 6 alignment 5 8 5 9 system function tests AC operation 5 13 adjusting alarm limits 5 15 5 16 adult neonatal alarm limits 5 14 battery operation 5 14 disabling the audible alarm 5 16 middle daughter PCB verification 5 17 monitor to powerbase communication 5 16 pocket tester operation 5 14 5 15 powerbase to monitor communication 5 16 temporary alarm silence 5 15 test equipment list 5 2 testing 5 1 theory of operation 3 1 timer circuits 3 5 timing and control 3 10 top cover removing 4 10 replacement 4 13 trend data not available 4 6 print failure 4 6 TREND signal 3 16 troubleshooting 4 1 initial procedures 4 1 4 2 4 3 4 5 4 6 troubleshooting summary 4 7 4 8 4 9 4 10 TxRDY signal 3 11 U UART 3 5 3 11 3 17 Upper Daughter PCB 3 16 removal 4 15 VCAL signal 3 9 verifying operation 5 1 VIR signal 3 3 3 7 3 10 voltage regulator 3 15 VOLUME signal 3 10 VPS signal 3 9 VRED signal 3 3 3 7 3 10 VREF signal 3 6 3 9 10 4 wait state generator
28. of CR2 on the Power Supply PCB 7 Raise the DC POWER SUPPLY voltage 6 volts Note If you are using the DMM to monitor the DC POWER SUPPLY make sure to reconnect it to CR2 8 Place the ON STDBY switch in the ON position Note that the N 200 powers up ina normal fashion and the BATT IN USE light is on NOTE The DMM will now be indicating around 5 4 volts 9 Very slowly decrease the DC POWER SUPPLY voltage until the N 200 LOW BATT indicator light just comes on Examine the DMM for an indication of 5 2 0 05 volts Note If the DMM indication is low you probably decreased the DC POWER SUPPLY too fast To repeat the test increase the DC POWER SUPPLY back to 6 volts and then cycle the N 200 OFF and ON to reset the LOW BATT indicator 10 Watch the DMM as you again slowly decrease the DC POWER SUPPLY voltage until the N 200 just shuts off The DMM must indicate 5 0 0 05 volts just as the N 200 shuts off NOTE The DMM reading will drop to approximately zero at shutoff because the power and system grounds are separated 11 Set the ON STDBY switch to STDBY 12 Remove all test equipment and reconnect the battery cables to the Battery Charger PCB ON STDBY Switch Test These tests verify the operation of the ON STDBY switch and the watchdog timer circuit 1 Disconnect connector J2 from the Processor PCB 10 conductor cable 2 Set the OSCILLOSCOPE as follows Channel 1 5 V div DC Coupling Sweep Rate 100 ms div Trigger Channel
29. photode tector response The detector photodiode generates a current proportional to the amount of light received SAT preamplifier U2 is a current to voltage converter in an inverting configuration that converts the DETECTOR current to a SAT voltage signal The conversion ratio is 250 mV A Voltage regulator VR1 biases the preamplifier to approximately 8 5 V output for 0 current input This bias increases the swing of the converter to an effective output swing of 8 5 V to 10 V The ad ditional voltage headroom is necessary for high ambient light conditions 3 3 Instrumentation amplifier 01 preamplifies the ECG signal Gain of the amplifier is set for mately 30 Neon lamps DS1 DS2 and DS3 are used to protect U1 from potentially damaging high energy pulses which may result from defibrillation procedures Series resistors R1 and R2 provide further isolation from high transient currents Diodes CR1 through CR4 shunt high voltage transients to the low impedance power supplies Resistors R3 and R4 pull the input signal lines to the power supply voltage levels when an ECG signal lead has become detached Common mode signals 1 and 2 from U1 are summed through R9 R10 amplified and in verted through operational amplifier U2 The output of U2 is fed back to the patient to maintain the patient at a constant potential and eliminate common mode signals from the input sensing leads The ECG signal from U1 goes
30. possible the ECU and N 200 are plugged into a common power source Operate the N 200 on battery or plug it into a different AC outlet the sensor is damp or has been reused too often Replace it with a new sensor use an OXISENSOR D 25 which has added insulation against electrosurgical interference Ambient light may be interfering with the sensor Shield the sensor from bright ambient light with opaque material The ECG LOST indicator is displayed Check the condition of the patient The ECG electrode or electrode cable is loose or unplugged Check connections If the ECG signal is supplied via the patient module the patient module may be defec tive Try another patient module If that is not possible see Sections 3 3 3 4 3 and 5 4 If the ECG signal is provided via the rear panel connector the input signal from the ECG monitor may be incorrect Use 1 V mV ECG analog output or defib sync pulse wave AC power to the powerbase may have been interrupted this applies only if the ECG signal is being supplied via the rear panel connector When EGG is connected pulse rate is displayed but saturation is not The patient s perfusion may be inadequate check the condition of the patient test the instrument on yourself or another patient try the nasal OXISENSOR R 15 The pulse rate displayed by the N 200 does not correlate with that of the ECG monitor Excessive patient motion is making it difficu
31. remain still or check whether the sensor is securely applied and replace it if necessary or 10 11 use a type of sensor that tolerates more patient motion or move the sensor to a site with less movement or use Mode 3 if appropriate Refer to the N 200 operator s manual An electrocautery unit is interfering with performance the ECU cable and N 200 patient module are too close to each other Move them as far apart as possible the sensor is too close to the ground pad or electrocautery site Move sensor to a different site if possible the ECU and N 200 are plugged into a common power source Operate the N 200 on battery or plug it into a different AC outlet the sensor is damp or has been reused too often Replace it with a new sensor use an OXISENSOR D 25 which has added insulation against electrosurgical interference Ambient light may be interfering with the sensor Shield the sensor from bright ambient light with opaque material The ECG LOST indicator is displayed Check the condition of the patient The ECG electrode or electrode cable is loose or unplugged Check connections If the ECG signal is supplied via the patient module the patient module may be defec tive Try another patient module If that is not possible see Sections 3 3 3 4 3 and 5 4 If the ECG signal is provided via the rear panel connector the input signal from the ECG monitor may be incorrect
32. section and all are summarized below 3 4 5 1 Polled Processor Flags Buffer U41 allows the 8088 processor to poll the following logic flags SWITCH indicates the state of the front panel switch logic low indicates ON position LEADOFF _ indicates that an ECG lead has become detached and that the ECG signal from the patient module was near saturation level as a result LEDLOW indicates that LED drive currents should be increased to increase SAT S N ratio DACMP the output of voltage comparator U29 used in SAR A D conversion Four jumpers W2 W3 W4 W5 which are selectively installed to place the processor in various diagnostic modes 3 4 5 2 Interrupt Processor Flags AC interrupts the processor at the frequency of the AC power line LEDHI instructs the processor to decrease the LED drive currents in the presence of ambient light to avoid SAT signal saturation indicates that the INAMP gain is set too high The processor then reduces the gain of the INAMP stage to lower the signal level to avoid saturation TxRDY signals that UART U16 is ready to transmit another character RxRDY signals that 016 has received a new character INT real time interrupt from interrupt controller U22 3 5 FRONT PANEL DISPLAY Front panel display is accomplished by two circuit boards Driver PCB which contains drive circuitry for the display LEDs Display PCB which contains the display LEDs pushbuttons 3 5 1 Driver
33. that stores the peak value of the R wave from one peak to the next SECTION 4 TROUBLESHOOTING AND ASSEMBLY GUIDE This section first discusses some potential difficulties their possible causes and suggestions for resolving them that do not require disassembly of the instrument If the difficulty persists after following these suggestions proceed to the subsections on detailed troubleshooting and disassembly Refer if necessary to Section 5 Testing and Calibration If qualified service personnel are not available contact Nellcor s Technical Service Department at 1 800 NELLCOR or 415 887 5858 NOTE Instrument must be operating on AC power for the powerbase to be functional NOTE To reset the powerbase microprocessor disconnect and reconnect AC power 4 1 INITIAL TROUBLESHOOTING PROCEDURES 1 The instrument does not turn on The AC power is not connected and the battery is discharged Connect to AC power If the problem persists check the AC fuse If this does not resolve the problem contact qualified service personnel or Nellcor s Technical Service Department 2 The instrument operates on AC power but not on the battery battery is discharged Fourteen hours are required to completely recharge the battery battery pack is defective or the battery fuse is open Contact qualified service personnel or Nellcor s Technical Service Department battery charger is defective Contact qualified service p
34. that the shroud of processor PCB connector J4 a five pin header clears the flex cable connecting the processor PCB and the battery charger PCB If cables have been disconnected during servicing refer to Figure 4 1 for the order of cable replacement Cables at the back of the unit should be connected first so that they lie below those toward the front of the unit The order is 1 Connect 5 conductor power cable from power supply PCB to processor 2 Connect 10 conductor ribbon cable from processor PCB to power supply PCB noting polarity 3 Connect patient cable from front panel LEMO connector to processor PCB noting polarity 4 Connect 20 conductor ribbon cable from processor PCB to driver PCB noting polarity 5 Replace retaining clips on all ribbon cable connectors NOTE See cable interconnect diagrams Section 9 When refitting the top cover note the following details 1 Be sure that all PCBs fit properly into the alignment slots and features provided in the case In particular note that the power supply PCB fits into a guide on the top cover and that the charger PCB is fully seated in the slot in the bottom cover Do not force the top cover down onto misaligned PCBs 2 Three tabs on the top cover mate with slots on the front panel 3 Pivot points on the side latches fit into holes in the top and bottom covers After the top cover has been fitted properly turn the instrument over and replace the four screws into
35. the demultiplexed and filtered IR detector channel signal RED the demultiplexed and filtered RED detector channel signal ECG the filtered ECG waveform VCAL the filtered voltage from the calibration resistor within the sensor VPS the power supply voltage used to determine whether the system is running on power or batteries and to check the battery voltage when the instrument is operat me on battery power ISEG a voltage level from the display driver board used to detect bad segments or bars on the display during power up test VREF approximately 10 V reference voltage used for board alignment GROUND analog ground potential used for board alignment B Set programmable amplifier U30 gain by writing to latch U42 3 9 Set desired analog offset value to be subtracted at U25 pin 2 writing two bytes low byte high nybble to 12 bit bus compatible DAC U43 12 bits 0 10 V D Now ascaled analog value is present at the output of programmable gain amplifier stage U37 pin 1 TP3 The offset voltage has been subtracted by differential amplifier U25 and amplified by programmable amplifier U30 and U37 The total range of programmable gain is 1 8 to 16 E Triggering the sample and hold line S H causes U36 to hold the scaled voltage for A D con version F The 8088 processor begins executing a successive approximation routine SAR G The SAR performs a binary search sequence by setting up a voltage on the D A
36. value in the OXYGEN SATURATION display goes below the number recorded in step 1 the HI SAT indicator begins flashing and the audio alarm sounds Still holding the HI SAT button turn the control knob clockwise until the alarms stop Press and hold the HI RATE button and turn the control counter clockwise Verify that when the value in the PULSE RATE display goes below the number recorded in step 2 the HI RATE indicator begins flashing and the audio alarm sounds Place the ON STDBY switch in the STDBY position Temporary Alarm Silence 1 Place the ON STDBY switch to ON Notice that after a few seconds delay the N 200 will begin to follow the artificial pulse and saturation values and start giving a proper and Pulse Rate as the pocket tester label Verify that the LOW SAT and LOW RATE alarms are active as follows the OXYGEN SATURATION and PULSE RATE displays and the indicators next to the LOW SAT and LOW RATE buttons are flashing and the audio alarm is sounding Press the AUDIO ALARM OFF button Verify that the red AUDIO ALARM OFF indicator and the audio alarm go off for 60 2 0 seconds Disabling the Audible Alarm 1 4 Hold the AUDIO ALARM OFF button down and turn the control knob clockwise until OFF appears in the OXYGEN SATURATION display Verify that the AUDIO ALARM OFF indicator begins to flash the LOW SAT and LOW RATE indicators remain flashing and the audio alarm is silent Reactivate
37. 00 120 V Fuse 1 4 Amp Slo blow 220 240 V Fuse 4 Amp Battery Pack Description ASSY Power Supply PCB ASSY Battery Charger PCB ASSY Speaker ASSY Processor PCB ASSY Patient Cable ASSY Encoder Front Panel ASSY Front Panel PCB Set ASSY Battery Pack ASSY On Standby Switch Cable Proc PCB Pwr Sply PCB Cable Processor PCB Display PCB Description ASSY Motherboard PCB ASSY Upper Daughter PCB ASSY Middle Daughter PCB ASSY Lower Daughter PCB ASSY AC Inlet Transformer Part No 071505 072752 073145 691011 691098 691014 Part No 072268 072270 072487 072700 072756 072757 072758 073136 073217 053138 053142 Part No 072120 072140 072150 072160 073820 Item numbers are keyed to the chassis level assembly views in Section 8 4 8 3 MECHANICAL PARTS 8 3 1 Monitor 4 16 4 17 4 19 4 20 4 21 4 22 4 23 4 24 8 3 2 Powerbase Item Description Wire Bail Bottom Cover Gasket Bottom Cover Gasket Top Cover Keypad Front Panel Top Cover Front Panel Window Red Front Panel Screw Top Cover Rubber Bumper Bottom Washer Top Cover Screw Proc PCB hold down Latch Spring Latch Compression Washer Proc PCB hold down Patient Module Velcro Strap Knob Front Panel Retaining Ring for Knob Clip 20 Pin Connector Clip 14 Pin Connector Clip 10 Pin Connector Washer LEMO Connector Nut LEMO Connector Screw Display Panel Assy Des
