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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 or guaranty as

to quality or suitability of such replacement part. 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.

Summary of content (33 pages)

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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.
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CONTENTS • • • • • • • • • • • • • • • • • SPECIFICATIONS BLOCK DIAGRAM CARE AND MAINTENANCE OVERVIEW FLASH CODE 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 AND MOTOR CONTROL LOGIC o READ/WRITE CONTROL LOGIC o READ AMPLIFIER o WRITE AMPLIFIER o POWER UP/DOWN WRITE PROTECTION o STEPPER MOTOR CONTROL CIRCUITS o SPINDLE MOTOR CONTROL CIRCUITS TROUBLESHOOTING GUIDE RESISTANCE CHECKS CASEWORK/ACCESSORY PARTS L
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C1541 DISK DRIVE PRODUCT SPECIFICATION GENERAL DESCRIPTION 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 MAXIMUM STORAGE 170K of data (formatted) - 35 tracks MEDIA 5-1/4 Inch floppy disk.
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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.
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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) The diskette is centered. b) The diskette is clamped and retained between the spindle and the hub.
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1541 CIRCUIT THEORY The Power Supply The input AC voltage is controlled 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 CR1. The DC output of CR1 is regulated at 12VDC by VR1. The bottom secondary AC output of T1 (approx.
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The Clock Circuits Crystal Y1 outputs a 16Mhz clock signal. THis is input to UD5 on pin 8. UD5 is configured as a ÷ 16 frequency divider. The output of UD5 pin 12 is a 1 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).
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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. UC5 and UC6 decodes the addresses output from the microprocessor when selecting these ROMS. UB2 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.
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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 (PB0PB7) 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 CA1 of UC3 after being inverted by UA1.
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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 parallel 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.
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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 UF5 pin 4. UF5 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, Q and _Q, 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 'NOR' gate UE5.
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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.
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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 _Q goes "low", Q4 and CR18 become forward biased, passing current flow through R/W 2. When a write operation occurs, the ERASE coil is energized by forward biasing Q6.
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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.
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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," Q1 is biased off, and Q2, Q3, and Q4 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.
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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.
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displays a 21 read error. Check Drive Motor. Fails the performance test and displays a 27 read error. Check stop adjust. Passes performance test to track 18 then displays 21 read error. Check read/write head. Passes the performance test but will not load certain programs. Check stepp RESISTANCE CHECKS 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 centertap = 16.
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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 1541 MODEL IDENTIFICATION PCB Assy # 1540008-01
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DEVICE NUMBER CHANGE The 1540 and 1541 drives are shipped from the factory se for device # 8. The channel can be hardware 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.
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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 UA1 (See diagram) 3) INSTALL JUMPER WIRES: BETWEEN: UA1 pin 8 and UB1 pin 5 UA1 pin 9 and CR4 Anode UB1 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.
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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.
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PARTS 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 6. 7. 8. 9. 4.
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ALPS DRIVE ASSEMBLIES 1540/1541
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SYMBOLDESCRIPTION I.C. Q1 Q2 Q3 Q4 Sony CX-065B Transistor 2SC2785 Transistor 2SC2785 Transistor 2SA1175 Transistor B703-Q36E CR1,2,3,4,5 R1,7 R2 R3 R4 R5 R6 R8 R9 R10 VR1 Diode IN4148 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 R. 20 kOhm C1,5,6Cap.Electrolytic 10µF C2 Capacitor 0.0047µF C3 Capacitor 0.033µF C4,9 Cap.Tantalium 0.
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