8481A Manual
Contents
1. Reference HP Part cD Qty Description Mfr Code Manufacturer Part Designation Number Number A2R2 0698 7248 1 RESISTOR 3 16K 1 05W TF TC 0 100 24546 C3 1 8 TO 3161 F A2R3 0698 7224 3 RESISTOR 316K 1 05W TF TC 0 100 24546 C3 1 8 TO 316R F A2R4 0698 7236 7 RESISTOR 1K 1 05W TF TC 0 100 24546 C3 1 8 TO 1001 F A2RT1 0811 3210 1 RESISTOR 31 6 5 05W TF TC 5040 250 14140 1409 1 20 31R6 J A2U1 1813 0060 8 IC MISC TO 8 PKG 28480 1813 0060 A2 MISCELLANEOUS PARTS 0590 1040 1 THREADED INSERT NUT 0 80 06 IN LG SST 28480 0590 1040 5040 6938 6 SPACER 28480 5040 6938 CHASSIS PARTS J1 08481 60024 7 CONNECTOR ASSEMBLY 12 PIN 28480 08481 60024 MP1 08481 40002 9 2 SHELL PLASTIC 28480 08481 40002 MP2 08481 40002 9 SHELL PLASTIC 28480 08481 40002 MP3 08481 20011 8 2 CHASSIS 28480 08481 20011 MP4 08481 20011 8 CHASSIS 28480 08481 20011 MP5 08481 20008 3 1 END BELL 28480 08481 20008 MP6 1460 1978 0 1 SPRING CPRSN 088 IN QD 188 IN OA KG 28480 1460 1978 MP7 1251 3363 8 0 NUT AUOIO CONN 28480 1251 3363 MP8 08481 00002 5 2 SHIELD 28480 08481 00002 MP9 08481 00002 5 SHIELD 28480 08481 00002 MP10 3030 0954 9 SCREW SKT HO CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP11 3030 0954 SCREW SKT HD CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP12 3030 0954 SCREW SKT Ho CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP13 3030 0954 SCREW SKT HD CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP14 3030 0954 SCREW SKT HD CAP 0 80 88 IN LG SST 304 28480 30302. A restored Bulkhead is rebuilt and calibrated at the factory It comes with a calibration report and new calibration sticker for your sensor If you decide to repair the bulkhead yourself you should have an HP 117608 E01 Automated Power Sensor Calibration System and when repairs are finished the appropriate SWR test setup See table 4 for system specifications Note If you repair power sensors often and have the proper calibration systems bulkhead repair can be more economical than replacement A2 Input Amplifier Assembly Printed Circuit If the A2 Input Amplifier Assembly is at fault replace it Replacing the A2 Assembly is usually less costly than the time it takes to troubleshoot and replace faulty components For those who wish to troubleshoot use figure 4 Power Sensor Schematic Diagram Bulkhead Replacement Read repair strategy above Bulkhead replacement differs from repair in that no special tools or skills are required other than those needed to do the FET balance adjustment Procedure 1 Order your new or restored Al Bulkhead Assembly from table 5 Replaceable Parts 2 Follow the disassembly and reassembly procedure for bulkhead removal and replacement located near the end of this manual 3 Check the FET balance using the procedure that precedes the parts list If you did not disturb the wires itis likely that no adjustment will be necessary 4 Place the new calibration sticker on the power sensor cover
3. 10 v TA FOR 8482A ONLY 28480 0180 2781 1 0180 3210 2 1 CAP FXD 47uF 10 v TA FOR 8483A ONLY 04213 11901161 A2C2 0160 0565 2 4 CAP FXD 1000pF 100 v FOR 8481A AND 8482A A2C2 0160 4306 2 1 CAP FXD 100pF 100 V FOR 8483A ONLY 95275 VJO805Y102MF A2C3 0160 0565 2 4 CAP FXD 1000pF 100 V FOR 8481A AND 8482A A2C3 0160 4306 2 1 CAP FXD 100pF 100 V FOR 8483A ONLY 95275 VJO805Y102MF A2C4 0180 0594 9 1 CAP FXD 3 3uF 15 V TA 202L1602 335 M4 A2C5 0160 3094 8 1 CAP FXD 0 1uF 100 V 04222 SR301C104KAAH A2C6 0160 3879 7 1 CAP FXD 0 01uF 100 V 04222 SR201C103MAAH A2C7 0160 0565 2 4 CAP FXD 1000pF 100 V FOR 8481A AND 8482A A2C7 0160 4306 2 1 CAP FXD 100pF 100 V FOR 8483 ONLY 95275 VJ0805Y102MF A2C8 0160 0565 2 4 CAP FXD 1000pF 100 V FOR 8481 AND 8482A A2C8 0160 4306 2 1 CAP FXD 100pF 100 V FOR 8483A ONLY 95275 VJ0805Y102MF A2C9 0180 2515 8 1 CAP FXD 47uF 6 V TA 202L6301 476 M7 552 A2C10 0180 2545 4 1 CAP FXD 100uF 4 V TA 202L6301 107 M6 S52 A201 1854 0610 0 1 TRANSISTOR NPN SI TO 46 FT 800MHZ 04713 A2R1 0698 3260 9 1 RESISTOR 464K 4 196 125W TF TC 0 100 FOR 8481A ONLY 28480 0698 3260 A2RI 0757 0483 8 1 RESISTOR 562K 4 196 125W TF TC2O 100 FOR 8482A 28480 0757 0483 ONLY A2R1 0698 8352 9 1 RESISTOR 787K 1 125W TF TC 0 100 FOR 8483A ONLY 28480 0698 8352 12 Table 5 Replacement Parts 2 of 2