38. 1 3 Connect the OSCILLOSCOPE ground lead to R4 on the Battery Charger pointing toward the rear of the N 200 4 Connect the OSCILLOSCOPE Channel 1 to R6 on the Battery Charger PCB end pointing the rear of the N 200 5 OSCILLOSCOPE must indicate a logic low or approximately 0 volts 5 4 5 4 6 Place the ON STDBY switch in the ON position The OSCILLOSCOPE trace must show a momentary logic high approximately 5 volts for 200 50 0 ms and then return to a logic low 7 Place the ON STDBY switch the STDBY position 8 Remove all test equipment and reconnect connector J2 to the Processor PCB 5 3 5 Battery Operation Further verify proper battery operation by charging the batteries for 14 hours and operating the N 200 on battery power with a pocket tester attached and the alarms disabled The N 200 must operate for a minimum of 2 0 hours Failure of any of the above tests indicates a malfunction and the instrument is subject to repair REGULATED POWER SUPPLY PCB TESTS The following tests verify correct operation of the following components 1 The 5 00 Power Supply 2 The 18 00 Volt Power Supply These voltages are generated by two independent power supply sections on the PCB both consisting of pulse width modulation control chips and associated circuitry All three outputs should be carefully checked for voltage and noise Since the power supply is a switching type DC to DC converter it is quite possi
39. 64 kbyte ROM are repeated up to the 512 kbyte limit because memory is not uniquely decoded RAM begins at address 0 and extends for 32 kbytes I O functions reside directly above RAM starting at address hex 8000 The I O select lines coming from U17 and U23 are 16 addresses apart ranging from hex 8000 to hex 80 3 4 1 3 Wait State Generator Two D type flip flops in U1 form a wait state generator A wait state of one clock cycle is generated whenever I O is addressed that is whenever a peripheral device is accessed Accessing RAM addresses between 0 and 32k generates no wait state 3 4 1 4 Clock Generator U2 produces a processor clock with the correct duty cycle as well as a peripheral clock which drives UART U16 and the two timer chips U34 and U38 Because the 8088 processor U8 requires a 33 duty cycle clock the crystal oscillator runs at 22 1184 MHz three times the desired fre quency U2 divides the 22 1184 MHz signal by three and provides the correct duty cycle to U8 A reset circuit composed of R1 CR1 and C19 ensure that U2 pin 11 is held low immediately following power up This maintains the logic at a known state while the power supplies and crystal oscillator stabilize 3 4 1 5 Timer Circuits and UART Additional peripheral devices include two 82C53 triple counter timer chips U34 U38 and UART device U16 The 82C53 sections control 1 Display update interrupts to the 8088 at a 2 5 ms rate also provides for re
40. 997 0 017 or 9 980 Example 2 a TP 3 voltage in step 6 0 017 volts b TP 1 voltage in step 8 9 997 volts c The algebraic sum will be 9 997 0 017 or 10 014 Connect the DMM lead to TP 3 on the Processor PCB Adjust R116 to read the value calculated in step 9 Connect the DMM lead to TP 5 on the Processor PCB Set the following memory locations as specified 197 255 198 15 Adjust R130 to read 9 997 to 9 998 volts DC GLPT all trimpots to prevent vibrational shifts REMOVE JUMPER W3 WARNING Leaving JUMPER W3 the circuit could affect normal instrument operation Remove all test equipment and place the ON STDBY switch in the STDBY position Reconnect the connector to J3 on the Processor PCB 5 5 10 Clock Calendar Lithium Battery Test 5 6 The clock calendar assembly U15 includes a lithium powered clock chip mounted in the center of the special socket under the RAM chip Battery failure will cause a momentary Err 6 display upon instru ment power up and loss of trend data The combination of these two events is not exclusive to lithium battery failure but suggests this may be a possibility The following steps describe testing this battery 1 Place the ON STDBY switch to STDBY to prevent the power supply from masking the lithium voltage value 2 Connect the DMM lead to U15 pin 14 lithium battery voltage 3 Connect the DMM lead to U15 pin 28 lithium battery voltage 4 The DMM must indica
41. B TESTS 5 5 PROCESSOR PCB TESTS 5 6 POWERBASE TESTS 57 SYSTEM FUNCTION TESTS WARNING AAMI approved electrical safety testing should be performed after any repairs are completed The procedures assume that the N 200 Monitor and Powerbase cover have been removed and the technician has access to the inside of the instrument During the tests various diagnostic routines are used The routines are invoked by accessing memory locations and inserting specified values after an enabling jumper has been installed A memory loca tion is selected by holding down the bottom and top front panel push buttons AUDIO ALARM OFF and HIGH SAT while turning the front panel selector knob until the specified memory location number appears in the OXYGEN SATURATION display The selected location is then altered by holding in the bottom and second from the top buttons AUDIO ALARM OFF and LOW SAT while adjusting the selector knob until the specified number appears in the lower PULSE RATE display Example A certain routine might be called out as 199 6 The memory location is 199 and the specified value to be entered is 6 199 would be selected and appear in the OXYGEN SATURATION display 6 would then be selected and appear in the PULSE RATE display This document is accompanied by test point maps for each circuit board to assist in locating measurement points and attachments to assist in evaluating oscilloscope traces 5 1 5 2 5 3 REQUIRED TEST EQUIP
42. INAMP automatic gain 3 6 3 7 testing 5 8 INAMPHI signal 3 7 3 11 INT signal 3 11 IR Channel Gain verification 5 9 IR signal 3 7 3 9 IRGATE signal 3 6 ISEG signal 3 9 J jumpers 3 11 3 16 L LEADOFF signal 3 8 3 9 3 11 LED drive circuit 3 7 LED drive current 3 3 3 6 LED intensity control 5 7 LEDHI signal 3 7 3 11 LEDLOW signal 3 7 3 11 light absorption 3 1 lightbar drivers 3 12 logic flags 3 7 low battery instrument shut off voltages 5 3 5 4 Lower Daughter PCB 3 16 3 17 removal 4 15 LOWRATE signal 3 12 LOWSAT signal 3 12 measured saturation 3 2 memory location setting 5 8 memory map 3 5 memory value setting 5 8 Middle Daughter PCB 3 17 removal 4 15 verification 5 17 microprocessor 3 4 memory map 3 5 operation 5 3 5 4 monitor description 2 2 disassembly and reassembly 4 10 4 11 4 12 4 13 monitor to powerbase communication 5 16 Mother PCB 3 16 removal 4 15 N N 9000 recorder interface 4 6 N C signal 3 12 NCLK 3 5 3 8 noise beeper 4 9 noise level tests 5 5 notch filter 3 5 3 8 3 9 offset amplifier 3 8 ON STDBY control circuit 3 14 switch test 5 4 oxygen saturation blood gas correlation 4 5 CO Oximeter correlation 4 5 no display 4 2 4 4 4 9 P packing instrument 7 1 patient cable 2 1 patient module difficulty in connecting 4 3 substitution 4 3 theory of operation 3 3 pattern generator 3 6 PCB locatio
43. MENT The following test equipment is required to perform the procedures described in this section 1 9 10 OSCILLOSCOPE 50 mHz dual channel 10 1 probes with 20 pf maximum input capacitance Tektronix 465 or equivalent DIGITAL MULTIMETER DMM 4 1 2 digits 0 1 accuracy DC volts AC volts and ohmeter functions FUNCTION GENERATOR 1 Hz to 1 kHz with DC level offset adjustment DC POWER SUPPLY variable voltage 0 10 volts 0 2 amps TEST RESISTOR 10 ohms 10 2 Watts TEST RESISTOR 6 040 ohms 1 TEST RESISTOR 9 760 ohms 1 NELLCOR D 25 sensor or any NELLCOR flexible sensor NELLCOR pocket tester model PT 2500 TIMER 0 60 seconds BATTERY CHARGER PCB TESTS These steps verify correct operation of the battery charging circuitry the low battery power ON OFF control circuit and parts of the Power Supply PCB that must be functional to conduct these tests The tests listed below will be performed and adjustment details if any explained 1 2 5 3 1 Raw DC Voltage both AC and battery operation Battery charging Voltage Low Battery Instrument Shutoff Voltages ON STDBY Switch Test Battery Operation Raw DC Voltage These steps test the power transformer capacitor C2 rectifier U1 on the Power Supply PCB and the battery If any of these components are defective the Battery Charger PCB will not function properly 1 Verify that the power cord is disconnected from the N 200 2 Set the
44. Manual 4 3 MONITOR DISASSEMBLY AND REASSEMBLY Unless otherwise noted the method used for reassembly of the instrument or one of its subas semblies is the reverse of that used for disassembly 4 3 1 Top Cover Removal Remove AC power cord from the instrument Disconnect the powerbase Place the instrument top down on a flat work surface Remove the four Phillips head screws from the bottom of the instru ment taking care not to lose washers Turn the instrument over with the front panel facing you Lift off the top cover and place it on your left as shown in Figure 4 1 leaving all internal connecting cables in place Hold the spring loaded latches located at the back of the monitor securely in the bottom cover while the top cover is being removed If the latches come out reassemble them in 4 10 the bottom cover In its opened condition with all cables connected the instrument may be operated normally for calibration and troubleshooting Figure 4 1 shows the placement of PCBs within the top and bottom covers The processor PCB is on the top cover held with two screws There are two washers under each screw The power supply PCB is on the back edge of the instrument The battery charger PCB is on the left side Fig 4 1 Monitor PCB locations 4 3 2 Power Supply PCB and Battery Charger PCB Removal The power supply PCB and battery charger PCB can be removed after the instrument top cover has been removed Remove the t
45. ON STDBY switch to STDBY 3 Set the OSCILLOSCOPE as follows Channel 1 2V div DC coupled Sweep Rate 10 ms div Trigger Channel 1 5 2 5 3 2 5 3 3 10 11 Connect the OSCILLOSCOPE ground to the AGND test point on the Processor Connect OSCILLOSCOPE channel 1 input to the cathode bar end of CR2 on the Power Supply PCB The OSCILLOSCOPE must read 0 volts Place the ON STDBY switch in the ON position The OSCILLOSCOPE must read between 5 2 and 6 4 volts DC with ripple and noise less than 1 50 volts p p NOTE The actual DC voltage will depend on the battery voltage Connect the power cord to the N 200 and plug it into an AC outlet The OSCILLOSCOPE must read between 10 and 15 volts DC with ripple and noise less than 1 50 volts p p NOTE The actual DC voltage will depend on the AC line value Disconnect the OSCILLOSCOPE from the N 200 Battery Charging Voltage Note There are two versions of this assembly 2270 and 6240 The test results are given for the 6240 and if differences exist in parenthesis for the 2270 These steps will test the battery charging circuit consisting of CR6 VR1 Q2 CR9 Additionally proper adjustment of the battery charging voltage will be discussed 1 2 9 Disconnect the AC power cord from the 200 Disconnect the RED and BLACK battery leads from the Battery Charger PCB CAUTION There is approximately 6 VDC on these connectors C
46. PCB The entire 4 PCB assembly can be removed as a unit by lifting the assembly out If necessary disconnect slip on connectors and the 4 conductor DIN connector from mother board To disassemble the daughter PCBs from the mother PCB hold the mother PCB and apply demating pressure between the bottom daughter PCB and the mother PCB The upper and middle daughter PCBs can now be easily disconnected from the mother PCB 4 4 4 Powerbase Reassembly During reassembly make sure that all pins on connector J3 on the bottom daughter PCB mate properly with the corresponding connector on the mother PCB Also make sure that the PCBs are 4 15 SECTION 4 TROUBLESHOOTING AND ASSEMBLY GUIDE This section first discusses some potential difficulties their possible causes and suggestions for resolving them that do not require disassembly of the instrument If the difficulty persists after following these suggestions proceed to the subsections on detailed troubleshooting and disassembly Refer if necessary to Section 5 Testing and Calibration If qualified service personnel are not available contact Nellcor s Technical Service Department at 1 800 NELLCOR or 415 887 5858 NOTE Instrument must be operating on AC power for the powerbase to be functional NOTE To reset the powerbase microprocessor disconnect and reconnect AC power 4 1 INITIAL TROUBLESHOOTING PROCEDURES 1 The instrument does not turn on The AC power is not connected and the battery i
47. SERVICE MANUAL NELLCOR N 200 PULSE OXIMETER NOTICE This manual is provided for the purpose of servicing the NELLCOR N 200 pulse oximeter It is provided without charge by Nellcor Incorporated This manual contains unpublished proprietary information and is not to be copied transmitted or used for any other purpose Additional copies are available upon request by writing the Company at the address below Caution Federal law U S restricts this device to sale by or on the order of a physician Nellcor Incorporated Pleasanton CA 94588 U S A 1 800 1994 Nellcor Incorporated 057276B S N WARNING NELLCOR N 200 pulse oximeter contains no user servicable parts For pro tection against electrical hazard refer all servicing to qualified personnel WARNING For continued protection against fire hazard replace fuses only with the same type and rating WARNING The NELLCOR N 200 pulse oximeter is a patient connected medical device An isolated patient connector is provided to protect the patient from potentially dangerous electrical potentials or ground paths To protect the integrity of this connection the proce dures and part specifications contained in this manual must be adhered to TABLE OF CONTENTS SECTION 1 INTRODUCTION Page 1 1 SECTION 2 DESCRIPTION OF INSTRUMENT 2 1 SECTION 3 THEORY OF OPERATION 3 1 3 2 3 4 3 5 3 6 3 7 GENERAL THEORY 3 1
48. Y state if an abnormal condition hangs the processor 3 7 1 2 ON to STDBY The ON to STDBY transition can occur either by placing switch J1 in position 1 STDBY or in response to a decline in battery voltage below approximately 5 6 V Placing J1 in the STDBY position causes the voltage on the polled SWITCH signal to rise If this occurs or if battery voltage falls below 5 6 V the processor blanks the front panel displays and executes an infinite loop routine that does not involve pulsing PSEN As a result watchdog timer capacitor C2 is not discharged U1 pin 9 voltage rises U1 pin 8 voltage falls and flip flop U2 is cleared The resulting logic low at U2 5 shuts off FET Q1 placing the instrument the STDBY state 3 7 1 3 STDBY State With the front panel switch in the STDBY state VPS charges capacitor C5 and the SWITCH signal is maintained at logic high SWITCH voltage is clamped to logic levels by protection zener diode CR8 Zeners 1 and perform similar functions elsewhere in the circuit In STDBY capacitor C2 is charged to 5 V through resistor 5 3 7 1 4 STDBY to ON State When the switch is moved to the ON position C5 discharges through R7 and provides a momen tary positive voltage pulse to Schmitt NAND gate U1 pins 4 and 5 In response U1 pin 6 falls to logic low discharging capacitor C2 through diode 5 and setting D type flip flop U2 When the flip flop is set U2 pin 5 goes
49. Y switch to STDBY and back to ON ON STDBY switch is damaged Instrument is inoperative on battery Refer to Section 5 3 Jumpers W1 and W4 not installed properly Note The instrument will operate if any button is pressed while Err 5 is displayed Battery backed memory contents lost trend and event memories erased and reinitialized Memories will operate normally while N 200 is turned on but when N 200 is turned to STDBY memory contents will be erased This error message may indicate that RAM socket assembly U15 needs to be replaced Refer to Section 5 5 10 Err 6 may also briefly appear when N 200 is first turned on after monitor EPROM has been replaced with a different version No action required 11 12 13 14 15 16 INSTRUMENT OPERATES SHOWS ALL clr INSTRUMENT OPERATES SHOWS Err Pb INSTRUMENT OPERATES NO PULSE INDICATION PULSE RATE OR SATURATION INSTRUMENT OPERATES PULSE INDICATION NO SATURATION OR PULSE RATE DISPLAY INSTRUMENT OPERATES PULSE WAVEFORM AND SATURATION RATE VALUES NOISY INSTRUMENT OPERATES BEEPER RASPY Trend and event memories erased and reinitialized either manually or because the data were corrupted No further action required When ALL clr appears because the memory data were corrupted and erased 5 second alarm sounds simultaneously Monitor not correctly connected to power base LED on mother PCB def
