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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. 

Copyright © 1985 by Commodore Electronics Limited. 
All rights reserved. 



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 LIST 
MODEL INDENTIFICATION 
DEVICE NUMBER CHANGE 
PC ASSEMBLY 1540001 

o BOARD LAYOUT 

o PARTS LIST 

o PIN CONFIGURATIONS 

o SCHEMATIC 
PC ASSEMBLY 1540048 

o BOARD LAYOUT 

o PARTS LIST 



o UPGRADE NOTES 
o SCHEMATIC 

• PC ASSEMBLY 250442, 250446 

o BOARD LAYOUT 

o PARTS LIST 

o IC PINOUTS AND INTERNAL DIAGRAMS 

o SCHEMATIC 

• POWER SUPPLY ASSEMBLY 1 54002 

o PARTS LIST 

o TRANSFORMER 

o ASSEMBLY DRAWING 

• ALPS DRIVE ASSEMBLY 

o PARTS LIST 

o WIRING DIAGRAM AND LAYOUT 

o MOTOR CONTROL PCB SCHEMATIC 

• NEWTRONICS DRIVE ASSEMBLY 

o PARTS LIST 

o WIREsfG DIAGRAM AND LAYOUT 

o MOTOR CONTROL PCB SCHEMATIC 



C1 541 DISK DRIVE 
PRODUCT SPECIFICATION 



GENERAL DESCRIPTION 



MAXIMUM STORAGE 
MEDIA 

INPUT/OUTPUT 

CONTROLLER 

MEMORY 

DATA TRANSFER RATE 

FILE TYPES 

NUMBER OF FILES 

COMPUTERS 

MEDIA COMPATIBILITY 

POWER REQUIREMENTS 

POWER CONSUMPTION 



The CI 541 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 

5-1/4 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 - 1 MHz clock 

2KRAM, 16KROM 

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, CI 6 

2031,4040, C1551,C1571 

120 Volts AC, 60Hz - integral power supply with external 1 Amp fuse 

30 Watts maximum 



SPINDLE 
MOTOR 



R.'W HEAD 



STEPPER 
MOTOR 



+ I 2± 1 4- 



SPINDLE MOTOR 
SPEED COMTHOL 

pea. 




\ 

WRITE 
PflOTECT S^NSOft 



SPINDLE 

□ RIVE 
CIRCUITS 



A e 



STEPPER 

OftlVE 
CIRCUITS 



READ 

WHITE 

CIRCUITS 



MAiN PAINTED CIRCUIT 



AC IN 

=0= 



® 



SEfttAL 
INT 



ACTIVITY 
LED 



ATM 



OATA 



POWER 
SUPPLY 



*-S POWER ON 



• 



• 



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 diskette 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) 

The diskette is centered, 
b) 

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 of 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 RAM 



Circuitry associated with these components can also cause the failure code. Therefore, it should be suspected as 
the next possible defect. 



1541 CIRCUIT THEORY 



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J I* 



^ mum 



All circuit diagrams have been taken from the short board schematic 1540049 unless 
otherwise noted. The short board use a 61 16 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 controlled by switch 1 (SW1). Disk circuit protection is provided by fuse 1 (Fl). If SW1 
is closed, the AC voltage input is applied to the primary winding of transformer one (Tl). Tl 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 Tl (approx. 9VRMS) is converted to DC by the Full Wave Rectifier CR3. The DC 
output of CR3 is regulated at +5VDC by VR2. High frequency filtering is provided by CI and C3 for the 
12VDC supply, and C4, C6 to C9, C22, C27 to C30 for the 5VDC supply. Low frequency filtering is provided 
by C17 and C2 for the 12VDC supply, and C5 and CI 6 for the 5VDC supply. 



1541 CIRCUIT THEORY 




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j r* rt * 



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). 



1541 CIRCUIT THEORY 



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The Clock Circuits 

Crystal Yl outputs a 16Mhz clock signal. THis is input to UD5 on pin 8. UD5 is configured as a -s- 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, -5- 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 



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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. UC5, UC6 and UC7 decode the addresses output from the 
processor when selecting RAM. 



1541 CIRCUIT THEORY 




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 CA1 of UC3 after being inverted 
by UA1. 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 UB1. UC3 is selected by UC7 pin 7 going 
"low" when the proper address is output from the processor. UC3 resides at memory locations $1C00-$1C0F. 



1541 CIRCUIT THEORY 

lEil :JL 




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. The PLA shift register converts serial data into parallel 
data that is latched at the parallel port (YB0-YB7). The register converts serial data into parallel data that is 
latched at the parallel port (YB0-YB7). The microprocessor reads the parallel data that is latched at the parallel 
port (YB0-YB7). 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 




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as 



^ 



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The circuit shown here is from the long board schematic 1540008. This logic was integrated in the PLA 
(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 
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 TSTOR' gate UE5. UE5 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 



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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. 

R/W HEAD 



R/W 1 <^- 



CQWl 0- 



R/W 2 o- 



EflASf t>- 



o: 



j 






R/W 
COIL 



RASE 



} ERAS 

J COIL 



When data is being read from the 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, LI 1, 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 _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. This 
demagnetizes the outer edges of the track, preventing data on one track from bleeding into the 
next track. 



1541 CIRCUIT THEORY 



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+tl 






♦ +I2VF 



H 



?SC«45 




+5 



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. 