4. Bulkhead Repair Read the repair strategy above Before beginning repair inspect the center conductor and outer conductor with a magnifying glass If you have any burrs or scratches visible on the connecting surfaces you should complete the entire procedure below or replace the bulkhead If your connecting surfaces are acceptable repair your bulkhead by replacing cartridge A1MP16 starting with step 9 Do not attempt repair without the following equipment Equipment Power Sensor Calibration System HP 117608 E01 Type N Connector Gage 85054 60024 Precision 7mm Connector Gage for Option 001 1250 1875 SWR Test Set See table 4 for specifications Rebuilding the Bulkhead 1 Refer to the parts list and figures 6 7 and 8 Order the internal type N bulkhead parts 1 through A1MPI2 HP 8482 and 8483 do not use AIMPI2 polyiron slug The precision 7mm connector 131 1 comes assembled so 1 2 and MP3 are unnecessary 2 Setup the necessary equipment for your SWR test See table 4 in this manual for system specifications 3 Remove the bulkhead assembly from the Power Sensor See the disassembly procedure near the end of this manual 4 Using a 5 8 in 16mm wrench remove the cap nut and disassemble the bulkhead Save the cap nut 11 and polyiron slug AIMP12 Discard the old parts 5 Build the RF Connector Assembly AIMPI MP2 and MP3 If you have an HP 8481 Option 001 ignore this step a S
5. apart Remove the shells and magnetic shields 3 Position the Power Sensor as shown in figure 8 top The small hole 5 should be on the left side of the RF input connector Remove the allen cap screws 1 2 10 and 13 Loosen 11 and 12 Remove the upper chassis from the Power Sensor 4 Remove the spring clamp cap screw 7 to free the gold leads which come from the Bulkhead Assembly 5 Remove cap screws 3 4 and 5 6 Slide the Bulkhead Assembly straight out from the chassis 7 Remove cap screws 8 9 11 12 14 and 15 7 Lift the A2 Input Amplifier and J1 connector out of the chassis 24 Figure 10 Power Sensor Hardware Locations Reassembly Procedures Caution The gold wires connecting the Al Bulkhead Assembly and the A2 Input Amplifier Assembly are extremely delicate and may be easily broken Be careful when working around them 1 Set the printed circuit board and connector into place as shown in figure 10 bottom view 2 Insert cap screws 8 9 11 12 14 and 15 but do not tighten 3 Center the circuit board so there is equal air gap between each side and the chassis Tighten 8 9 14 and 15 4 With small hole 5 to the left carefully insert the gold leads on A1 bulkhead assembly through the holes in the black plastic guide on A2 input amplifier 5 Insert screw 3 4 and 5 Tighten only screw 5 25 6 Using tweezers position the ends of the gold wires over the electrical pads Caution DO NOT tighten cl
6. assembly is applied to the two field effect transistors FETs in A2U1 These transistors function as a sampling gate or chopper The sampling rate is controlled by a 220 Hz square wave supplied by the power meter The amplitude of the sampling gate output at pin 3 of A2UI is a 220 Hz square wave proportional to the power input The sampled 220 Hz ac output is applied to the input amplifier A2Q1 which is the input stage for an operational amplifier figure 5 The ac gain of the operational amplifier is approximately 700 A dc feedback voltage from the power meter Auto Zero circuit is coupled to the input of FET A2UIQI to set the zero level The voltage is developed across the voltage divider consisting of A2RI and the series resistance of the thermocouple A1TCI When the Power Sensor is used with an HP Power Meter the short to ground at J1 K Mount Resistor causes the power meter to automatically select the proper measurement range of 30 to 20 dBm With the HP 435 series Power Meter this short serves no function POWER SENSOR CABLE l V POKER SENSOR emm e POWER METER e SAMPLED AC INPUT 228 H x Figure 5 Operational Amplifier Troubleshooting The troubleshooting information is intended to first isolate the Power Sensor or power meter as the defective component When the Power Sensor is isolated troubleshooting information is intended to identify A1 Bulkhead Assembly or A2 Input Amplifier Assembly as the defective compon