50. aking these tests by depressing the AUDIO ALARM OFF button Set the OSCILLOSCOPE as follows Channel 1 0 200 V div AC coupling Sweep Rate 0 100 ms div 5 14 10 12 13 Trigger Channel 1 auto Connect the OSCILLOSCOPE ground to AGND on the Processor PCB Connect the OSCILLOSCOPE channel 1 to TP 6 on the Processor PCB Examine the OSCILLOSCOPE trace to verify that the signal complies with that shown in Attachment 1 Waveform A The signal is essentially centered around zero volts and has a period of 333 10 microseconds and represents typical on off sequences of one of the sensor LEDs The pulse amplitude not including transient spikes must be 260 100 millivolts Set the OSCILLOSCOPE as follows Channel 1 2 V div DC coupling Channel 2 2 V div DC coupling Sweep Rate 200 ms div Trigger Channel 1 auto Connect the OSCILLOSCOPE channel 1 to TP 9 on the Processor PCB Connect the OSCILLOSCOPE channel 2 to TP 10 on the Processor PCB Examine the OSCILLOSCOPE traces to verify that the signals comply with those shown on Attachment 1 Waveform B The DC offset for the channel 1 signal can be between 4 and 5 volts The DC offset for the channel 2 signal can be between approximately 8 and 10 volts The signal amplitude may vary from 100 to 200 millivolts p p but the important point is that Channel 1 TP 9 IR is 1 2 the amplitude of Channel 2 TP 10 RED Simultaneously press the HI SAT a
51. al time references within the system program 2 Baud rate for the 8251 UART U16 which drives an optical data link for communication between the monitor and powerbase The baud rate is set at 19 2 kbaud 3 Audio frequency generation for the alarm beeper TONE 4 Clock frequency for the ECG switched capacitor notch filter NCLK 5 Pattern generator clock frequency the pattern generator is composed of U39 U35 and U28 which controls synchronous circuit operations 3 5 3 4 1 6 Pattern Generator The pattern generator U39 U35 and U28 provides software selectable timing patterns used to control sync detector gating LED control and power supply synchronization triggers In operation a preprogrammed bit pattern in EPROM U35 is continuously cycled through by coun ter U39 clocked by the divided down processor clock output One of eight patterns can be se lected through address lines A8 A10 on U35 through octal latch U40 Additional latch U28 serves to de glitch the EPROM outputs by holding the last output byte while the counter steps to the next address Various patterns within the EPROM are used to select LED sync detector sampling speeds along with real time calibration patterns and diagnostic timing 3 4 2 Analog Front End and LED Current Drive The analog circuitry and LED drive circuitry is shown on SCHEMATIC PROCESSOR PCB SHEET 2 3 4 2 1 Main Analog Signal Flow The SAT signal from the patient module passe
52. astic bag The plastic bag is necessary to prevent abrading the instrument s front panel during shipment Place the instrument in the bottom piece of supporting foam making sure that the ON STNDBY switch on the bottom of the instrument fits into the recess made for it in the foam Place the upper foam pad on top of the instrument Place the instrument accessories patient module power cord etc in the original accessories box and place the accessories box on top of the upper foam pad Securely seal the carton with packing tape 7 2 PACKING IN DIFFERENT CARTON If the instrument s original packing carton is not available pack the instrument as described in the following steps 1 2 Snap the monitor and its powerbase together and place it in a plastic bag Find a sturdy cardboard carton large enough to provide at least 2 inches of clearance on all sides of the instrument Fill the bottom of the carton with 2 inches of loose styrofoam packing material Place the instrument on the packing material and place the accessories on top of the instrument Fill the box completely with loose styrofoam packing material and securely seal the carton with packing tape SECTION 8 SPARE PARTS 8 1 EXTERNAL PARTS 8 2 ELECTRICAL ASSEMBLIES 8 2 1 Monitor 8 2 2 Powerbase Description ASSY Power Cord Patient Module 13 Patient Module 20 Fuse 1 2 Amp Slo blow 1
53. ation and improper repair proce dures can adversely affect the instrument s calibration For the protection of service personnel and patients the procedures described in this manual are only to be performed by qualified service personnel Repair and testing of the instrument exposes service personnel to potentially hazardous volt ages and improper repair or adjustment may affect the accuracy or patient protection associated with the instrument Where appropriate warnings or cautions have been included in the text of this manual The term WARNING is used to bring attention to a procedure or precaution that is important to ensure the safety of the service personnel or possibly the patient The word CAUTION brings attention to a procedure that should be carefully followed in order to prevent damage to the instrument or an error in calibration or performance It is important that these warn ings and cautions be read carefully and followed 1 1 SECTION 2 DESCRIPTION OF THE INSTRUMENT The N 200 pulse oximeter is intended for continuously monitoring arterial oxygen saturation and pulse rate The measurement is made noninvasively by applying a reusable clip on or disposable adhesive attached sensor to a finger or other site on the patient to be monitored The instrument is a portable unit weighing about 8 pounds total with a self contained battery intended for operation for periods of up to 2 hours during power fail
54. ay Element Test Differential amplifier U7 senses the power return line of driver ICs U8 09 and 011 by monitoring the voltage across resistor R9 The sensed voltage is proportional to the current flowing through the driver ICs The voltage is amplified with a gain of 10 and is provided to the A D converter as signal ISEG PROCESSOR PCB SHEET 4 024 The processor digitizes ISEG and uses it during the power up display test to determine whether any display element has a shorted or open LED segment 3 5 1 5 Speaker Driver Circuit The sample hold VOLUME signal from the processor SCHEMATIC PROCESSOR PCB SHEET 4 U11 controls the amount of current going into the speaker s SPEAKER lead The TONE signal SCHEMATIC PROCESSOR PCB SHEET 1 038 and 09 switches FET Q2 to alternately connect or disconnect the SPEAKER lead from ground The frequency of the TONE signal determines the pitch of the sound produced The harsh sounding square wave of TONE is softened by filter capacitor C6 Diode CR1 suppresses transients from the inductive speaker load Transistor Q1 supplies a current boost for the U7 operational amplifier 3 5 2 Display PCB The display circuit board is located immediately behind the front panel and contains the numeric LEDs the LED indicator lamps the control buttons and the control knob as well as associated current limiting and pull up resistors 3 6 POWER SUPPLY PCB The power supply circuitry is shown on the SCHEMATIC POWER
55. base to Monitor Communication 5 16 5 7 9 Monitor to Powerbase Communication 5 16 5 7 10 Middle Daughter PCB Verification 5 17 Attachment 1 5 18 Attachment 2 5 19 Attachment 3 5 20 SECTION 6 ADDITIONAL SERVICE INFORMATION 6 1 SECTION 7 PACKING FOR SHIPMENT 7 1 7 1 REPACKING IN ORIGINAL CARTON 7 1 7 2 PACKING IN DIFFERENT CARTON 7 1 SECTION 8 SPARE PARTS 8 1 8 1 EXTERNAL PARTS 8 1 8 2 ELECTRICAL ASSEMBLIES 8 1 8 2 1 Monitor 8 1 8 2 2 Powerbase 8 1 8 3 MECHANICAL PARTS 8 2 8 3 1 Monitor 8 2 8 3 2 Powerbase 8 2 8 4 CHASSIS LEVEL ASSEMBLY VIEWS 8 3 SECTION 9 SCHEMATIC DIAGRAMS 9 1 SECTION 10 INDEX 10 1 NELLCOR OXIBAND DURASENSOR OXISENSOR and C LOCK are trademarks of Nellcor Incorporated SECTION 1 INTRODUCTION This manual covers test and repair of the NELLCOR N 200 pulse oximeter The N 200 is identi fied by its two piece construction The front part of the N 200 is the monitor the back part of the N 200 is the powerbase The monitor receives processes and stores patient pulse data the powerbase provides AC power to the monitor and drives peripheral display and recording devices Communication between monitor and powerbase is provided by a bi directional optical link This manual is provided to qualified service personnel for the purpose of maintaining and repairing the NELLCOR N 200 pulse oximeter Dangerous voltages are exposed when the cover is removed certain components are critical to maintain patient isol
56. ble that a component failure may not cause supply failure but may introduce unacceptable noise levels on the output This procedure requires that noise measurements be made Noise measurements may include a fine grass at the power supply switching frequency of 45 kHz The grass component is somewhat dependent on measurement technique and the oscilloscope probe being used The 45 kHz grass is not part of these noise measurements The noise of concern in these measurements is between 100 and 1000 Hz Some display LED load switching variations may also be observed This component is acceptable if it is within the 100 mV limits If a noise problem is suspected and not identified in the following tests repeat the noise tests at an elevated temperature of 40 deg C with the cover in place or 50 C without the cover 1 Connect the N 200 to an AC power source and set the ON STDBY switch to ON 2 Connect the DMM lead to AGND on the Processor 3 Connect the DMM lead to the cathode bar of CR1 on the Power Supply PCB The DMM must indicate 5 00 0 15 volts DC 4 Place the DMM lead to FB2 on the Power Supply PCB The DMM must indicate 18 00 1 8 0 5 or 17 50 to 19 80 volts 5 Place the DMM lead to pin E5 on the Power Supply PCB The DMM must read 18 00 0 50 1 80 or 17 50 to 19 80 volts 6 Remove the DMM from the circuit 5 5 5 5 10 11 12 Set the OSCILLOSCOPE as follows
57. cription Top Cover Bottom Cover Backplate Pushbutton Cap Screw Powerbase Covers Screw Transformer Attachment Part No 052248 052258 053567 052577 053724 052719 872063 759110 860202 871031 052262 891064 891074 052283 054235 891050 491100 491099 491098 491005 491006 871056 053374 Part No 053897 052141 052174 639101 872163 873100 Item numbers are keyed to the chassis level assembly views in Section 8 4 8 4 CHASSIS LEVEL ASSEMBLY VIEWS Monitor Chassis Page 8 4 Monitor Top Cover 8 5 Monitor Front Panel Powerbase 8 7 N 200 Monitor Chassis 8 4 N 200 Monitor Top Cover 8 5 SECTION 9 SCHEMATIC DIAGRAMS Page Processor PCB Schematic Sheets 1 through 4 9 2 Processor PCB Assembly 9 6 Display PCB Schematic 9 7 Display PCB Assembly 9 8 Driver PCB Schematic 9 9 Driver PCB Assembly 9 10 Power Supply PCB Schematic 9 11 Power Supply PCB Assembly 9 12 Battery Charger PCB Schematic 9 13 Battery Charger PCB Assembly 9 14 Patient Module PCB Schematic 9 15 Patient Module PCB Assembly 9 16 Mother PCB Powerbase Schematic 9 17 Mother PCB Powerbase Assembly 9 18 Upper Daughter PCB Powerbase Schematic 9 19 Upper Daughter PCB Powerbase Assembly 9 20 Middle Daughter PCB Powerbase Schematic 9 21 Middle Daughter PCB Powerbase Assembly 9 22 Lower Daughter PCB Powerbase Schematic 9 23 Lower Daughte
58. directly to the processor board The sensor contains a calibration resistor that codes the wavelength of the red LED mounted in the sensor Because the wavelength of the red LED varies from one sensor to another an error would result in the computation for oxygen saturation if not corrected for by the calibration resis tor This calibration resistor is connected directly through the instrument cable assembly to the processor board Since the patient module assembly is used close to the patient environment it is potted in epoxy to prevent any damage from moisture and is not repairable In the event of failure or damage to the sensor contacts or to the cable or connector itself the entire assembly must be replaced 3 4 PROCESSOR PCB The processor PCB contains most of the active circuitry in the N 200 both analog and digital Refer to SCHEMATIC PROCESSOR PCB SHEETS 1 through 4 in the following discussion 3 4 1 Digital Section The digital section of the N 200 processor PCB is shown on SCHEMATIC PROCESSOR PCB SHEET 1 3 4 1 1 Microprocessor Subsection The processing power of the N 200 pulse oximeter is contained within a standard 8088 minimum mode microprocessor RAM ROM configuration Program memory is contained in one 64K x 8 EPROM U21 while the 32K x 8 system RAM U15 provides a data buffer stack scratchpad and trend and event data memory functions The RAM is mated to a clock calendar socket which pro vides time and date i
59. dule If no spare patient module is available or replacement does not resolve the problem refer to Sections 3 3 Patient Module 3 4 2 Analog Front End and LED Current Drive and 5 4 Processor PCB Tests Perfusion amplitude indicator tracks a pulse but there is no oxygen saturation or pulse rate display The sensor is damaged red LED Replace with another sensor The patient s perfusion is too low to allow the instrument to measure saturation and pulse rate fewer than three or four bars on the perfusion display check the condition of the patient use C LOCK ECG synchronization test the instrument on yourself or another patient try the nasal OXISENSOR R 15 Excessive patient motion is making it difficult for the instrument to find the actual pulse pattern use C LOCK ECG synchronization set the N 200 for Mode 3 refer to Operator s Manual Patient module cannot be connected to the instrument Incorrect type of patient module is being used Use a NELLCOR N 200 series patient module The connector pins are bent Straighten them carefully or replace the patient module the plug is internally sealed and should not be disassembled Saturation and or pulse rate display are changing rapidly and pulse amplitude indicator is erratic Excessive patient motion is making it difficult for the instrument to find a pulse pattern use C LOCK ECG synchronization or if possible ask the patient to
60. e end of the two board assembly 4 3 5 Battery Pack Removal Fuse Replacement The battery pack can be removed with the instrument front panel in place 1 The in line fuse holder and negative lead from the battery pack are secured to aclip by a tie wrap Cut this tie wrap to free the battery cables For fuse replacement untwist halves of in line fuse holder and replace fuse with one of same type and rating 2 Remove the two screws from the battery retaining clip and lift out the battery pack 4 3 6 Speaker Removal To remove the speaker detach the speaker connector and remove the four speaker mounting screws 4 3 7 Top Cover Replacement Refold the connector cables to their original contours so that the top cover fits securely without be ing forced Take care that cables do not interfere with bosses or other obstructions on the cover In 4 13 particular make sure that the shroud of processor PCB connector J4 a five pin header clears the flex cable connecting the processor PCB and the battery charger PCB If cables have been disconnected during servicing refer to Figure 4 1 for the order of cable replacement Cables at the back of the unit should be connected first so that they lie below those toward the front of the unit The order is 1 Connect 5 conductor power cable from power supply PCB to processor 2 Connect 10 conductor ribbon cable from processor PCB to power supply PCB noting polarity 3 Connect patient
