SERVICE MANUAL MODEL 1540/1541 DISK DRIVE
Contents
1. 4 Inch floppy disk Single sided single density soft sectored double density can be used but not needed Commodore serial interface Second serial port for chaining a second drive or printer MOS 6502 microprocessor I MHz clock 2K RAM 16K ROM 400 Bytes sec Program sequential relative random access and user Up to 144 different files per diskette C64 VIC 20 SX64 Educator 64 Plus 4 C16 2031 4040 C1551 C1571 120 Volts AC 60Hz integral power supply with external I Amp fuse 30 Watts maximum SPINOLE RW HEAD piney MOTOR SPINDLE MOTOR SPEED CONTROL PROTECT SENSOR SPINDLE STEPPER READ DRIVE ORIVE write INT CIRCUITS CIRCUITS CIRCUITS ATN CLK DATA ACTIVITY LED POWER ON LED CARE AND MAINTENANCE DO NOT use MAGNETIZED tools when repairing or adjusting a disk drive DO NOT place a disk drive near any device which generates noise e g motors radios televisions DO NOT stack drives upon each other or in any way inhibit air flow around the unit HEAT BUILD UP can cause disk failures Periodically CLEAN the read write head with 90 isopropyl alcohol and a cotton swab CHECK load pad for excess wear Clean or replace as necessary Take the following precautions when handling a diskette ALWAYS store a diskette in its jacket Use ONLY felt tip pens when writing on the label of a diskette Do not bend or physically damage a diskette Do not place a disk2. PCB ALPS MOTOR CONTROL BOARD SCHEMATIC 5 12Y O MOTOR OUT RED QUT BLU RS 1 a2 i 2517 O MOTOR 8 R4 22 6 LAI 7 810 vai N 85 CAS R7 SYMBOL DESCRIPTION LC Ql Q2 Q3 Q4 Sony CX 065B Transistor 28C2785 Transistor 28C2785 Transistor 28A1175 Transistor B703 Q36E CR 1 2 3 4 5 Diode IN4148 R1 7 R2 R3 R4 R5 R6 R8 R9 R10 VRI C1 5 6 C2 C3 C4 9 C7 C8 Resistor 1 kOhm 1 4W Resistor 68 kOhm 1 4W Resistor 220 Ohm 1 4W Resistor 3 3 kOhm 1 4W Resistor 2 7 kOhm 1 4W Resistor 820 Ohm 1 4W Resistor 150 Ohm 1 4W Resistor 0 68 Ohm 2W Resistor 5 1 kOhm 1 8W Variable Resistor 20 kOhm Capacitor Electrolytic 10uF 35V Capacitor 0 0047uF 50V Capacitor 0 033 50V Capacitor Tantalium 0 47uF 35V Capacitor Tantalium 2 2uF 16V Capacitor 0 068uF 50V
3. is a 2048 x 8 bit RAM UB2 resides at memory locations 0000 07FF This memory is used for processor stack operations general processor housekeeping use program storage and 4 temporary buffer areas UCS UC6 and UC7 decode the addresses output from the processor when selecting RAM 1541 CIRCUIT THEORY Tua kii itti Cte gt we SESIA SEC 4 m 3 NEZ m er z w Za The Serial Interface UC3 is a 6522 Versatile Interface Adapter VIA Two parallel ports handshake control programmable timers and interrupt control are standard features of the VIA Port B signals PB0 PB7 control the serial interface driver ICs UB1 and UA1 CLK and DATA signals are bidirectional signals connected to pins 4 and 5 of P2 and P3 ANT Attention is an input on pin 3 of P2 and P3 that is sensed at PB7 and CAI of UC3 after being inverted by UAI ATNA Attention Acknowledge is an output from PB4 of UC3 which is sensed on the data line pin 5 of P2 and P4 after being exclusively ored by UD3 and inverted by UBI is selected by UC7 pin 7 going low when the proper address is output from the processor resides at memory locations 1C00 1COF 1541 CIRCUIT THEORY EGR EE PSS Microprocessor R W and Motor Control Logic UC2 is a VIA also During a write operation the microprocessor passes the data to be recorded to Port A of UC2 The data is then loaded into the PLA para