7. operation troubleshooting and repairs Test equipment which meets or exceeds the critical specifications in table 3 may be used in place of the recommended instruments for troubleshooting the Power Sensor NOTE Check your warranty Opening the Power Sensor will void warranty Principles of Operation For the following discussion refer to figure 4 Schematic Diagram and figure 5 Operational Amplifier The operational amplifier is made up of the Power Sensor input amplifier A2QI and the first amplifier stage in the power meter For additional information on thermocouple sensors refer to HP Application Note 64 1 Fundamentals of RF and Microwave Power Measurements The Al Bulkhead Assembly provides a 50 ohm load HP 8481 and 8482A or a 75 ohm load HP 8483A to the RF signal applied at the RF INPUT The rf signal is coupled through a de blocking capacitor and absorbed by the thermocouples which generate a dc voltage proportional to the rf input power The dc voltage is routed from the thermocouples to the input amplifier on gold wires to reduce undesired thermocouple effects The gold wires pass through ferrite beads A2EI and A2E2 which are located in the black plastic block See figure 2 The ferrite beads increase the self inductance of the gold wires causing this portion of the wires to provide the properties of an rf choke The result is to minimize rf feed through to the A2 Input Amplifier Assembly The dc output from the bulkhead
8. 9054 MP15 3030 0954 SCREW SKT HD CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP16 3030 0954 SCREW SKT HD CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP17 3030 0954 SCREW SKT HD CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP18 3030 0954 SCREW SKT HO CAP 0 80 88 IN LG SST 304 28480 3030 9054 MP19 3030 0422 8 4 SCREW SKT HD CAP 0 80 88 IN LG SST 302 00000 ORDER BY DESCRIPTION MP20 3030 0422 8 SCREY SKT HD CAP 0 80 188 IN LG SST 302 00000 ORDER BY USED TO MOUNT THE PRINTED CIRCUIT BOARD DESCRIPTION MP21 3030 0422 8 SCREW SKT HD CAP 0 80 88 IN LG SST 302 00000 ORDER BY USED TO MOUNT THE PRINTED CIRCUIT BOARD DESCRIPTION MP22 3030 0422 8 SCREW SKT HD CAP 0 80 88 IN LG SST 302 00000 ORDER BY USED TO MOUNT THE PRINTED CIRCUIT BOARD DESCRIPTION MP23 3030 0436 4 SCREW SKT HD CAP 0 80 5 IN LG SST 300 00000 ORDER BY DESCRIPTION MP24 5040 6939 7 CLAMP 28480 5040 6939 MP25 5040 6940 0 BLOCK 28480 5040 6940 MP26 1250 0597 2 ADAPTER COAX STR M N F N MP27 08481 80002 3 8481A ID LABEL 28480 08481 80002 MP28 08482 80002 4 8482A ID LABEL 28480 08482 80002 MP29 08483 80001 6 8483A ID LABEL 28480 08483 80001 MP30 08486 80001 E CAL LABEL BLANK 28480 08486 80001 MP31 08481 80005 6 MYLAR TAPE COVERS CAL LABEL 28480 08481 80005 MP32 08486 80005 1 INFO LABEL SIDE 26480 08486 80005 MP33 7120 2422 7 WARNING LABEL SIDE 26480 7120 2422 13 Blank Skipped List of Manufacturers Service Service instructions consist of principles of
9. LON OA NOI 7 Ux 206 0 9 2 i T OY 1 4 3 3 SMOTIO 3 0 ONY H o ox 2 Na efor st 13 S1H3ND WO2 40 5301 HI E no a o oj 50 301711 NI 7 72 ooo INO 5WHO NI ONY LS 5 38 mya 303121081 IS MIRO M3IA MIS in SION tr d BAT VL Mudo anyo 40 OLOM IHY f wO a CP woan 1 EY AXAN mena Vd ALLVAR OY LN r ipe LLO LON LY PORE 20 rar 0 090 4 5 E E dayn w 018 9 4 HOLS x HOw 5 NOI 15000 f Wan LOY g NAVI HOSNIS 13404 vani WIN R04 OL TH OFZ 20 2 3v anewvs amaa uvg HR 0009 Ered VERVE 0009 2800 ZIYON 0009 07090 LEY AE IS SY 0 2013170 ASSY QU In 2090 VERY ICOON 10O VERO 790215 0212118 INANI ZY J am v amp VOIT VAR VTE S BONS HMDA 003 7 7 Di Nem 5 1400200 0 oe Mame I 11 Figure 4 Schematic Diagram Table 5 Replacement Parts 1 of 2 Refer