61. e positive sine wave cycle which exceeds an approximately 10 V peak i e 20 V p p This positive pulse is the microprocessor flag INAMPHI which initiates INAMP gain reduction 5 5 5 Sync Detector Alignment 5 8 Prior to performing this test make sure the 200 has been operating more than 5 minutes Select memory location 193 and adjust its value until OSCILLOSCOPE Channel 1 is 10 volts p p Connect Channel 2 to TP 10 and increase Channel 2 gain to 20 mV div or higher resolution if available AC Coupled The signal will be fuzzy but the 10 Hz component will be evident NOTE A Low Pass Filter can be used to remove the 50 kHz noise as long as the pass band includes up to 15 kHz Adjust R123 to null the 10 Hz component of the signal viewed on Channel 2 The final null must be less than 10 mV p p Connect the OSCILLOSCOPE Channel 2 to TP 9 and verify that TP 9 signal is also less than 10 mV p p 5 5 6 IR Channel Gain 1 Set the FUNCTION GENERATOR follows Function Sinewave Frequency 10 Hz Output 0 5 V zero offset Connect the FUNCTION GENERATOR ground to AGND Connect the FUNCTION GENERATOR output to U7 pin 12 IR Channel input Set the OSCILLOSCOPE as follows Channel 1 2 V div DC Coupled Sweep Rate 200 ms div Trigger Channel 1 auto Connect the OSCILLOSCOPE Channel 1 to TP 9 IR Channel output on the Processor PCB Verify the signal level measures 5 to 7 volts p p 5 5 7 RED Chann
62. e powerbase is plugged in and the monitor is correctly installed on the powerbase If the message does not disappear contact qualified service personnel or Nellcor s Technical Service Department Note The instrument will operate if any button is pressed while Err Pb is displayed 5 Perfusion indicator is not tracking pulse PULSE SEARCH indicator is on and saturation and pulse rate are not displayed The sensor is improperly applied to the patient or it is not plugged in Check and correct if necessary The patient s perfusion is too poor for the instrument to detect an acceptable pulse check the condition of the patient use C LOCK ECG synchronization test the instrument on yourself or another patient try the nasal OXISENSOR R 15 The sensor is damaged Replace with another sensor The patient module is damaged Try another patient module If no spare patient module is available or replacement does not resolve the problem refer to Sections 3 3 Patient Module 3 4 2 Analog Front End and LED Current Drive and 5 4 Processor PCB Tests Perfusion amplitude indicator tracks a pulse but there is no oxygen saturation or pulse rate display The sensor is damaged red LED Replace with another sensor The patient s perfusion is too low to allow the instrument to measure saturation and pulse rate fewer than three or four bars on the perfusion display check the condition of the patient
63. eaches comparator U20 The orientation of diode CR8 causes the circuit to be sensitive only to negative going signals 3 4 2 5 LED Drive Circuitry The analog switches in U19 allow the gating of separate drive voltages VRED and VIR for the red and IR LEDs so that the two LEDs can be run at different intensities VRED and VIR are deter mined by the SAT signal level from the photodetector patient module and set by the sample hold subsection SCHEMATIC PROCESSOR PCB SHEET 4 U18 U11 on the processor board Control signals RED and IR come from the pattern generator SCHEMATIC PROCESSOR SHEET 1 U28 Drive circuitry converts the VRED and VIR voltages to drive currents The voltage level at TP8 is translated to current for LED drive via a bridge driver circuit consist ing of error amplifier U32 and the six signal transistors Q2 through Q7 The bridge output J3 pins 7 and 9 goes to the back to back IR red LEDs of the sensor assembly In operation the signals RED and IR select IR or red LED drive determining the half of the bridge circuit that is active and forward biasing either the red or IR LED Q3 and Q6 act as current boosters for U32 while Q2 Q4 Q5 and Q7 steer the current flow The current through the LEDs is sensed by resistor R12 and fed back to pin 13 of error amp U32 thus maintaining a constant current proportional to volt age at TP8 and independent of the 5 V supply that powers the bridge Maximum LED current is approx
64. eaker Driver Circuit 3 13 3 13 3 5 2 Display PCB POWER SUPPLY PCB 3 13 BATTERY CHARGER PCB 3 14 3 7 1 ON STDBY Control Circuit 3 14 3 7 1 1 ON State 3 14 3 7 1 2 ON to STDBY 3 14 3 7 1 3 STDBY State 3 15 3 7 1 4 STDBY to ON State 3 15 3 7 1 5 Voltage Regulator 3 15 3 7 1 6 Power On Time Delay 3 15 3 7 2 Battery Charger Circuit 3 15 3 8 POWERBASE 3 8 1 Mother PCB 3 8 2 Upper and Lower Daughter PCBs 3 8 2 1 Upper Daughter PCB 3 8 2 2 Lower Daughter PCB 3 8 3 Middle Daughter PCB 3 8 3 1 Sample Hold Circuit 3 8 3 2 ECG Output SECTION 4 TROUBLESHOOTING AND ASSEMBLY GUIDE 4 1 4 2 4 3 4 4 INITIAL TROUBLESHOOTING PROCEDURES DETAILED TROUBLESHOOTING PROCEDURES 4 2 1 Failure Modes 4 2 2 Troubleshooting Summary 4 2 2 1 Monitor 4 2 2 2 Powerbase MONITOR DISASSEMBLY AND REASSEMBLY 4 3 1 Cover Removal 4 3 2 Power Supply PCB and Battery Charger PCB Removal 4 3 3 Front Panel Removal 4 3 4 Display PCB and Driver PCB Removal 4 3 5 Battery Removal Fuse Replacement 4 3 6 Speaker Removal 4 3 7 Cover Replacement POWERBASE DISASSEMBLY AND REASSEMBLY 4 4 1 Fuse Replacement 4 4 2 Disassembly 4 4 3 Removal 4 4 4 Reassembl
65. ecause at least one segment or indicator is missing the display or warning indicators may be incorrect Continue to use the instrument only in an urgent situation and only if the defective segment s has been identified Err 4 indicates that the N 200 lost power without going through the normal shut down procedure Turn the ON STDBY switch to STDBY and back to ON For software version 2 49 or higher Err 5 indicates jumpers W1 and W4 were not in stalled properly Contact qualified service personnel or Nellcor s Technical Service Depart ment Note The instrument will operate if any button is pressed while Err 5 is displayed Err 6 indicates that battery backed memory contents have been lost and the trend and event memories were erased and reinitialized The trend and event memories will oper ate normally as long as the N 200 is turned on but when the ON STDBY switch is set to STDBY the trend and event memories will be erased This message may indicate that the RAM socket assembly U15 needs to be replaced Contact qualified service personnel or Nellcor s Technical Service Department Note This message may also appear briefly when the N 200 is first turned on after the monitor EPROM has been replaced with a different version No action is required For software version 2 5 or higher ALL clr indicates that the trend and event memories were erased and reinitialized The N 200 erases and reinitializes the mem
66. ective Refer to Section 3 8 1 Phototransistor on power supply PCB defective Refer to Section 3 6 Note The instrument will operate if any button is pressed while Err Pb is displayed Sensor disconnected or inoperative Refer to Section 3 3 Patient module or its cable defective Refer to Section 3 3 18 V power supplies out of spec Refer to Sections 5 3 1 and 3 6 Circuit failure of the analog signal processing circuitry on the processor board Refer to Sections 5 4 and 3 4 2 A D converter circuitry failure on the proces sor board Refer to Sections 5 4 6 and 3 4 4 Defective LED drive or amplifier on proces sor board Refer to Sections 5 4 and 3 4 2 Defective red LED on the sensor Refer to Section 3 3 Defective red LED driver circuit on processor board Refer to Section 3 4 2 5 Circuit failure in the RED channel of the analog processing circuitry on the processor board Refer to Sections 5 4 5 and 3 4 2 Defective sensor or tester Refer to Section 3 3 Noisy 5 or 18 VDC power supply Refer to Sections 5 3 1 and 3 6 Partial failure of the A D conversion circuitry on the processor board Refer to Sections 5 4 6 and 3 4 4 Noisy 5 V power supply Refer to Sections 5 3 1 2 and 3 6 17 INSTRUMENT OPERATES DOES A Failure of switching circuitry in char ger TURN OFF WITH SWITCH IN STDBY board Refer to Sections 5 3 4 and 3 7 1 4 2 2 2 Powerbase Symptom Probable Diagnosis 1
67. ee daughter PCBs The mother PCB is mounted vertically at the front of the powerbase facing the monitor the daughter PCBs are mounted horizontally and mate to the mother PCB Details of instrument as sembly and disassembly are found in Section 4 SECTION 3 THEORY OF OPERATION Theory of operation is presented in two parts First a general overview of the N 200 s capabilities and the physical principles of its operation is presented Next the details of circuit operation are discussed 3 1 GENERAL THEORY The NELLCOR N 200 provides continuous noninvasive self calibrated measurements of both functional oxygen saturation and pulse rate The instrument combines the principles of spectrophotometric oximetry and plethysmography It consists of an electro optical sensor that is applied to the patient and a microprocessor based monitor that processes and displays the measurements The electro optical sensor contains two low voltage low intensity light emitting diodes LEDs as light sources and one photodiode as a light receiver One LED emits red light approximately 660 nm and the other emits infrared light approximately 920 nm When the light from the LEDs is transmitted through the tissue at the sensor site a portion of the light is absorbed by skin tissue bone and blood The photodiode in the sensor measures the light that passes through and this information is used to determine how much light was absorbed The amount of abso
68. el Gain 1 2 3 Connect the FUNCTION GENERATOR output to 013 12 RED Channel input Connect the OSCILLOSCOPE Channel 1 to TP 10 RED Channel output on the Processor PCB Verify the signal level measures 10 to 14 volts p p Remove all test equipment except the W3 jumper 5 5 8 ECG Processor 5 9 The following tests verify the correct operation of the components of the ECG signal condition ing circuits The patient module must be disconnected for these steps 1 10 11 12 13 14 15 Set the FUNCTION GENERATOR follows Function Sine Wave Frequency 10Hz Output gt Minimum Connect the FUNCTION GENERATOR ground to AGND Connect the FUNCTION GENERATOR output to the top of R65 Set the OSCILLOSCOPE as follows Channel1 0 5 V div DC Coupled Channel2 5 V div DC Coupled Sweep Rate as necessary Trigger as necessary Connect the OSCILLOSCOPE Channel 1 to the top of R65 to monitor the FUNCTION GENERATOR output Connect the OSCILLOSCOPE Channel 2 to TP 11 ECG Channel output on the Processor PCB Adjust the FUNCTION GENERATOR for an output of 16 0 1 volts p p as seen on the OSCILLOSCOPE Channel 2 Examine the OSCILLOSCOPE Channel 1 and note the amplitude Adjust the FUNCTION GENERATOR to the following frequencies Verify the amplitude of the OSCILLOSCOPE Channel 1 does not vary from that noted in step 8 and Channel 2 conforms to the listed values which
69. el is then buffered by a unity gain amplifier and low pass filtered by two active filter stages each with two poles at approximately 20 Hz The filters are slightly overdamped to improve step response The last stage in each channel is an offset amplifier with gain which offsets the signals by a small positive voltage approximately 0 25 V This voltage is derived from VREF set at 10 V and the voltage dividers R50 and R46 R80 and R74 Since the Analog to Digital Converter can only pro cess 0 to 10 V signals the positive bias provides a reference floor for analog to digital conversion stages that follow to ensure that the total chain offset errors of the op amps can never drive the outputs negative Because the RED channel has twice the gain of the IR channel the offset seen at TP10 is twice that seen at TP9 when no signal input is present 3 6 3 4 2 4 Logic Flags Several flags are produced in the analog section of the processor PCB that instruct the processor to vary circuit parameters gain and LED drive currents so that signal levels are kept safely below those which would saturate on board electronics LEDHI The SAT signal coming from the patient module can range from 8 5 V to 10 V with out saturating the patient module s analog amplifiers Comparator U20 compares the filtered and halved SAT signal to a 5 V reference When the signal drops too low SAT less than 10 V the signal is too close to the patient module s negat
70. ements from the N 200 are compared with those from another instrument it is important to consider whether the other instrument is measuring functional or fractional saturation 3 1 4 Measured vs Calculated Saturation When oxygen saturation is calculated from blood gas PaO2 the calculated value may differ from the oxygen saturation measurement of the N 200 This is because an oxygen saturation value that has been calculated from blood gas 2 has not necessarily been correctly adjusted for the effect of variables that shift the relationship between 2 and saturation These variables include temperature pH PaCO2 2 3 DPG and the concentration of fetal hemoglobin Refer to the Operator s Manual for additional information 3 2 3 2 CIRCUIT LEVEL DESCRIPTION Refer to Section 9 for the instrument schematic and block diagrams The major circuit sections consist of e the patient module e analog processing circuitry and microprocessor circuitry e front panel display logic the battery charger and power supply the instrument powerbase which contains the data communications interface circuitry Since the measurement of oxygen saturation requires light of two different wavelengths two LEDs IR and are used to generate light which is passed through the tissue at the sensor site into a single photodiode The LEDs are illuminated alternately with a four state clock The photodiode signa
71. er PCB 8085 processor U5 is driven by a 6 144 MHz crystal A watchdog timer comprised of U6 C7 CR1 R5 Q1 R6 and C8 monitors the Serial Output Data SOD signal from U5 pin 4 If SOD does not produce a positive pulse within any 100 ms period the watchdog timer sets the trap pin U5 6 which causes the 8085 to reset to address 0 Delay circuit CR2 R9 and C10 provides reset on power up Addresses presented on the multiplexed address data bus of U5 are held by latch U2 when ALE U5 pin 30 pulses high 16 kbyte EPROM U4 is mapped starting at address 0 and 8 kbyte RAM U3 is mapped starting at HEX 4000 I O for the upper daughter PCB is memory mapped Addresses are decoded on the lower daughter PCB Buffer U1 reads several digital signals Four switches S1 through S4 51 S2 ZERO and FULL set zero and full scale on all analog outputs S3 TREND initiates a TREND printout S4 EVENT initiates an EVENT printout Jumpers W1 and W2 which when installed place the system in various diagnostic modes SCALE which is the output of switch SW1 SCHEMATIC MIDDLE DAUGHTER POWERBASE sets the SAT analog output range 0 100 or 50 100 ECGTRIG which is generated with every R wave when external ECG monitor is used SCHEMATIC MIDDLE DAUGHTER PCB POWERBASE U7 pin 7 3 8 2 2 Lower Daughter PCB U6 and U7 provide address decoding for all devices in the powerbase I O functions begin at HEX 8000 Timer circu