4. 41 CIRCUIT THEORY The Clock Circuits Crystal Y1 outputs a 16Mhz clock signal THis is input to UDS on pin 8 UDS is configured as a 16 frequency divider The output of UDS pin 12 is a I MHz clock signal used as the system clock Phase 0 for the microprocessor UE6 is a programmable counter 16 15 14 13 that outputs a varying frequency clock used to compensate for the difference in recording area sector for sectors on inner tracks Trks 1 2 3 as compared to sectors on out most tracks Trks 33 34 35 The area sector for inner tracks is less than the area sector for out most tracks so the recording clock frequency is increased when writing on inner tracks to keep the flux density constant This clock output is on pin 12 of UE6 Tracks Clock Frequency Divide By 1 17 1 2307 MHz 13 18 24 1 1428 MHz 14 15 30 1 0666 MHz 15 31 35 1 MHz 16 1541 CIRCUIT THEORY I pes 11212 1 28 22 evoe 8 0 utd 4 bi zr 28 12 de Sot wt LF A ro ay to 4 Microprocessor Control of RAM and ROM UB3 and UB4 are 8192 x 8 bit ROMS that store the Disk Operating System DOS UB3 resides at memory locations C000 DFFF UB4 resides at memory locations E000 FFFF UCS and UC6 decodes the addresses output from the microprocessor when selecting these ROMS UB2
5. 7 857 2200 58 2 02 CUT TRACE 3 INSTALL JUMPER WIRES BETWEEN UAI pin 8 and UBI pin 5 UAI pin 9 and Anode UBI pin 6 and UD3 pin 5 on BACK of board 4 CUT circuit trace between CR7 Anode and UD3 pin 5 on BACK of board PCB ASSEMBLY 250442 46 BOARD LAYOUT i 1 2 ae aun 7 E 3 EE ue 8 allt mE ay T ila ET is T En 3 SLIRSTITLITE HESTEINK pr m 1 ala UMOUS SI ZppOSZ 824 8 8 Jagwnu 35 Ajquiasse 10 suaquinu Ajquussse OM 20 pasn aq ued 5424 neways 947 krol 310N DILVW3HIS t E Ts b ii hii lt wi OVET 85 gt dd e n E lid Siami SA 22 1021 8 2 KF Se TA 4 97 kad g 5 N 12 7 144 55 san re led 3 SI 9r 541 LHOHS SOINOHIM3N 8StZLLSC DILVW3HIS 1540 1541 POWER SUPPLY ASSEMBLY PARTS LIST FUSE HOLDER 903614 01 ROCKER SWITCH 904509 01 POWER CNNCT FILTER 903467 03 sub 325552 01 FUSE SLOW BLO 250V 1 0A 903556 16 POWER TRANSFORMER 1540009 02 POWER SUPPLY 1540002 2 POWER SUPPLY 1540002 SHIELD WIRE GREEN YELLOW 5 BLUE E 3 BLACK E 6 BLUE 4 ORANGE INPUT VOLT 10 INPUT VOLT 410 7 ORANGE PRIMARY SECONDARY TRANSFORMER TOP ah 27 HARNESS ASSEMBLY DRAWING PA
6. A Programmable Logic Array on the short boards Read Write Control Logic During a write operation UD3 converts parallel data into serial data The output on pin 9 is input to NAND gate UFS pin 4 UFS outputs the serial data on pin 6 at the clock rate determined by input signal on pin 5 The output clocks the D flip flop UF6 The outputs of UF6 and drive the write amplifiers During a read operation data from the read amplifiers is applied to the CLR input of counter UF4 The outputs C and D are shaped by the gate UES UES outputs the serial data on pin 1 then it is converted to parallel data by UD2 The output of UD2 is latched by UC3 The serial bits are counted by UE4 when 8 bits have been counted UF3 pin 12 goes low UC1 pin 10 goes high and UF3 pin 8 goes low indicating a byte is ready to be read by the processor UC2 monitors the parallel output of UD2 when all 8 bits are 1 the output pin 9 goes low indicating a sync bit has been read 1541 CIRCUIT THEORY Read Amplifier Circuits When data is recorded on the disk a 1 bit is represented on the disk by a change in direction of magnetic flux caused by a change in direction of current passed through the R W coil in the R W head When a 0 bit is to be recorded no change in current flow direction occurs causing the direction of the magnetic flux to remain the same on the disk RAN HEAD RW 1 RW 20 When data is being read from the