10. Portions of Operating and Service Manual HP 8481A HP 8482A HP 8483A Power Sensor 1975 1990 Manual was scanned and converted to text formatting The content is the same as the original manual but formatting is slightly different Manual Part No 08481 90049 Replaceable Parts Table 5 is a list of replaceable parts Figure 2 illustrates the major parts To order a part listed in the Replaceable Parts table quote the Hewlett Packard part number with Check Digit CD indicate the quantity required and address the order to the nearest Hewlett Packard office Note Within the USA it is better to order directly from the HP Parts Center in Roseville California Ask your nearest HP office for information and forms for the Direct Mail Order System Also your nearest HP office can supply toll free telephone numbers for ordering parts and supplies MP 11 22 NOT SHOWN SAME AS MP10 Figure 2 illustrated Parts Breakdown A2 INPUT AMPLIFIER ASSEMBLY BOTTOM Vv 42 INPUT AMPLIFIE AL BULKHEAD ASSEMBLY Figure 3 Component and Assembly Locations 10 101700 JHI NI 1 8103111 5 8 O1 yle 4 Y 111 1 35 LON 138 9 355 1 341 30 31090 P 310 181 8 3 01312 JON 5 911355 0 3 1111113 53715 733 HL 0130 A TINNY IA AWW SIMI IC 30 5717 147078 Nid HL 01 4 C ov 1 31 531190 0 391 THOS
11. amp screw 6 excessively or the FET circuit may be broken 7 Place and hold plastic clamp 16 over the gold wires As you tighten the clamp screw watch the compression spring Tighten the clamp screw 7 only until the spring coils touch Any further tightening could damage the FET circuit 8 Place the upper chassis in position and insert cap screws 1 2 10 and 13 9 Tighten 1 2 3 and 4 10 Tighten 10 11 12 and 13 11 Place the plastic shells magnetic shields and the chassis together as shown in figure 1 Snap the plastic shells together 26
12. e used to clean connectors 22 Caution The RF connector bead deteriorates when contacted by any chlorinated or aromatic hydrocarbon such as acetone trichlorethane carbon tetrachloride and benzene Do not attempt to clean connectors with anything metallic such as pins or paper clips Clean the connector face by first using a blast of compressed air If the compressed air fails to remove contaminants use a cotton swab dipped in isopropyl or ethyl alcohol If the swab is too big use a round wooden toothpick wrapped in a lint free cloth dipped in isopropyl or ethyl alcohol Figure 9 Removing the Power Sensor s Cover 23 Disassembly Procedure Disassemble the Power Sensor by performing the following steps Caution Disassembly must be performed in sequence described below otherwise damage may be caused to the two gold wires between the bulkhead assembly and the input amplifier assembly If these wires are damaged the Al Bulkhead Assembly must be repaired or returned to the factory for repair Note Every Power Sensor has an individually prepared graph on the housing If more than one power sensor is disassembled at a time be sure to mate the correct Power Sensor and housing when reassembling 1 Insert the blade of a large screwdriver between the two piece plastic shell at the rear of the Power Sensor Gently pry the sections apart See figure 9 2 Proceed to the other side of the connector and again pry the cover sections
13. ence HP Part Number cD Qty Description Mfr Code Manufacturer Part Number Designation Al 08481 60004 3 1 BULKHEAD TYPE N FOR 8481A ONLY 28480 08481 60004 A1 08481 60005 4 1 BULKHEAD APC 7 FOR 8481A OPT 001 ONLY 28480 08481 60005 A1 08482 60003 3 1 BULKHEAD TYPE N FOR 8482A ONLY 28480 08482 60003 A1 08483 60003 4 1 BULKHEAD TYPE N FOR 8483A ONLY 28480 08483 60003 A1MP1 1250 0818 0 1 NUT CONN RF A1MP1 1250 1466 6 1 7MM RF CONNECTION ASSY OPT 001 ONLY A1MP2 1250 0016 0 1 RING RF CONN A1MP3 1250 0916 9 1 BODY RF CONN A1MP4 1250 0917 0 1 CONNECTOR RF CONTACT A1MP4 1250 0816 8 1 7MM CONTACT