72. ernal ECG signal appears 3 8 3 1 Sample Hold Circuit Bus compatible 8 bit DAC U5 is provided with a reference voltage of approximately 10 V by nega tive voltage regulator U6 Potentiometer R11 trims the output voltage of U1 pin 6 to 10 00 0 02 V when DAC gain is set to maximum the U1 U5 combination inverts the reference voltage Switch SW1 selects a full scale analog output voltage of 1 V or 10 V by switching in the voltage divider formed by R2 R5 and R6 U4 is a 1 to 8 bus compatible analog demultiplexer DAC output at U4 pin 9 feeds through to the selected output U4 pin 5 6 7 or 8 Each output drives a separate sample hold circuit made up of storage capacitors C4 through C7 and FET input operational amplifiers U2 and U3 Zener diodes at the outputs of the sample hold amplifiers protect against external short lived transients 1 kohm output resistors quell oscillations which may occur when driving highly capacitive loads 3 8 3 2 ECG Output The ECG sample hold channel is bidirectional It differs from the other three channels in that the output signal is AC coupled at a corner frequency of 0 5 Hz to unity gain buffer U2 Resistor R12 buffers the output of the unity gain buffer when signals enter the ECG bidirectional port 3 Incoming ECG signals are AC coupled through C16 and R25 to two parallel circuits unity gain buffer a peak follower circuit composed of U2 9 C17 R27 and U3 with slow decay
73. errupt normal software operation while the instrument is in use 5 5 1 Processor PCB Voltage Regulation 5 6 5 5 2 5 5 3 This test verifies voltage regulation of the Processor PCB on board regulators VR1 15 VR2 15 VR3 5 and VR4 5 1 Place the ON STDBY switch the ON position 2 Connect the DMM lead to AGND the Processor PCB 3 Connect the DMM lead to the VR1 output lead The DMM must read 15 00 0 750 volts 14 250 to 15 750 4 Connect the DMM lead to the VR2 output lead The DMM must read 15 00 0 750 volts 14 250 to 15 750 5 Connect the DMM lead to the VR3 output lead The DMM must read 5 00 0 250 volts 4 750 to 5 250 6 Connect the DMM lead to the VR4 output lead The DMM must read 5 00 0 250 volts 4 750 to 5 250 7 Disconnect all test equipment except the jumper W3 Calibration Resistor Determination The following test will verify the operation of the Sensor Calibration Resistor determination circuit and required microprocessor involvement Known values of resistance are placed across the circuit input and the resulting index voltages are measured 1 Connect the 6040 OHM 1 0 TEST RESISTOR from U27 10 on the Processor PCB to AGND Alternate method is to place the resistor across pins 1 and 6 of the patient module if it is plugged in to the N 200 2 Using the N 200 Control Knob select memory location 9 in the OXYGEN SATURATION
74. ersonnel or Nellcor s Technical Services Department 3 The instrument operates on AC power but the BATT IN USE indicator is always on The powerbase is disconnected from the monitor The instrument is not receiving AC power because the power cord is defective is connected or is connected to a defective AC outlet Replace the power cord connect to AC power or try another AC outlet AC fuse on the rear panel is defective Replace the fuse see Section 4 4 1 4 The instrument displays an error message Err 1 indicates defective RAM data memory See Section 3 4 1 1 Err 2 indicates defective ROM program memory See Section 3 4 1 1 Err 3 indicates a damaged display or indicator See Sections 4 3 4 3 5 1 4 WARNING The instrument will operate if any button is pressed while Err 3 is showing However because at least one segment or indicator is missing the display or warning indicators may be incorrect Continue to use the instrument only in an urgent situation and only if the defective segment s has been identified Err 4 indicates that the N 200 lost power without going through the normal shut down procedure Turn the ON STDBY switch to STDBY and back to ON For software version 2 49 or higher Err 5 indicates jumpers W1 and W4 were not in stalled properly Contact qualified service personnel or Nellcor s Technical Service Depart ment Note The i
75. g circuit set the OSCILLOSCOPE as follows Channel 1 2 V div DC Coupled Sweep Rate 5 0 ms div Trigger Line auto Connect the OSCILLOSCOPE ground to AGND Connect the OSCILLOSCOPE Channel 1 to U20 pin 15 and verify that the indicated square wave syncs with the 60 Hz line has a period of 16 ms and an amplitude of about 4 volts p p This verifies the operation of the line frequency sampling circuit Disconnect all test equipment except the W3 jumper A D D A Alignment These tests verify the correct operation of the multiplexer automatic offset control and digitizing circuitry 1 Set up the following memory locations as specified 190 1 195 7 196 8 197 0 198 0 Connect the DMM lead of a 4 1 2 digit DMM to AGND on the Processor PCB Connect the DMM lead to TP 2 on the Processor PCB Adjust R117 on the Processor PCB for a reading of 0 0000 on the DMM Connect the DMM lead to TP 3 on the Processor PCB Read and record any offset voltage and its polarity at TP 3 on the Processor PCB Connect the DMM lead to TP 1 on the Processor PCB Set memory location 195 6 Note that the DMM now indicates around 10 volts Record the exact voltage Algebraically add the voltages recorded at TP 1 step 8 and 3 step 6 10 11 12 13 14 15 16 17 18 Example 1 TP 3 voltage step 6 0 017 volts b TP 1 voltage in step 8 9 997 volts c The algebraic sum will be 9
76. imately 50 mA 3 7 3 4 3 Refer to SCHEMATIC PROCESSOR SHEET 3 in the following discussion 3 4 3 1 Active Filters The ECG signal from the patient module is conditioned by 5 stages of active filtering The total gain of the chain of active filters is approximately 32 The EGG is first low pass filtered by U12 and associated circuitry The two filter poles are set at 40 Hz and the gain is equal to 1 U6 is a switched capacitor notch filter with a gain of 0 32 Capacitor switching frequency NCLK is derived from timer U34 PROCESSOR PCB SHEET 1 and is set by the processor to remove AC power line interference See Section 3 4 3 4 Power Line Frequency Sensing A second 2 pole 40 Hz low pass filter follows the notch filter This filter removes the switching transients inherent in switched capacitor filter U6 A high pass filter U12 with gain of 101 and cutoff frequency 0 5 Hz follows the second low pass stage Because this filter stage has a long time constant a processor control ECGZERO resets the filter by discharging the filter capacitors Reset occurs under the following conditions if a lead comes loose from the patient or the ECG signal is contaminated by patient muscle contrac tions the ECG signal baseline can be driven into a railed condition This occurs because of the high approximately 1000 combined gain of the patient module and ECG front end filters When the ECG base
77. it U4 generates the real time interrupt RST7 5 U4 pin 10 U4 also produces the baud rates for UARTs U2 and U5 U5 drives the powerbase side of the monitor powerbase optical link at 19 2 kbaud Circuit elements associated with U5 provide signal conditioning for transmitting and receiving on the optical communication link The link s LED and phototransistor are shown on the SCHEMATIC MOTHER PCB POWERBASE drawing U5 pin 23 RTS is set low in software when the instrument is in an alarm condition producing a logic high on U8 11 ALMOUT UART U2 drives the external RS232 interface and the fiber optic output CR1 Level translator U3 performs the voltage level shift required for the TTL RS232 interface RXxRDY 02 pin 14 is returned to the main processor as RST5 5 Baud rates for both UARTs are derived from timer U4 pins 13 and 17 Buffer U1 reads 8 bit DIP switch S1 which is used to select the baud rate and data transmission format Connector J8 is a 9 pin miniature D type for the RS232 data link 3 8 3 Middle Daughter PCB The middle daughter board shown on SCHEMATIC MIDDLE DAUGHTER PCB POWERBASE contains all of the analog circuitry for the powerbase For purposes of discussion the board can be divided into two portions the sample hold circuit with its associated DAC and analog demultiplexer the ECG input circuit with self adjusting threshold This circuit triggers processor U5 on the upper daughter board whenever an ext
78. itry on the processor board Refer to Sections 5 4 5 and 3 4 2 Defective sensor or tester Refer to Section 3 3 Noisy 5 or 18 VDC power supply Refer to Sections 5 3 1 and 3 6 Partial failure of the A D conversion circuitry on the processor board Refer to Sections 5 4 6 and 3 4 4 Noisy 5 V power supply Refer to Sections 5 3 1 2 and 3 6 17 INSTRUMENT OPERATES DOES A Failure of switching circuitry in char ger TURN OFF WITH SWITCH IN STDBY board Refer to Sections 5 3 4 and 3 7 1 4 2 2 2 Powerbase Symptom Probable Diagnosis 1 NO ANALOG OR DIGITAL OUTPUTS A AC power disconnected B Picofuse blown on mother PCB Refer to Section 3 8 1 C Faulty transformer Refer to Section 3 8 D Digital circuitry on upper or lower daughter boards Refer to Section 3 8 2 2 FULL SCALE AND ZERO SWITCHES Phototransistor on mother PCB defective WORK BUT NO ANALOG OUTPUTS Refer to Section 3 8 1 MONITOR INFORMATION DOES NOT LED on monitor power supply board APPEAR ON DIGITAL OUTPUTS defective Refer to Section 3 6 3 TREND EVENT FUNCTIONS A AC power disconnected INOPERATIVE EXTERNAL LED on mother PCB defective Refer to ECG INOPERATIVE ADULT Section 3 8 1 NEONATE ALARM SWITCH Phototransistor on power supply PCB INOPERATIVE defective Refer to Section 3 6 4 NOORINCORRECT DIGITAL OUTPUT A Baud rate mismatch between power base and output device Refer to N 200 Operator s
79. ive power rail This condition sets the LEDHI flag which interrupts the processor The processor then reduces the LED drive currents to avoid signal saturation INAMPHI Following the INAMP programmable gain section another comparator 020 gener ates the INAMPHI interrupt This circuit compares the signal to a 10 V reference When the INAMP gain is set too high the signal level exceeds 10 V and the INAMPHI flag is set The processor then reduces the gain of the INAMP stage to lower the signal level LEDLOW Ifa sensor is exposed to bright light the output of the patient module is driven nega tive an amount proportional to the ambient light exposure This condition occurs because the ambient light causes an increase in the photodetector current from the sensor The converter in the patient module converts the increased current to a negative voltage When comparator U20 senses negative going voltage signals more positive than its 5 V reference it sets LEDLOW high The processor polls the LEDLOW flag and increases drive current to the LEDs when LEDLOW is high for improved S N ratio This condition occurs when the patient removes the sensor from high ambient light exposure A delay of up to 30 seconds is provided to prevent the LED current from changing in frequently changing ambient light conditions The delay is implemented by passing the SAT signal through a fast attack slow decay circuit formed by R95 R96 C74 CR8 and U27 before it r
80. l representing light from both LEDs in sequence is amplified and then separated by a two channel synchronous detector one channel sensitive to the infrared light waveform and the other sensitive to the red light waveform These signals are then filtered to remove the LED switching frequency as well as electrical or ambient noise and then digitized by an analog to digi tal A D converter This digital signal is then processed by the microprocessor to identify individual pulses and compute the oxygen saturation from the ratio of the pulse seen by the red wavelength compared to the pulse seen by the IR wavelength Throughout this section and on the schematics active low logic signals are designated by an over bar above the signal name for example SIGNAL 3 3 PATIENT MODULE The patient module contains preamplifiers for the saturation SAT and electrocardiogram ECG signals refer to SCHEMATIC PATIENT MODULE PCB Power for the circuitry is 15 V generated by the processor board The drive current for the pair of sensor LEDs is supplied from the instrument generated on the processor board VIR and VRED on SCHEMATIC PROCESSOR PCB SHEET 4 This waveform is a bipolar current drive which is passed through the patient module to the back to back sensor LEDs A positive current pulse drives the IR LED and a negative current pulse drives the red LED The drive current is controlled by a feedback loop on the processor board in response to
81. lar line Observe all instructions warnings and cautions in the N 200 Operator s Manual and in the directions for sensor use The oxygen saturation measurement of the N 200 does not correlate with a value measured by a laboratory CO Oximeter Fractional measurements have not been converted to functional measurements before the comparison was made The NELLCOR N 200 like other two wavelength oximeters measures functional saturation Multi wavelength oximeters such as the IL282 CO Oximeter and Corning oximeters measure fractional saturation Fractional measure ments must be converted to functional measurements for comparison The equation used to make this conversion can be found in Section of the N 200 Operator s Manual The OXYGEN SATURATION display is erratic and the ECG LOST display is flashing Excessive patient motion has caused the ECG electrodes to become displaced dislodged or disconnected from the ECG cable check the position of the electrodes and check the connections ECG cable has come loose from the patient module connector check the connection If the ECG signal is coming from a bedside ECG monitor the ECG input cable may have become dislodged from the ECG IN OUT connector on the rear of the N 200 or from the bedside monitor check the connection 15 Trend and event data are not available 16 17 memory back up battery has been discharged e The trend and eve
82. libration resistor and then checked That calibration resistor is read by the N 200 software to determine the calibration coefficients that are used for the measurements obtained by that sensor The N 200 is automatically calibrated each time it is turned on at periodic intervals thereafter and when a new sensor is connected Also the intensity of each LED in the sensor is adjusted auto matically to compensate for differences in tissue thickness 3 1 3 Functional vs Fractional Saturation Because the N 200 measures functional oxygen saturation it may produce measurements that dif fer from those of instruments that measure fractional oxygen saturation Functional oxygen saturation is defined as oxygenated hemoglobin expressed as a percentage of the hemoglobin that is capable of transporting oxygen Because the N 200 uses two wavelengths to measure saturation it measures only oxygenated and deoxygenated i e functional hemoglo bin It does not detect the presence of significant amounts of dysfunctional hemoglobin such as carboxyhemoglobin or methemoglobin In contrast some other laboratory instruments such as the IL 282 CO Oximeter report fractional oxygen saturation values Fractional saturation is defined as oxygenated hemoglobin expressed as a percentage of total hemoglobin whether or not that hemoglobin is available for oxygen transport Dysfunctional hemoglobin species are included in this calculation Consequently when measur