7. ND MOTOR CONTROL LOGIC o READ WRITE CONTROL LOGIC READ AMPLIFIER o WRITE AMPLIFIER o POWER UP DOWN WRITE PROTECTION o STEPPER MOTOR CONTROL CIRCUITS o SPINDLE MOTOR CONTROL CIRCUITS e TROUBLESHOOTING GUIDE e RESISTANCE CHECKS e CASEWORK ACCESSORY PARTS LIST e MODEL INDENTIFICATION e DEVICE NUMBER CHANGE e PC ASSEMBLY 1540001 o BOARD LAYOUT o PARTS LIST o PIN CONFIGURATIONS o SCHEMATIC e PC ASSEMBLY 1540048 o BOARD LAYOUT o PARTS LIST o UPGRADE NOTES o SCHEMATIC e PC ASSEMBLY 250442 250446 o BOARD LAYOUT o PARTS LIST o IC PINOUTS AND INTERNAL DIAGRAMS o SCHEMATIC e POWER SUPPLY ASSEMBLY 154002 o PARTS LIST o TRANSFORMER o ASSEMBLY DRAWING e ALPS DRIVE ASSEMBLY o PARTS LIST o WIRING DIAGRAM AND LAYOUT o MOTOR CONTROL PCB SCHEMATIC e NEWTRONICS DRIVE ASSEMBLY o PARTS LIST o WIRING DIAGRAM AND LAYOUT o MOTOR CONTROL PCB SCHEMATIC GENERAL DESCRIPTION MAXIMUM STORAGE MEDIA INPUT OUTPUT CONTROLLER MEMORY DATA TRANSFER RATE FILE TYPES NUMBER OF FILES COMPUTERS MEDIA COMPATIBILITY POWER REQUIREMENTS POWER CONSUMPTION C1541 DISK DRIVE PRODUCT SPECIFICATION The C1541 Disk Drive is an external 5 1 4 inch floppy diskette recorder offering high speed and capacity for programs and data It is an intelligent device containing its own microprocessor RAM ROM and operating systems software for faster speed of throughput and memory efficiency in the computer 170K of data formatted 35 tracks 5 1
8. RTS LIST 32551901 Alps Drive Black 32551902 Alps Drive Brown 1 31410001 ALP DOOR HUB ASSEMBLY 1 Door Assy w Spring 2 Hub Collet Assy 3 Arm Support Assy 2 41310101 ALP LEFT DISK GUIDE ASSEMBLY 1 Diskette guide 2 LED Assy w Harness 3 Write Protect Assy 3 31410201 ALP RIGHT DISK GUIDE 4 31410301 ALP FRONT BEZEL Black 31410302 ALP FRONT BEZEL Brown 5 31410401 ALP R W HEAD ASSEMBLY 1 R W Head 2 Load Arm w Pad 3 Metal Band 31410501 ALP STEPPER MOTOR ASSEMBLY 4 Stepper Motor w Harness 5 Stepper Motor Pulley 6 31410601 ALP D C MOTOR 7 31410701 ALP MOTOR CONTROL PCB ASSEMBLY 1 Motor Control PCB 2 Harness Array 8 31410801 ALP TENSION PULLEY ASSEMBLY 1 Pulley Wheel w Spring 2 Plastic Housing 9 31410901 ALP HOUSING SPINDLE ASSEMBLY 1 Housing Base 2 Spindle Assy 3 L R Guide Shafts 31411001 ALP DRIVE BELT 10 31411101 ALP EJECT ASSEMBLY 1 Eject Plate 2 Eject Spring 31411201 ALP HARDWARE 3 Assorted Screws 4 Zero Stop Tab 3147401 UNV Replacement Load Pad ALPS DRIVE ASSEMBLIES 1540 1541 E R W Erase 43 xen RED YEL RED i MOTOR CONTROL P C B SS READ WRITE HEAD ASSEMBLY YE Bra MOTOR ON G O ME RETUR BLU MOTOR RETI 9 Exc GAY TACH Sree VEL 5 TAGH DC MOTOR RED MOTOR CONTROL PCB FUNCTION STEP MOTOR 200 gacgacaa aoaccaao c J4 12 BAN MOTOR ON ORG RETURN BLK gt DC MOTOR CONTROL
9. SERVICE MANUAL MODEL 1540 1541 DISK DRIVE NOVEMBER 1985 PN 314002 01 Commodore Business Machines Inc 1200 Wilson Drive West Chester Pennsylvania 19380 U S A Commodore makes no expressed or implied warranties with regard to the information contained herein The information is made available solely on as is basis and the entire risk as to quality and accuracy is within the user Commodore shall not be liable for any consequential or incidental damages in connection with the use of the information contained herein The listing of any available replacement part herein does not constitute in any case a recommendation warranty guaranty as to quality or suitability of such replacement Reproduction or use without expressed permission of editorial or pictorial content in any matter is prohibited This manual contains copyrighted and proprietary information No part of this publication may be reproduced stored in a retrieval system or transmitted in any form by any means electronic mechanical photocopying recording or otherwise without the prior written permission of Commodore Electronics Limited Copyright 1985 by Commodore Electronics Limited All rights reserved CONTENTS e SPECIFICATIONS e BLOCK DIAGRAM e CARE AND MAINTENANCE e OVERVIEW e FLASH CODE e CIRCUIT THEORY o POWER SUPPLY o RESET LOGIC o CLOCK CIRCUITS o MICROPROCESSOR CONTROL OF RAM AND ROM o SERIAL INTERFACE o MICROPROCESSOR R W A