OPT 001 ONLY A1MPS 1460 0977 7 1 SPRING COMPR A1MP6 5020 3296 1 1 CENTER CONDUCTOR A1MP7 5020 3297 2 1 SLIDING CONTACT A1MP8 5040 0306 0 1 INSULATOR A1MP9 0470 0013 2 1 SEALANT THD RED A1MP10 08481 20015 2 1 BULKHEAD A1MP11 08481 20016 3 1 CAP NUT A1MP12 08481 40006 3 1 POLY IRON SLUG 8481A ONLY A1MP13 08481 60009 8 1 CARTRIDGE ASSY 8481A ONLY A1MP13 08482 60004 4 1 CARTRIDGE ASSY 8482A ONLY A1MP13 08483 60006 7 1 CARTRIDGE ASSY 8483A ONLY 2191 0831 0 1 010 WASHER FLAT A2 08481 60025 8 1 BD AY PWR SENSOR FOR 84814 28480 08481 60025 A2 08482 60013 5 1 BD AY PWR SENSOR FOR 8482A 28480 08481 60013 A2 08483 60007 8 1 BD AY PWR SENSOR FOR 84834 28480 08481 60007 A2 0590 1040 1 1 THREADED INSERT NUT 0 80 06 IN LG SST 46384 YC3 1S05 1 0180 2515 8 1 CAP FXD 47uF 6 V TA FOR 8481A ONLY 28480 0180 2515 A2C1 0180 2781 0 1 CAP FXD 39uF
14. ent Before you open the Power Sensor to continue with the troubleshooting procedures try the substitution method of elimination Use another Hewlett Packard power meter known to be in good operating condition with the suspected power sensor and cable If the same problem occurs with the known good power meter substitute a known good power sensor cable Troubleshooting should be performed with the Power Sensor opened the printed circuit board exposed See Disassembly close to the end of this manual When a failed assembly has been identified go to Repair directly following Troubleshooting Caution Excessive power will damage the thermocouples Power Meter To ensure the power meter is providing the correct 220 Hz signal check the following levels of the square wave with an oscilloscope e At the white black Wire 0 05 0 05 Vdc top of square wave e At the white brown wire 9 0 Vdc bottom of square wave If the levels are correct the Power Sensor is at fault Continue troubleshooting Al Bulkhead Assembly If the levels are incorrect the power meter is at fault Refer to the power meter service manual for troubleshooting information Power Sensor The most common cause of Power Sensor failure is the application of power levels beyond the specified tolerance The second most common cause of failure is applying torque to the body of the Power Sensor Either of these common causes will damage the bulkhead cartridge
15. lip the C ring into the groove on the RF connector body A1 MP3 b Place the nut face down knurled end up on a flat surface c While squeezing the C ring with long nose pliers slide the connector body into the nut until the ring snaps into place Figure 6 P O A1 Bulkhead Assembly 6 Build the Center Pin Assembly AIMPA 5 6 7 8 and 9 a Insert the threaded end of center contact AIMPA through the insulator AIMP8 b Place a very small amount use the point of a wooden toothpick of red anaerobic sealant A1 MP9 on the threads of AIMP4 Be careful not to get any sealant near the insulator c Use your fingers to screw the center contact Al MP4 into the center conductor Al MP6 until tight The round insulator should be squeezed tight enough so that it will not rotate Do not scratch or burr the two shafts d Place the spring into AIMP6 e Patiently place the sliding contact snowflake A1MP7 so that the snowflake fingers without being damaged surround the spring and press against the inner surface of center conductor The snowflake should spring back when pressed Lud n 030 MIN PROTRUSION Figure 7 A1 Bulkhead Center Contact Assembly 7 Screw the bulkhead into the center pin assembly as shown in figure 8 Tighten in place to 50 5 in Ibs 565 N cm 8 Usethe appropriate gage to verify pin depth When pin depth is correct go to next step Cartridge Replacement Cartridge Re