83. line rises too much the processor temporarily brings ECGZERO low to reset the filter 3 4 3 2 Offset Amplifier An offset amplifier U12 biases the filtered ECG signal by 5 V so that the A D converter can digi tize the entire waveform the A D converter can only process positive analog signals The output of the offset amplifier ECG is digitized by the A D converter and provided as a data output by the powerbase 3 4 3 3 Detached Lead Indicator 3 stage circuit composed of absolute value amplifier U5 voltage comparator U4 and D type flip flop U3 generates the LEADOFF flag The circuit examines the condition of the ECG signal at the input to the switched capacitor notch filter U6 after it has undergone one stage of lowpass filtering A detached lead is sensed as follows within the patient module a biasing resistor network drives the ECG signal to one of the supply rails 15 if one or both ECG signal leads becomes detached from the patient If the signal is driven to the negative supply rail it is converted to a positive voltage by absolute value amplifier U5 The output of this circuit is compared to a 10 V reference by comparator U4 A voltage in excess of 10 V drives the output of U4 low setting and latching flip flop U3 through NAND gate U10 When the flip flop has latched the LEADOFF logic signal is set high notifying the processor that a lead has come loose When the processor polls LEADOFF and discovers that it is a
84. lt for the instrument to find a pulse pattern use C LOCK ECG synchronization or 4 4 12 13 14 if possible ask the patient to remain still check whether the sensor is securely applied and replace it if necessary or use a type of sensor that tolerates more patient motion or move the sensor to a site with less movement or use Mode 3 if appropriate refer to the N 200 Operator s Manual The patient has a pronounced dicrotic notch which causes the pulse rate to double Try another sensor site An artifact is present on the ECG monitor Refer to the manual for that monitor An electrocautery unit is interfering refer to item number 8 Oxygen saturation measurement does not correlate with the value calculated from a blood gas determination The calculation has not been correctly adjusted for the effects of pH temperature 2 2 3 DPG or fetal hemoglobin In general calculated saturation values are not reliable as correlative measurements check to see that the calculations have been corrected for relevant variables For more information see Section 3 1 4 Accuracy can be affected by incorrect sensor application or use significant levels of dysfunctional hemoglobins intravascular dyes bright light excessive patient movement venous pulsations electrosurgical interference and placement of a sensor on an extremity that has a blood pressure cuff arterial catheter or intravascu
85. mbly views 8 3 circuit boards location 2 2 4 10 4 11 4 15 removal 4 11 4 13 4 15 C LOCK ECG synchronization 3 1 clock calendar battery 5 12 clock generator 3 5 CLRLO signal 3 9 control knob 3 12 D D A conversion 3 10 DACMP signal 3 11 data outputs failure 4 10 4 11 demultiplexer 3 6 description of instrument 2 1 detached lead 3 8 dicrotic notch 4 5 digit display drivers 3 11 3 12 DIGIT signals 3 12 digital output failure 4 10 4 11 display erratic 4 3 Display PCB 3 11 3 13 removal 4 13 DISPLAY signal 3 12 DP signal 3 12 drive current LED 3 3 Driver PCB 3 11 removal 4 13 E ECG circuitry 3 8 3 17 3 18 ECG output powerbase 3 18 ECG processor 5 9 5 10 5 11 ECG signal 3 3 3 8 3 9 3 17 3 18 EGC LOST indicator 4 4 ECGLOST signal 3 12 ECGON signal 3 12 ECGTRIG signal 3 16 3 18 ECGZERO signal 3 8 electrocautery interference 4 4 error messages ALL clr 4 2 4 9 Err 1 4 1 4 8 Err 2 4 1 4 8 Err 3 4 1 4 8 Err 4 4 2 4 8 Err 5 4 2 4 8 Err 6 4 2 4 8 Err Pb 4 2 4 9 event data not available 4 6 print failure 4 6 EVENT signal 3 16 F failure modes 4 6 flag signals 3 7 3 10 3 11 fractional saturation 3 2 front panel controls 2 1 3 12 display 3 11 removal 4 12 functional saturation 3 2 fuse replacement 4 13 4 14 G GROUND signal 3 9 H heart activity 3 1 HIRATE signal 3 12 HISAT signal 3 12 input amplifier
86. nd the AUDIO ALARM OFF buttons While holding the buttons in adjust the front panel control knob until the OXYGEN SATURATION display reads memory location 24 Examine the PULSE RATE display and verify that it reads between 32 and 44 This reading is the Input Amplifier gain setting If the N 200 meets all of the above tests disconnect the test equipment not the patient module and pocket tester and continue with the following steps If the preceding steps are not met the instrument is not functioning properly and must be repaired 5 7 5 Adjusting Alarm Limits 1 Record the number displayed the OXYGEN SATURATION window Press and hold the LOW SAT button and slowly turn the control knob counter clockwise Verify that the LOW SAT indicator goes out when the OXYGEN SATURATION display reaches the number noted in the beginning of this step Continue turning the control knob until the value in the OXYGEN SATURATION window is 75 or less Record the number displayed in the PULSE RATE window Press and hold the LOW RATE button and slowly turn the control knob counter clockwise Verify that the LOW RATE indicator goes out when the PULSE RATE display reaches the number noted in the beginning of this step Continue turning the control knob until the value in the PULSE RATE window is 40 or less 5 15 5 7 6 5 7 7 5 7 8 5 7 9 5 Press and hold the SAT button and turn the control knob counter clockwise Verify that when the
87. nformation used during trend and event recording as well as battery back up to prevent data loss when the instrument is in standby Processor U8 pins 9 through 16 designated ADO AD7 are multiplexed to alternately present the low order address byte and a data byte On the first clock cycle of an instruction an address is present on these lines The ALE signal U8 pin 25 pulses high to latch the lower byte of the ad dress in transparent octal latch U33 In the following clock cycles data can flow bidirectionally on these lines The upper 4 address lines of U8 A16 through A19 are also multiplexed alternately carrying address and status information Only the uppermost bit A19 is used in the N 200 for address de coding This pin U8 pin 35 is at logic high when the system is addressing ROM space and low when it is addressing RAM or performing input output I O functions The processor s ALE signal latches this bit in flip flop U3 3 4 3 4 1 2 The entire processor system is memory mapped That is all devices on the 8088 data bus cessed read from or written to at specific memory locations in the 1 Mbyte memory range The upper 512 kbytes of memory are considered ROM space the lower 512 kbytes are con sidered RAM and I O space ROM resides in the top 64 kbytes of memory with the program starting at hex FFFFO after reset Since only 64 kbytes of the ROM space are actually used im ages of the
88. ns 2 2 4 11 4 13 removal 4 11 4 13 4 15 PLSSRCHHI signal 3 12 PLSSRCHLO signal 3 12 pocket tester operation 5 14 5 15 power line frequency sensing 3 9 power supply board map 5 19 noise 5 5 power supply PCB 3 13 removal 4 11 4 12 testing and calibration 5 5 5 6 powerbase alignment 5 12 5 13 description 2 2 disassembly 4 15 reassembly 4 15 theory of operation 3 15 troubleshooting summary 4 10 powerbase to monitor communication 5 16 power on display element test 3 13 time delay 3 15 processor board test map 5 20 processor PCB 3 4 processor PCB tests A D D A alignment 5 11 5 12 calibration resistor determination 5 7 ECG processor 5 9 5 10 5 11 Input amplifier INAMP automatic gain 5 8 IR channel gain 5 9 LED intensity control 5 7 processor PCB voltage regulation 5 6 5 7 RED channel gain 5 9 sync detector alignment 5 8 processor PCB voltage regulation 5 6 5 7 processor theory of operation 3 4 PSEN signal 3 14 pulse rate and ECG monitor correlation 4 4 4 5 no display 4 2 4 9 pulse width modulator 3 13 5 3 1 RED Channel Gain verification 5 9 RED signal 3 7 3 9 REDGATE signal 3 6 RST5 5 signal 3 17 RST7 5 signal 3 17 RWTHRESHOLD signal 3 10 RxRDY signal 3 11 3 17 5 SIN ratio 3 6 safety features 2 1 sample hold circuit 3 17 SAT signal 3 3 3 6 3 7 SATINVERT signal 3 6 saturation calculated 3 2 fractional 3 2
89. nstrument will operate if any button is pressed while Err 5 is displayed Err 6 indicates that battery backed memory contents have been lost and the trend and event memories were erased and reinitialized The trend and event memories will oper ate normally as long as the N 200 is turned on but when the ON STDBY switch is set to STDBY the trend and event memories will be erased This message may indicate that the RAM socket assembly U15 needs to be replaced Contact qualified service personnel or Nellcor s Technical Service Department Note This message may also appear briefly when the N 200 is first turned on after the monitor EPROM has been replaced with a different version No action is required For software version 2 5 or higher ALL clr indicates that the trend and event memories were erased and reinitialized The N 200 erases and reinitializes the memories if the data have been corrupted The memories can also be manually cleared and reinitialized In both cases the ALL clr appears No further action is necessary When ALL clr appears because the memory data were corrupted and erased a simultaneous 5 second alarm sounds Note If the N 200 erases the trend and event memories a message header appears on the trend graph indicating that the oldest portion of the memory was erased For software version 2 5 or higher Err Pb indicates the powerbase is not communicat ing with the monitor Check that th
90. nt memory has been erased Trend or event data cannot be printed Switch settings are incorrect check the switch settings see N 200 Operator s Manual Cables are improperly connected check the cable connections The NELLCOR N 9000 recorder interface cannot be used e switch settings are incorrect check the switch settings see N 200 Operator s Manual 4 2 DETAILED TROUBLESHOOTING PROCEDURES 4 2 1 Failure Modes Instrument failures can be broadly divided into two classes An outright failure of a component in one of the instrument modules will cause consistently incorrect operation or no operation at all Use the Troubleshooting Summary below as a guide to diagnosing these failures Subsequent sections dealing with repairs to each specific module can then be used to correct the diagnosed problem The second more difficult problem deals with intermittent noisy or out of spec perform ance of the instrument While these problems may also be related to a component failure they can also be caused in some cases by noise in the environment such as electro cautery or Bovie interference an improperly functioning sensor or misapplication of the sensor by the user If an instrument is suspected of having substandard performance the procedures outlined in Section 5 Testing and Calibration should be followed to help diagnose the problem WARNING The procedures in this section require tests and adju
91. o steps first loosen each screw part way then go back and remove each screw completely Note that the screws may remain in their holes held by the plastic standoffs between the PCBs 5 Remove the display and driver PCBs as one unit The PCBs are assembled with component sides exposed for easy troubleshooting access It is recommended that they not be separated unless replacement of one of the PCBs is required If necessary separate the two PCBs by decoupling connectors J6 and J4 then separate the PCBs by carefully prying the two snap in standoffs apart beginning at one end of the two board assembly 4 3 5 Battery Pack Removal Fuse Replacement The battery pack can be removed with the instrument front panel in place 1 The in line fuse holder and negative lead from the battery pack are secured to aclip by a tie wrap Cut this tie wrap to free the battery cables For fuse replacement untwist halves of in line fuse holder and replace fuse with one of same type and rating 2 Remove the two screws from the battery retaining clip and lift out the battery pack 4 3 6 Speaker Removal To remove the speaker detach the speaker connector and remove the four speaker mounting screws 4 3 7 Top Cover Replacement Refold the connector cables to their original contours so that the top cover fits securely without be ing forced Take care that cables do not interfere with bosses or other obstructions on the cover In 4 13 particular make sure
92. of RAM memory on the processor board diagnosed during power up test Refer to Sections 5 4 and 3 4 1 Failure of ROM memory on the processor board diagnosed during power up test Refer to Section 5 4 and 3 4 1 Failure of an LED segment or lamp diagnosed during power up test Refer to Section 3 5 1 4 18 V power supplies out of spec Refer to Sections 5 3 1 and 3 6 Failure of D A conversion circuitry on the processor board Refer to Sections 5 4 6 and 3 4 4 Loss of power without going through normal shut down procedure Refer to Section 3 7 1 Turn ON STDBY switch to STDBY and back to ON ON STDBY switch is damaged Instrument is inoperative on battery Refer to Section 5 3 Jumpers W1 and W4 not installed properly Note The instrument will operate if any button is pressed while Err 5 is displayed Battery backed memory contents lost trend and event memories erased and reinitialized Memories will operate normally while N 200 is turned on but when N 200 is turned to STDBY memory contents will be erased This error message may indicate that RAM socket assembly U15 needs to be replaced Refer to Section 5 5 10 Err 6 may also briefly appear when N 200 is first turned on after monitor EPROM has been replaced with a different version No action required 11 12 13 14 15 16 INSTRUMENT OPERATES SHOWS ALL clr INSTRUMENT OPERATES SHOWS Err Pb INSTRUMENT OPERATES NO
93. onnect a 1 000 ohm resistor across the DMM leads to improve measurement stability Connect the DMM lead to the BATT terminal on the Battery Charger PCB Connect the DMM lead to R4 end pointing toward the rear of the N 200 on the Battery Charger PCB This is a convenient location for the BATT terminal connection Connect the AC power cord to the N 200 The DMM must indicate an open circuit voltage of 7 1 0 02 7 2 0 002 If the voltage is out of tolerance adjust R12 R12 is located in approximately the center of the Battery Charger PCB Connect the 10 ohm 2 watt load resistor across the DMM measurement points The DMM indication must drop to 3 75 0 50 2 50 0 50 volts If the voltage drop is not observed the current limit circuit is defective Place the ON STDBY switch in the STDBY position Low Battery Instrument Shut off Voltages These tests will verify the operation of FET Q1 associated components and microprocessor operation with regard to power control 5 3 5 3 4 1 Disconnect the 200 AC power cord 2 Adjust the DC POWER SUPPLY to 0 VDC 3 Connect the DC POWER SUPPLY lead to the BATT terminal on the Battery Charger PCB 4 Connect the DC POWER SUPPLY lead to R4 end pointing toward the rear of the N 200 on the Battery Charger PCB This is a convenient location for the BATT terminal 5 Connect the DMM lead to AGND on the Processor PCB 6 Connect the DMM lead to the cathode bar end