10. ap 16 3 ohms Erase coil end to end CASEWORK ACCESSORY PARTS LIST 1540 1541 TOP CASE IVORY C 1540014 01 1540 41 BOTTOM CASE IVORY C 1540015 00 1541 TOP CASE BROWN C 1540014 03 1541 BOTTOM CASE IVORY 1540015 03 SHIELD COVER 1540013 03 LED ASSEMBLY C 1540013 SELF ADHESIVE FOOT C 950150 02 1540 NAMEPLATE C 1540016 02 1541 NAMEPLATE C 1540052 00 POWER CORD ASSEMBLY C 903508 04 6 PIN DIN CABLE C 1515001 01 USER S MANUAL C 1540031 03 DEMO DISKETTE C 1540024 01 NOTE All 1540 Disk Drives were manufactured prior to any changes to the board and used the Alps drive exclusively 1541 MODEL IDENTIFICATION PCB Assy s 1540008 01 Schematic 1540001 e Original Long Board e Has4 discreet 2114 RAMs e ALPS Drive only PCD AS 1940048 Schematic 1540049 e Referred to as the CR board e Changed to 2048 x 8 bit RAM pkg e A40pin Gate Array is used e Alps Drive 01 e Newtronics Drive 03 PCB Assy 250442 01 Schematic 251748 Termed the 1541 A e Just one jumper change to accommodate both types of drive Schematic 251748 See Notes Termed the 1541 2 e Just one jumper change to accommodate both types of drive NOTE The simplest way to identify which drive you have is by door assembly Alps is made with a push down door and Newtronics has a flipper type door DEVICE NUMBER CHANGE The 1540 and 1541 drives are shipped from the factory se for device 8 The channel can be hard
11. disk CEMF is induced into the R W coil by the magnetic fields on the disk causing current flow which is detected by the read amplifiers Current flow through the R W coil will forward bias wither CR16 or CR17 depending on the direction Q7 and CR14 must be forward biased The first amplifier UF3 senses this current flow from the R W coil on one of the inputs and amplifies it L9 L10 L11 L12 and C45 act as a low pass filter suppressing noise on the amplified output UF4 is a differential amplifier which amplifies the difference of the two input signals from the filter section UE4 is a peak detector The output of UE4 will pulse high when a 1 is read This signal is then reconstruction of the data recorded The Time Domain Filter UD4 times out when a 1 bit has been read so unwanted 1 bits are not added to the actual data The One Shot UD4 generates the correct data pulse width so the PLA can convert the data to parallel for processor control 1541 CIRCUIT THEORY Write Amplifier Circuits During a write operation B must be high This forward biases Q7 and CR14 If B goes low Q3 and Q6 become forward biased If Q goes low Q5 and CR15 become forward biased passing current flow through R W 1 If goes low Q4 and CR 18 become forward biased passing current flow through R W 2 When a write operation occurs the ERASE coil is energized by forward biasing Q6 This demagnetizes the outer edges of the track preventing data