Ql 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. CR5 develops a 
precise reference voltage for Q2. L8 and C15 delay the 12VDC supply. 



1541 CIRCUIT THEORY 



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MTR 



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9 




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+ 1IV PS 
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C + MOTOR 
OUT 

O- MOTOR 
OUT 

rsiui 



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," Ql 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. 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 be 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 
and red LED stays on. 


Check +12V. 

Check 6502, logic gates, logic array. 


Drive motor runs continuously 
and red LED stays off. 


Check Rom 

Check drive motor PCB. 


Drive motor runs continuously 
with no red or green LED's. 


Check VR2 (5V Regulator) 
Check Power Transformer. 


After the drive warms up the 
motor runs continuously. 


Check 6522s. 

Check motor control PCB. 


Loads programs with red LED 
flashing. 


Check drive speed. 
Check stepper motor. 


Loading is intermittent. 


Check ROMs. 

Check drive alignment. 


Does not load when hot or LED 
flashed 3 times. 


Check ROMs. 


Searches with LED flashing 
continuously. 


Check ROMs. 


Searching with no red LED. 


Check 6522s, logic gates, logic array. 


Message 'FILE NOT FOUND' 
is displayed 


Clean drive head w/alcohol. 
Check stop adjustment. 
Check alignment. 


Drive fails to read. 


Check the 3 1 1, 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 

heats up. | 


Check 6502 microprocessor. 


Locks-up when loading. 


Check serial port components. 
Check ROM. 


Fails the performance test and 
displays a 21 read error. 


Check test diskette. 
Check Drive Motor. 


Fails the performance test and 
displays a 27 read error. 


Check stop adjust. 


Passes performance test to 
track 1 8 then displays 2 1 read 
error. 


Check read/write head. 


Passes the performance test but 
will not load certain programs. 


Check stepper motor. 



RESISTANCE CHECKS 

BROWN 






STEPPER 
MQTGF 






HED 



SLACK 



YELLOW 



RED 



ORANGE 



32 ohms end to centertap 
64 ohms end to end 



SPIN DIE 
MOTOR 




REt? 



VELLOW 



TACH COLL 



BLLTS 



Motor coil = 17 ohms 

Tach coil = 175 ohms at rest 

Tach coil = 135 - 190 ohms in motion 



COIL 



ERASE 
COIL 



I 



SLUE 



FED 
' WHITE . 



■YELLOW 



R/W end to end = 32.4 ohms 
R/w end to centertap = 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 
LED ASSEMBLY 
SELF ADHESIVE FOOT 

1540 NAMEPLATE 

1541 NAMEPLATE 
POWER CORD ASSEMBLY 
6 PIN DIN CABLE 
USER'S MANUAL 
DEMO DISKETTE 



1540013-03 
C 1540013 
C 950150-02 
C 1540016-02 
C 1540052-00 
C 903508-04 
C 1515001-01 
C 1540031-03 
C 1540024-01 



NOTE: All 1540 Disk Drives were manufactured prior to any changes to the board and used the Alps drive 
exclusively. 



PCB Assy# 1540008-01 



PCB Assy #1540048 



1541 MODEL IDENTIFICATION 

Schematic* 1540001 
Original "Long" Board 
Has 4 discreet 2114 RAMs 
ALPS Drive only 

Schematic* 1540049 
Referred to as the CR board 
Changed to 2048 x 8 bit RAM pkg. 
A 40 pin Gate Array is used 
Alps Drive (-01) 
Newtronics Drive (-03) 

Schematic #251748 
Termed the 1541 A 
Just one jumper change to accommodate both types of drive 

Schematic # 251748 (See Notes) 
Termed the 1541 A-2 

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 



PCB Assy #250442-01 



PCB Assy #250446-01 



down" door and Newt: 



onics 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 hardware altered to 
# 9, 10, or 1 1 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 I.C. and re-install with the pin back in place. 



PCB ASSY # 


LOCATION | |DEVICE # 


LIFT PIN 


1540008 


UAB1 9 


15 


1540048,251748 


UC3 10 


16 


and 251834 


UC3 11 


15 and 16 



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PIN CONFIGURATIONS: 



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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, +1-5% 
R57Add 220 ohm, 1/4 W, +1-5% 

R58 Add 2K ohm, 1/4 W, +1-5% 



2) CUT circuit trace near UA1 (See diagram) 




NOTE: INSULATE WITH PROTECTLVE TUBING 



H58-.2KSJ 



CUT TBACE 



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, 1.0A 903556-16 
POWER TRANSFORMER 1540009-02 



POWER SUPPLY 
#1540002 



SHIELD WIRE 
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INPUT 




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ASSEMBLY DRAWING 



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 

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 




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MOTOR CONTROL P.C.B. 



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SYMBOL DESCRIPTION 



Sony CX-065B 
Transistor 2SC2785 
Transistor 2SC2785 
Transistor 2SA1 175 
Transistor B703-Q36E 
Diode IN4 148 
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, lOuF, 35V 
Capacitor, 0.0047uF, 50V 
Capacitor, 0.033uF, 50V 
Capacitor, Tantalium, 0.47uF, 35V 
Capacitor, Tantalium, 2.2uF, 16V 
Capacitor, 0.068uF, 50V