94. ories if the data have been corrupted The memories can also be manually cleared and reinitialized In both cases the ALL clr appears No further action is necessary When ALL clr appears because the memory data were corrupted and erased a simultaneous 5 second alarm sounds Note If the N 200 erases the trend and event memories a message header appears on the trend graph indicating that the oldest portion of the memory was erased For software version 2 5 or higher Err Pb indicates the powerbase is not communicat ing with the monitor Check that the powerbase is plugged in and the monitor is correctly installed on the powerbase If the message does not disappear contact qualified service personnel or Nellcor s Technical Service Department Note The instrument will operate if any button is pressed while Err Pb is displayed 5 Perfusion indicator is not tracking pulse PULSE SEARCH indicator is on and saturation and pulse rate are not displayed The sensor is improperly applied to the patient or it is not plugged in Check and correct if necessary The patient s perfusion is too poor for the instrument to detect an acceptable pulse check the condition of the patient use C LOCK ECG synchronization test the instrument on yourself or another patient try the nasal OXISENSOR R 15 The sensor is damaged Replace with another sensor The patient module is damaged Try another patient mo
95. r J3 from the Processor PCB Invoke the diagnostic loop 190 1 See page 1 of this section for details Set the FUNCTION GENERATOR as follows Waveform Sine Frequency 10 0 Hz Amplitude 2Vp p Connect the FUNCTION GENERATOR ground to AGND on the Processor PCB Connect the FUNCTION GENERATOR output to TP 6 on the Processor PCB Set the OSCILLOSCOPE as follows Channel 1 5 V div DC Coupled Channel 2 2 V div DC Coupled Sweep Rate 10 msec div Trigger Channel 1 auto Connect the OSCILLOSCOPE ground to AGND on the Processor PCB Connect the OSCILLOSCOPE Channel 1 to TP 7 on the Processor PCB Select memory location 193 Depress AUDIO ALARM and LOW SAT buttons and set the value of location 193 to 0 The displayed sine wave will be lt 1 volt p p Slowly increase the value of location 193 and notice that the amplitude of the sine wave will increase When the value of location 193 reaches approximately 150 the displayed sine wave amplitude will saturate at approximately 30 volts p p this represents the 15 volt opamp rails Adjust location 193 value to 0 Connect the OSCILLOSCOPE Channel 2 input to U20 pin 2 Note that Channel 2 displays TTL level of approximately 0 volts Slowly increase the value of 193 until the Channel 1 waveform reaches approximately 20 volts p p Continue to increase the value and notice that there will be a positive pulse appear on Channel 2 which corresponds to the the area of th
96. r PCB Powerbase Assembly 9 24 Block Diagram Oximeter 9 25 Timing Diagram Oximeter 9 26 Cable Interconnect Diagram Monitor 9 27 Cable Interconnect Diagram Powerbase 9 28 SECTION 10 INDEX A AC operation test 5 13 AC signal 3 9 3 11 active filter ECG signal 3 8 A D D A alignment 5 11 5 12 conversion 3 3 3 6 3 9 3 10 alarm condition 3 17 alarm limits institutional 6 1 adjusting 5 15 adult neonatal 5 14 alarm silencing disabling 5 16 temporary 5 16 ALE signal 3 4 3 16 aligning A D D A 5 11 powerbase 5 12 sync detector 5 8 ALMINH signal 3 12 ALMOUT signal 3 17 analog front end 3 6 analog output failure 4 10 analog section 3 6 B bargraph display drivers 3 11 BARGRAPH signals 3 12 BATLO signal 3 12 BATON signal 3 12 battery pack removal 4 15 battery charger board test point map 5 19 circuit 3 15 testing and calibration 5 2 5 3 5 4 5 5 theory of operation 3 14 3 15 battery charger PCB 3 14 removal 4 11 battery charger PCB tests battery charging voltage 5 3 battery operation 5 5 low battery instrument shut off voltages 5 3 5 4 ON STDBY switch test 5 4 raw DC voltage AC and battery operation 5 2 5 3 battery charging voltage 5 3 battery operation test 5 5 5 14 baud rates 3 5 3 17 BUTTON signals 3 12 calculated saturation 3 2 calibration 5 1 theory of automatic 3 2 calibration resistor determination 5 7 chassis level asse
97. re 4 1 leaving all internal connecting cables in place Hold the spring loaded latches located at the back of the monitor securely in the bottom cover while the top cover is being removed If the latches come out reassemble them in 4 10 the bottom cover In its opened condition with all cables connected the instrument may be operated normally for calibration and troubleshooting Figure 4 1 shows the placement of PCBs within the top and bottom covers The processor PCB is on the top cover held with two screws There are two washers under each screw The power supply PCB is on the back edge of the instrument The battery charger PCB is on the left side Fig 4 1 Monitor PCB locations 4 3 2 Power Supply PCB and Battery Charger PCB Removal The power supply PCB and battery charger PCB can be removed after the instrument top cover has been removed Remove the two PCBs as a set by performing the following steps 1 Disconnect all cables on the processor PCB some connectors have retaining clips which must be removed first Cut the tie wrap holding the large electrolytic capacitor on the power supply PCB Disconnect the 2 conductor power cable from the display driver PCB For reassembly verify that the red lead is on top Disconnect the battery leads and switch connector from the battery charger PCB For reassembly verify that the red battery lead connects to the BATT terminal the black bat 4 11 tery lead
98. represent the ECG processing circuit bandpass limits Frequencies in Hertz Channel 2 limits in volts p p 0 5 3 10 0 6 1 40 0 11 3 50 0 3 Slowly adjust the FUNCTION GENERATOR from 50 to 70 Hz and notice that the OSCIL LOSCOPE Channel 2 indicates the action of the 60 Hz Notch Filter by a complete amplitude reduction or a null at 60 Hz The final positive offset stage of the ECG Channel can be qualified by adjusting the FUNCTION GENERATOR to 10 Hz and noting that the majority of the signal on the OSCILLOSCOPE Channel 2 is above zero about 80 Disconnect all test equipment except the W3 jumper To test the detached lead detector circuit set the DC POWER SUPPLY to 15 volts Connect the DC POWER SUPPLY lead to AGND Connect the DMM lead to AGND 5 10 5 5 9 16 17 18 19 20 21 22 Remove instrument from diagnostic loop by setting 190 0 Connect the DMM lead to U3 pin 9 the LEADOFF flag generator The DMM must read approximately zero volts If the DMM indicates around 5 volts barring circuit malfunction it probably means that the Detached Lead Detector Circuit has been triggered by some extraneous influence This condition can be remedied by momentarily grounding R65 Touch the DC POWER SUPPLY lead to the top of R65 for a moment and verify the DMM now indicates approximately 5 volts This verifies that the Detached Lead Detector Circuit is functioning To test the line frequency samplin
99. rption remains essentially constant during the diastolic nonpulsatile phase and is analogous to the reference measurement of a spectrophotometer With each heart beat a pulse of oxygenated arterial blood flows to the sensor site This oxygen ated hemoglobin differs from deoxygenated hemoglobin in the amount of red and infrared light that it absorbs The N 200 continuously measures absorption of both red and infrared light and uses those measurements to determine the percentage of functional hemoglobin that is saturated with oxygen When the pulsatile blood is present the light absorption at both wavelengths is changed by the presence of that blood The NELLCOR N 200 then corrects the measurements during the pulsa tile flow for the amount of light absorbed at the initial measurements The ratio of the corrected absorption at each wavelength is then used to calculate functional oxygen saturation 3 1 1 C LOCK ECG Synchronization When the N 200 is provided with ECG input it is receiving two signals that independently reflect cardiac activity one from the sensor and the other from the ECG This enhances the performance of the instrument in the presence of patient movement as discussed below There is a time delay between the electrical and mechanical activity of the heart When an ECG QRS complex is detected a pulse will be detected at the sensor site a short time later The length of this delay varies with the heart rate the patient s phy
100. s discharged Connect to AC power If the problem persists check the AC fuse If this does not resolve the problem contact qualified service personnel or Nellcor s Technical Service Department 2 The instrument operates on AC power but not on the battery battery is discharged Fourteen hours are required to completely recharge the battery battery pack is defective or the battery fuse is open Contact qualified service personnel or Nellcor s Technical Service Department battery charger is defective Contact qualified service personnel or Nellcor s Technical Services Department 3 The instrument operates on AC power but the BATT IN USE indicator is always on The powerbase is disconnected from the monitor The instrument is not receiving AC power because the power cord is defective is connected or is connected to a defective AC outlet Replace the power cord connect to AC power or try another AC outlet AC fuse on the rear panel is defective Replace the fuse see Section 4 4 1 4 The instrument displays an error message Err 1 indicates defective RAM data memory See Section 3 4 1 1 Err 2 indicates defective ROM program memory See Section 3 4 1 1 Err 3 indicates a damaged display or indicator See Sections 4 3 4 3 5 1 4 WARNING The instrument will operate if any button is pressed while Err 3 is showing However b
101. s through a 50 kHz low pass filter one quarter of quad operational amplifier U27 in a 2 pole Butterworth configuration The signal is then AC coupled to another U27 op amp configured as a gain stage with unity gain A variable attenuator composed of Digital to Analog Converter DAC 044 and amplifier 032 is followed by noninvert ing amplifier U32 with gain of 51 Together the two circuits provide a programmable variable gain function that can vary between 0 and 51 This gain is called INAMP input amplifier gain In operation the composite signal is always maximized by the operating software such that the largest possible signal is fed into the next stage of synchronous demodulation this helps optimize the signal noise S N ratio Voltage regulator provides a low noise 5 V DC supply for U44 3 4 2 2 Sync Detector The INAMP stage drives sync detector U32 If the SATINVERT signal is at logic low U32 pin 10 is pulled to ground potential and the stage becomes an inverting amplifier with unity gain When SATINVERT is high the stage becomes a noninverting voltage follower Trimpot R123 is used to equalize the magnitudes of the inverting and noninverting gains 3 4 2 3 Demultiplexer The output of the sync detector drives both halves of U14 U14 demultiplexes the signal synchro nously with the IRGATE and REDGATE steering pulses Low pass filters R47 and C14 R52 and C30 suppress switching transients The signal in each chann
102. siology and the location of the sensor The N 200 measures this time delay and after a few pulse beats calculates the average delay between the occurrence of the R wave and the detection of the optical pulse by the sensor This average delay is used to establish a time window during which the optical pulse is expected at the sensor site A pulse that is received within this time window is considered real pulse and is processed pulse that is received outside the time window is considered an artifact and is rejected Both the average delay and the time window are recalculated with each pulse beat to adjust for changes in the patient s physiology If the ECG signal is irregular or noisy then the optical pulse alone is used to determine pulse rate and initiate saturation calculations Since artifacts often appear indepen dently in the ECG and pulse signals this method provides the most stable measurement of pulse rate and saturation If either the optical pulse or the ECG signal is markedly degraded or lost the appropriate alarm activates and C LOCK ECG synchronization is suspended It will resume once both inputs have been re established 3 1 2 Automatic Calibration Patented automatic calibration mechanisms are incorporated into the N 200 pulse oximetry system U S Patent 4 621 643 and others pending Each sensor is calibrated when it is manu factured the effective mean wavelength of the red LED is determined coded into a ca
103. stments made with the power applied and the cover removed These tests should only be made by qualified ser vice personnel and adequate precaution must be taken against electrical shock WARNING Adjustment procedures described in this section could affect the measurement accuracy of the instrument To insure continued accuracy the procedures must be performed as described using only test equipment specified in this section 4 2 2 Troubleshooting Summary 4 2 2 1 Monitor Symptom 1 INSTRUMENT COMPLETELY IN OPERATIVE AC or battery 2 INSTRUMENT INOPERATIVE BATTERY functional on AC 3 INSTRUMENT FUNCTIONS CORRECTLY ON BATTERY BATT IN USE LIGHT STAYS ON FOR AC NOTE This symptom may turn into Symptom 1 once the battery discharges 4 INSTRUMENT INOPERATIVE RANDOM the STEADY DISPLAY SEGMENTS AND OR CONTINUOUS BEEP Probable Diagnosis A B Blown AC fuse and battery discharged Refer to Section 4 4 1 Blown AC and battery fuses Refer to Sections 4 4 1 and 4 3 5 Failure of the switching circuitry on the charger board Refer to Sections 5 3 4 and 3 7 Power supply failure Refer to Sections 5 3 1 and 3 6 Logic failure on the processor board Refer to Sections 5 4 and 3 4 Failure of battery charger circuit on the charger board Refer to Sections 5 3 3 and 3 7 2 Battery failure Refer to Sections 5 3 and 4 3 5 Blown battery fuse Refer to Section 4 3 5 Blown AC fuse Refer to Sec
104. t a logic high it stops using the ECG R wave as a gating mechanism and lights an LED on the instrument front panel to notify the user that the ECG signal has been lost 3 8 The processor clears the flip flop with CLRLO after a high LEADOFF signal has been recognized NAND gate U10 is provided to latch the flip flop during brief intermittent lead off conditions 3 4 3 4 Power Line Frequency Sensing The mains power AC signal going into the power supply board is transformed to 9 2 VRMS and sensed by one volt crossing comparator U20 The one volt crossing detector produces the logic signal AC which interrupts the processor at the frequency of the AC power line This signal is used to set notch filter U6 to the line frequency automatically adjusting for 60 Hz or 50 Hz power 3 4 4 A D D A Subsection The A D D A subsection is shown on SCHEMATIC PROCESSOR PCB SHEET 4 The A D D A subsection performs both analog to digital and digital to analog conversions A unique feature of the design is the ability to subtract variable DC offsets and post amplify signals prior to A D conversion This allows for accurate measurements of small modulation levels on large DC levels without slow response AC coupling 3 4 4 1 A D Conversion The sequence of a typical A D conversion routine is as follows A 8088 processor selects analog channel for conversion by writing to 8 to 1 analog multiplexer U24 Signals available for conversion are IR