12. e adjusted by watching the 60Hz strobe as the adjustment is made or loading the system test from the diagnostic disc The Newtronics Motor Speed PCB is electronically the same as the ALPS Motor Speed PCB but some of the discrete components have been integrated TROUBLESHOOTING GUIDE NOTE Always check for latest ROM ECO upgrade If socketed IC is suspected bad be to check socket with ohmmeter SYMPTOM POSSIBLE SOLUTION No LED s on power up Is Power cord plugged into wall outlet correctly Is Power cord plugged in the disk drive correctly Check line fuse Check power switch Check clock on 6502 pin 37 Check 5 and 12 volt lines Error LED flashes on power up Check all RAM and ROM locations Error LED stays on all the time Check 6502 microprocessor Check ROMs Drive motor runs continuously Check 12V and red LED stays on Check 6502 logic gates logic array Drive motor runs continuously Check Rom and red LED stays off Check drive motor PCB Drive motor runs continuously Check VR2 5V Regulator with no red or green LED s Check Power Transformer After the drive warms up the Check 65225 motor runs continuously Check motor control PCB Loads programs with red LED Check drive speed flashing Check stepper motor Loading is intermittent Check ROMs Check drive alignment Does not load when hot or LED Check ROMs flashed 3 times Searches with LED flashing Check ROMs continuously Searching with no red LED C
13. ette in the area of a magnetic field Do not attempt to clean a diskette Do not touch the exposed area of a diskette DIAGNOSTIC and ADJUSTMENT procedures are outlined in detail on the diagnostic disk Commodore Part 31405101 A manual has been added to the diagnostic package It contain descriptions of testing procedures and adjustment methods OVERVIEW The drive itself an independent memory device THe drive is composed of a media clamp rotating mechanism a head positioning mechanism and an eject mechanism All positioning operations excluding insertion and removal of diskettes are controlled by the internal guide mechanism Closing the front door causes the media clamp mechanism to operate Two operations are performed in the following order a b The diskette is centered The diskette is clamped and retained between the spindle and the hub The spindle and hub rotates at 300 r p m through a closed loop control circuit employing a D C motor tachometer It is important that the relationship between the head and the media is maintained correctly during operation For this purpose a pressure pad is used to hold and press down the media about 12g from the opposite side of the head This head assembly is coupled by a metal band to a four base stepping motor which performs the track positioning One step of the stepping motor corresponds to a 1 2 track movement The control circuit on the logic board selects the direction and number o
14. f steps to the desired track The Read Write head uses a glass bonded ferrite ceramic head Track to track erasing is accomplished by the straddle erase method The surface of the Read Write head is mirror ground to minimize wear of the head and media Also the head is designed in such a way that the maximum signal can be obtained from the media surface The spindle drive motor operates on 12 VDC and turns the spindle through a belt drive at 300 revolutions per minute The speed of the drive motor is controlled by a feedback signal from a tachometer which is housed in the drive motor assembly The feedback signal controls a servo amp that supplies the 12 VDC drive current FLASH CODE The 1541 upon power up goes through its own internal diagnostic If an electronic problem is detected it s indicated by flash code The led s will blink a number of times pause and then flash again until the problem is corrected Number of flashes Possible failure 2 Zero page 3 4 DOS ROM s 5 6 7 8 RM Circuitry associated with these components can also cause the failure code Therefore it should be suspected as the next possible defect 1541 CIRCUIT THEORY All circuit diagrams have been taken from the short board schematic 1540049 unless otherwise noted The short board use a 6116 RAM which replaces the four 2114 I C s on the long board See page 11 for the Read Write logic differences The Power Supply The input AC voltage is c