16. placement If you do not need to replace the inner and outer conductors of your bulkhead start here The procedure assumes the bulkhead assembly is removed from the Power Sensor 9 Order one cartridge replacement AIMP13 from the replaceable parts list 20 10 Place the bulkhead on its face connector side down with the gold wires pointing up Using a 5 8 in 16 mm open end wrench remove the cap nut AIMP11 11 Turn the bulkhead assembly upside down and shake out the old parts Watch where the polyiron slug 1 12 rolls to and keep it for the new cartridge unit MP1 MP3 Figure 8 1 Bulkhead Illustrated Parts Breakdown Caution The gold wires on the new cartridge unit are easily damaged and cannot be repaired 12 Slip washer AIMPI4 inside the bulkhead A1MP10 Now load in the new cartridge unit with the gold wires pointing out holding the polyiron slug inside the unit until everything is in place 13 Press the top of the bulkhead A slight spring like action indicates the cartridge is properly seated If the cartridge unit does not spring a little when pressed carefully remove the cartridge unit so you do not damage the gold wires and use a thinner washer AIMPI5 If it still does not spring you should rebuild the center conductor step 6 with new parts 21 Caution Damage can occur to both the cartridge and center conductor if they are not properly mated If no springlike action or give is present remove
17. the cartridge assembly and rebuild the center conductor with new parts 14 15 16 17 18 Tighten the cap nut to finger tight then torque the cap nut to 35 5 in Ibs 395 N cm Reassemble the power sensor using the reassembly procedure at the end of this manual Test for SWR Check the FET balance using the procedure prior to Replaceable Parts If you were careful not to disturb the wires above the PC board A2 this step may not be necessary Calibrate the Sensor using your HP 117605 E01 Automated Power Sensor Calibration System Place the new sticker on the Power Sensor cover A2 Assembly Replacement and Soldering To replace the A2 printed circuit assembly you will have to perform some soldering to remove and replace the wires from Connector J1 Remember the Power Sensor is a highly sensitive device As such it is affected by very small temperature differences between its components After doing any soldering in the unit wait several hours for the unit to reach thermal equilibrium before using or testing it 1 2 3 Use a temperature controlled 600 F 311 C with a zero crossover tip Use a low temperature RMA flux SN 62 solder Do not attempt to remove flux residue from around solder joints We have found that using a cleaning solution spreads the flux in a thin sticky layer over the entire assembly Connector Cleaning Keeping in mind its flammable nature a solution of pure isopropyl or ethyl alcohol can b
18. unit which holds the thermocouples If this happens the fault will cause a short or an open between the two gold wires Caution Be extremely careful when measuring across the gold wires They are delicate and can be damaged easily 1 Disconnect all cables from the power sensor 2 Remove the clamp holding the two gold wires 3 Resistance measured between the two gold wires from the Al Bulkhead Assembly should be 200 10 ohms HP 8481A 245 12 5 ohms HP 8482A or 375 17 5 ohms HP 8483A If you cannot obtain the proper resistance failure is usually indicated by an open circuit the Al Bulkhead Assembly is defective If the resistance is correct continue to A2 Input Amplifier A2 Input Amplifier Assembly It is extremely rare for the A2 Assembly to fail Eliminate the power meter the bulkhead assembly and the connectors before suspecting the A2 Assembly In most cases the operational amplifier made up of A2Q1 and the first amplifier of the power meter figure 5 is operating correctly if the dc voltage on the metal cover of 201 collector is 70 30 mV dc Refer to the schematic to troubleshoot further Repair Power Sensor repair consists of Al Bulkhead replacement or repair and A2 Input Amplifier replacement Repair Strategy Bulkhead You can choose to either replace your A1 Bulkhead Assembly or repair it yourself We recommend replacing the A1 Bulkhead with a new or restored bulkhead over attempting to rebuild it
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