105. te between 2 0 and 3 6 volts Nominal voltage will be 2 8 Note if pins 14 and 28 are accidently shorted during this procedure a temporary Err 6 will result on the first power up after the test Note When the clock calendar assembly containing the lithium battery is replaced a momentary Err 6 message will occur the first time the monitor is subsequently powered up POWERBASE ALIGNMENT The following tests detail the methods to calibrate the zero and span for the analog outputs 1 10 Connect the AC power cord WARNING ELECTRICAL SHOCK HAZARD When the powerbase cover is removed AC power voltages are exposed Do not place fingers or metal tools in contact with AC power sources Place the ON STDBY switch in the ON position Connect the DMM to the SAT output jack J5 on the Middle Daughter PCB schematic rear of the N 200 The jack is a 3 32 phone plug signal to tip and ground to ring Set the SaO 1 dipswitch on the rear of the N 200 to the 0 100 position Set the VOLT 2 dipswitch on the rear of the N 200 to the 0 1 position Press the ZERO button on the rear of the N 200 Examine the DMM for a 0 00 0 01 volts indication If necessary adjust R3 on the Middle Daughter PCB This adjustment is accessible through the hole marked OV in the Upper Daughter PCB Press the FULL button on the rear of the N 200 Examine the DMM for a 1 00 0 01 volts indication If necessary adjust R2 on the Middle Daughter
106. th intermittent noisy or out of spec perform ance of the instrument While these problems may also be related to a component failure they can also be caused in some cases by noise in the environment such as electro cautery or Bovie interference an improperly functioning sensor or misapplication of the sensor by the user If an instrument is suspected of having substandard performance the procedures outlined in Section 5 Testing and Calibration should be followed to help diagnose the problem WARNING The procedures in this section require tests and adjustments made with the power applied and the cover removed These tests should only be made by qualified ser vice personnel and adequate precaution must be taken against electrical shock WARNING Adjustment procedures described in this section could affect the measurement accuracy of the instrument To insure continued accuracy the procedures must be performed as described using only test equipment specified in this section 4 2 2 Troubleshooting Summary 4 2 2 1 Monitor Symptom 1 INSTRUMENT COMPLETELY IN OPERATIVE AC or battery 2 INSTRUMENT INOPERATIVE BATTERY functional on AC 3 INSTRUMENT FUNCTIONS CORRECTLY ON BATTERY BATT IN USE LIGHT STAYS ON FOR AC NOTE This symptom may turn into Symptom 1 once the battery discharges 4 INSTRUMENT INOPERATIVE RANDOM the STEADY DISPLAY SEGMENTS AND OR CONTINUOUS BEEP Probable Diagnosis A
107. the audio alarm by pressing the AUDIO ALARM OFF button again Verify that the AUDIO ALARM OFF indicator goes out and the alarm starts sounding Place ON STDBY switch in the STDBY position and remove all test equipment Powerbase to Monitor Communication AC power must be applied for this test 1 2 Simultaneously press the TREND and EVENT buttons on the rear of the Powerbase Verify that the word appears in the OXYGEN SATURATION display and the word Prt appears in the PULSE RATE display This verifies Powerbase to Monitor Communi cation via the fiber optic link Monitor to Powerbase Communication 1 Locate the eight dip switches on the back of the Powerbase Set switches 3 and 4 DOWN 5 16 position and the rest in the UP position Verify that the FIBER OPTIC PORT labeled DATA on the rear of the Powerbase is not lighted Press the AUDIO ALARM OFF button on the front of the N 200 several times Note that the FIBER OPTIC PORT labeled DATA lights up briefly each time the AUDIO ALARM OFF button is pressed 5 7 10 Middle Daughter PCB Verification 1 2 Connect the DMM to the SAT connector on the rear of the Powerbase Locate the two dip switches on the rear of the Powerbase just above the SERIAL COMM port Set the SaO SCALE switch to the 0 100 position and the VOLT switch to the 0 10 position The DMM must read as follows depending on the indication of the OXYGEN SATURA TION display OXYGEN
108. the bottom cover in the following manner 1 sure that the washers in place under each screw head 2 Before tightening the screws securely check the top cover to see that its front edge mates properly with the front panel Press the top cover down into place if necessary 3 When tightening the screws be careful not to strip the threads in the plastic case by over tightening Recommended screw tightening torque is 16 to 18 in lb 4 4 POWERBASE DISASSEMBLY AND REASSEMBLY Disconnect AC power cord before attempting disassembly Unless otherwise noted the method used for reassembly of the instrument or one of its subassemblies is the reverse of that used for disassembly 4 4 1 AC Fuse Replacement Fuses are contained inside a door above the AC power inlet on the back of the powerbase To gain access unplug the AC cord from the back of the powerbase and open the door by prying the top edge with a small flat blade screwdriver 4 14 Pull out the fuse holder on the right side to gain access to the fuse The holder contains 230 0 5 slo blow fuse Replace the fuse only with the same type and rating Replace the fuse holder by first making sure that the arrow on the holder points to the right and then pressing it into place A removable barrel can be set to either 115 V or 230 V positions If the barrel comes out of its holder be sure that it is replaced so that one of the 115 V settings United States units is
109. tion 4 Refer also to Section 4 for instructions on cover removal and other access procedures Note that certain compo nent level repairs require comprehensive tests of the analog section of the processor PCB to verify correct repair If such repairs are necessary read the appropriate parts of Section 3 that relate to the theory of operation After the repair verify that the circuits perform as described in Section 3 then perform the tests described in this section to verify overall instrument performance WARNING The procedures in this section require tests and adjustments made with the power applied and the cover removed These tests should only be made by qualified service person nel and adequate precautions must be taken against electrical shock WARNING Adjustment procedures described in this section could affect the measurement ac curacy of the instrument To insure continued accuracy the procedures must be performed as described using only test equipment specified in this section It is particularly important that a NELLCOR oximeter pocket tester be available to verify accuracy before adjustment or service is attempted See list of required test equipment Each of the following sub sections is designed to be used independently of the others When any of the sub sections is used by itself it is required that sub section 5 7 be performed to assess overall system operation 5 3 BATTERY CHARGER PCB TESTS 5 4 REGULATED POWER SUPPLY PC
110. tion 4 4 1 AC rectifier failure on the charger board Refer to Sections 5 3 3 and 3 7 AC rectifier filter failure on power supply Refer to Sections 5 3 1 and 3 6 18 V power supplies out of spec Refer to A Failure of microprocessor logic on processor board including the micro processor ROM RAM and associated circuitry Refer to Sections 5 4 and 3 4 5 V power supply out of spec Refer to Sections 5 3 1 and 3 6 Failure of switching circuit on charger board Refer to Sections 5 3 4 and 3 7 10 INSTRUMENT OPERATES DISPLAY SHOWS Err 1 INSTRUMENT OPERATES DISPLAY SHOWS Err 2 INSTRUMENT OPERATES DISPLAY SHOWS Err 3 INSTRUMENT OPERATES DISPLAY SHOWS Err 4 INSTRUMENT OPERATES DISPLAY SHOWS Err 5 INSTRUMENT OPERATES DISPLAY SHOWS Err 6 Probable Diagnosis A Failure of RAM memory on the processor board diagnosed during power up test Refer to Sections 5 4 and 3 4 1 Failure of ROM memory on the processor board diagnosed during power up test Refer to Section 5 4 and 3 4 1 Failure of an LED segment or lamp diagnosed during power up test Refer to Section 3 5 1 4 18 V power supplies out of spec Refer to Sections 5 3 1 and 3 6 Failure of D A conversion circuitry on the processor board Refer to Sections 5 4 6 and 3 4 4 Loss of power without going through normal shut down procedure Refer to Section 3 7 1 Turn ON STDB
111. tion from ON to STDBY through this signal it executes a shutdown procedure The ON mode is activated by bringing the gate of FET switch Q1 high which provides a low ance connection between power supply ground labeled P and signal ground STDBY mode is activated by cutting off Q1 Power supply voltage VPS may be either the battery voltage or the rectified and filtered AC voltage from the powerbase depending on the mode of operation In the following sections the circuit is examined as the ON STDBY switch is moved first from ON to STDBY and then as the instrument is returned to the ON state 3 7 1 1 ON State In the ON state capacitor C2 is discharged The combination of R5 and C2 forms a watchdog timer that ensures processor control over instrument power If C2 is allowed to recharge pin 8 of U1 will go low flip flop U2 will be cleared the gate of Q1 will go low and the connection between power and signal grounds will be broken The processor keeps C2 from recharging by placing a negative pulse on the power supply enable line PSEN at least once every 150 ms The pulse is AC coupled through capacitor C1 its rising edge producing a narrow positive going pulse on U1 pins 1 and 2 The resulting low pulse on U1 pin 3 periodically discharges C2 through diode CR4 Capacitor C1 ensures that only active transi tions on PSEN not static highs or lows have an affect on the watchdog timer The N 200 is thus placed in the STDB
112. to logic high placing positive voltage on the gate of FET switch Q1 Positive gate voltage on Q1 creates a low resistance path between signal ground and power ground As the switched voltage pulse from C5 discharges through R7 U1 6 returns to a logic high and C2 the watchdog timer begins recharging The processor again begins to periodi cally discharge C2 to maintain the instrument in the ON state 3 7 1 5 Voltage Regulator Micropower voltage regulator U3 provides 5 V power to the battery charger PCB Battery charger and ON STDBY sensing circuitry is always on as long as the battery maintains sufficient voltage Total current drain for the circuits on this board is approximately 40 pA 3 7 1 6 Power On Time Delay A time delay provided by CR2 R6 and at the gate of Q1 allows the power supplies to return to ground potential on occasions when the switch is cycled rapidly Without this time delay cycling the switch from ON to STDBY and back to ON might not allow the power supply voltage to fall far enough to generate a reliable power up reset pulse to the processor SCHEMATIC PROCESSOR PCB SHEET 1 power up reset circuit R1 CR1 and C19 3 7 2 Battery Charger Circuit Battery charger circuitry is shown in the upper part of the schematic AC power VCB and VCB 12 5 VRMS is taken from one of the power supply transformer sec ondary windings It is rectified through diode bridge CR6 and filtered by C7 to provide a positive
113. ures or transport The battery is recharged whenever the unit is connected to AC power and is fully recharged in 14 hours Front panel controls allow adjustment of the beeper volume alarm volumes alarm disabling and adjustment of alarm limits for high and low oxygen saturation and high and low pulse rate A con nector is located on the front panel for connection of the patient module assembly The standard patient cable is 4 meters in length and is terminated by a module containing a preampli fier and sensor and ECG connectors The entire patient module assembly is isolated from ground with a maximum leakage current of 10 microamperes This provides safety for the patient from currents generated by faulty equipment e g defibrillators or electrosurgical units WARNING To assure continued patient safety the patient module or sensors must not be replaced with any parts other than those designated or manufactured by Nellcor Incorporated A number of patient safety and labor saving features are incorporated into the N 200 C LOCK ECG synchronization enhances performance in high motion environments such as the ICU or the NICU Three operating modes provide different averaging times adapting the N 200 for use in the presence of varying levels of patient activity The N 200 is equipped with two sets of default alarm limits one for use in monitoring adults and one for neonates e Twelve hours of oxygen saturation and pulse rate
114. wo PCBs as a set by performing the following steps 1 Disconnect all cables on the processor PCB some connectors have retaining clips which must be removed first Cut the tie wrap holding the large electrolytic capacitor on the power supply PCB Disconnect the 2 conductor power cable from the display driver PCB For reassembly verify that the red lead is on top Disconnect the battery leads and switch connector from the battery charger PCB For reassembly verify that the red battery lead connects to the BATT terminal the black bat 4 11 tery lead connects to the BATT terminal and the switch connector is oriented with brown lead on top 5 Remove the power supply PCB and battery charger PCB as one unit The PCBs can now be separated if necessary by disconnecting the 18 conductor flex circuit cable from the battery charger PCB 4 3 3 Front Panel Removal The front panel can be removed after the instrument top cover has been removed Remove the front panel from the top cover by performing the following steps 1 Turn the bottom cover upside down and remove the two Phillips head screws securing the front panel to the bottom cover 2 Disconnect the ON STDBY switch cable from the battery charger PCB For reassembly the switch connector is oriented with the brown lead on top 3 With the bottom cover right side up on the workbench locate the four latches on the front panel that secure the front panel to the
115. y SECTION 5 TESTING AND CALIBRATION 5 1 5 2 5 3 5 4 5 5 5 6 5 7 DESCRIPTION REQUIRED TEST EQUIPMENT BATTERY CHARGER PCB TESTS 5 3 1 Raw DC Voltage 5 3 2 Battery Charging Voltage 5 3 3 Low Battery Instrument Shut Off Voltages 5 3 4 _ON STDBY Switch Test 5 3 5 Battery Operation REGULATED POWER SUPPLY PCB TESTS PROCESSOR PCB TESTS 5 5 1 Processor PCB Voltage Regulation 5 5 2 Calibration Resistor Determination 5 5 3 LED Intensity Control 5 5 4 Input Amplifier INAMP Automatic Gain 5 5 5 Sync Detector Alignment 5 5 6 Channel Gain 5 5 7 RED Channel Gain 5 5 8 Processor 5 5 9 A D D AAlignment 5 5 10 Clock Calendar Lithium Battery Test POWERBASE ALIGNMENT SYSTEM FUNCTION TEST 5 7 1 Operation 5 7 2 Battery Operation 5 7 3 Adult Neonatal Alarm Limits 5 7 4 Pocket Tester Operation 3 15 3 16 3 16 3 16 3 17 3 17 3 17 3 18 4 1 4 6 4 6 4 7 4 7 4 10 4 10 4 10 4 11 4 12 4 13 4 13 4 13 4 13 4 14 4 14 4 15 4 15 4 15 5 1 5 1 5 2 5 2 5 3 5 4 5 5 5 6 5 6 5 7 5 8 5 9 5 9 5 11 5 12 5 12 5 13 5 13 5 14 5 14 5 14 5 7 5 Adjusting Alarm Limits 5 15 5 7 6 Temporary Alarm Silence 5 16 5 7 7 Disabling the Audible Alarm 5 16 5 7 8 Power

service manual nellcor® n-200 pulse oximeter

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service manual nellcor&reg; n-200 pulse oximeter

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service manual nellcor® n-200 pulse oximeter