15. heck 6522s logic gates logic array Message FILE NOT FOUND Clean drive head w alcohol is displayed Check 0 stop adjustment Check alignment Drive fails to read Check the 311 9602 and 592s There are two 12 volt sources for stepper output and read circuit make sure both are good TROUBLESHOOTING GUIDE continued SYMPTOM POSSIBLE SOLUTION Fails to format disk Check components related to connector P7 Check 6522s Check the logic array Stepper Motor does not step forward Check 6502 6522s logic array Drive speed will not stabilize Check DC motor Will not save when the drive Check 6502 microprocessor heats up Locks up when loading Check serial port components Check ROM Fails the performance test and Check test diskette displays a 21 read error Check Drive Motor Fails the performance test and Check stop adjust displays a 27 read error Passes performance test to Check read write head track 18 then displays 21 read error Passes the performance test but Check stepper motor will not load certain programs RESISTANCE CHECKS BROWN RED BLACK STEPPER MOTOR 9 YELLOW REG YELLOW TACH COLL SPINDLE MOTOR GHEY BLUE COIL RED WHITE ERASE COIL YELLOW 32 ohms end to centertap 64 ohms end to end Motor coil 17 ohms Tach coil 175 ohms at rest Tach coil 135 190 ohms in motion R W end to end 32 4 ohms R w end to centert
16. llel port YB0 YB7 The PLA contains a shift register which converts the parallel data into serial data The PLA generates signals on pins 2 3 4 and 40 which control the write amplifier circuits on D IN input on pin 24 of the PLA The PLA shift register converts serial data into parallel data that is latched at the parallel port Y B0 Y B7 The register converts serial data into parallel data that is latched at the parallel port YB0 Y B7 The microprocessor reads the parallel data that is latched at the parallel port YBO Y B7 The microprocessor reads the parallel PLA output by reading Port A of UC2 when BYTE READY on pin 39 goes low The stepper motor is controlled by two outputs on port B of UC2 STPO and STP1 A binary four count is developed from these two lines driving the four phases of the stepper motor The PLA converts STPO and STP1 into four outputs that represent one of the four states in the count Y0 Y1 Y2 Y3 The Spindle motor is controlled by the output MTR of UC2 The PLA inverts this signal It is then passed to the motor speed control pcb UC2 pin 14 is an input that monitors the state of the write protect sensor and pin 13 is an output that controls the activity light RED LED UC7 decodes the addresses output from the processor when selecting UC2 UC2 resides at memory locations 1800 180F 1541 CIRCUIT THEORY The circuit shown here is from the long board schematic 1540008 This logic was integrated in the PL
17. on one track from bleeding into the next track 1541 CIRCUIT THEORY u Power Up Down Write Protection This circuit prevents erroneous data from being written on the disk during power up down sequences During a power up the 12VDC supply is not applied to the R W coils and amplifier circuits before the processor has control of the logic During a power down the 12VDC supply is removed from the R w coils and amplifier circuits before the processor loses control of the logic Q1 acts as a series pass transistor biased to regulate the 12VF output to the R W coils and Amplifier circuits Q2 is a feedback amplifier monitoring the 5VDC supply CRS develops a precise reference voltage for Q2 L8 and C15 delay the 12VDC supply 1541 CIRCUIT THEORY V 1231 P5 BRANI PIN Spindle Motor Control Circuits _MTR output from the PLA is active low This signal is passed through the current driver UD2 to the motor control PCB When MTR is low QI is biased off and Q2 Q3 and O4 are biased on allowing current flow through the spindle motor coil Attached to the shaft of the spindle motor is an inductive tachometer that generates low level AC voltages as the motor spins The output of the tachometer is rectified by CR1 CR4 IC 1 monitors the output of the rectifier and adjusts the bias to Q2 which changes the bias on Q3 and Q4 to regulate motor current for a constant velocity VR1 is a manual speed adjustment The speed can b
18. ontrolled by switch 1 SW1 Disk circuit protection is provided by fuse 1 F1 If SW1 is closed the AC voltage input is applied to the primary winding of transformer one T1 T1 steps down th AC input voltage into two smaller AC voltages The top secondary AC output approx 16VRMS is converted to DC by the Full Wave Bridge Rectifier The DC output of CRI is regulated at 12VDC by VRI The bottom secondary AC output of T1 approx 9VRMS is converted to DC by the Full Wave Rectifier CR3 The DC output of is regulated at 5VDC by VR2 High frequency filtering is provided by and for the 12VDC supply and C4 C6 to C9 C22 C27 to C30 for the SVDC supply Low frequency filtering is provided by C17 and C2 for the 12VDC supply and C5 and C16 for the SVDC supply 1541 CIRCUIT THEORY 4 NA 4 0 P2 The Reset Circuit The output of the exclusive or gate UD3 pin 6 will be low until C46 has charged through R25 Once the voltage across C46 reaches 2 volts the output of UD3 pin 6 will go high This occurs when the disk is powered on or a reset pulse is generated by a device connected to the serial bus The reset pulse on the serial bus interface is Input on pin 6 of P2 or P3 This low to high going pulse on pin 6 of UD3 is input to the microprocessors reset interrupt input This causes a restart on reset routine to be executed giving control of the disk drive operation to the Disk Operating System DOS 15
19. ware altered to 9 10 or 11 by two methods 1 Refer to appropriate board layout drawing for the location of the pads provided for this purpose The device change pads must be CUT to alter the channel number and re soldered if another change is needed later 2 The preferred method to alter the device number is to lift certain pins of the 6522 chip The I C should always be socketed so removal of the chip is simple Once removed the proper pin can be carefully bent to eliminate it from the circuit If another change is needed simply remove the and re install with the pin back in place pence spari i eei Pagi eeu eS aa et d PCB ASSEMBLY 1540001 BOARD LAYOUT DEVICE NUMBER PAD LOCATION PIN CONFIGURATIONS 6502 KEELELE 901437 01 901435 01 Varsatie Interface Mictoprocessor Adapter VIA gt lt oo a amp G s Hitachi HM61161P 4 AP 20 Fs me ER i 3 fire y PRSE DA PCB ASSY 1540048 BOARD LAYOUT DEVICE NUMBER PAD LOCATION i er UPGRADE NOTES PCB Assembly 1540048 Schematic 1540049 requires an upgrade to the reset circuit The upgrade consists of 1 COMPONENT CHANGES R25 Change To 6 8K ohm 1 4 W 5 R57 Add 220 ohm 1 4 W 5 R58 Add 2K ohm 1 4 W 5 2 CUT circuit trace near UAI See diagram NOTE INSULATE WITH PROTECTIVE TUBING 01
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