Commodore C64 User manual

SERVICE MANUAL
MODEL C64 COMPUTER
FEB. 1985 PN-314001-02
Commodore Business Machines, Inc.
1200 Wilson Drive, West Chester, Pennsylvania 19380 U.S.A.
Commodore makes no expressed or implied war-
ranties with regard to the information contained
herein. The information is made available solely on
an as is basis, and the entire risk as to quality and
accuracy is with the user. Commodore shall not be
liable for any consequential or incidental damages
in connection with the use of the information con-
tained herein. The listing of any available replace-
ment part herein does not constitute in any case
arecommendation, 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 aretrieval system, or
transmitted in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise, without the prior written permis-
sion of Commodore Electronics Limited.
Copyright ©1985 by Commodore Electronics Limited.
All rights reserved.

CONTENTS
Title Page
SPECIFICATIONS
PRODUCT PARTS LIST
BLOCK DIAGRAM
CIRCUIT THEORY
POWER SUPPLY
1
2
3
RESET LOGIC
CLOCK CIRCUITS
I/O, ROM, EXPANSION PORT
RAM CONTROL LOGIC
5 PIN VIDEO AND AUDIO OUTPUTS
8PIN VIDEO AND AUDIO OUTPUTS
CASSETTE INTERFACE
KEYBOARD, JOYSTICK &PADDLE INTERFACES
SERIAL INTERFACE, USER PORT
TROUBLESHOOTING GUIDE
BOARD IDENTIFICATION
PCB ASSEMBLY #326298-01
4
5
6
7
8
9
10
11
12
13
14
17
BOARD LAYOUT 18
PARTS LISTS 19'20
PIN ASSIGNMENTS 21
SCHEMATIC #326106 21 '22
PCB ASSEMBLY #250407-04
BOARD LAYOUT 23
PARTS LIST 24'25
MODULATOR SCHEMATIC #251025 26
SCHEMATIC #251138 26'27
PIN ASSIGNMENTS 27
PCB ASSEMBLY #250425-01
BOARD LAYOUT 28
PARTS LIST 29'30
MODULATOR SCHEMATIC #251696 31
SCHEMATIC #251469 31 >32
PIN ASSIGNMENTS 32

C64
GENERAL DESCRIPTION
MEMORY
ROM
MICROPROCESSOR
DISPLAY
COLORS
CHARACTERS
DISPLAY MODES
RESOLUTION
SPRITES
SOUND
KEYBOARD
KEYS
INPUTS/OUTPUTS
FEATURES
PERIPHERALS
POWER REQUIREMENTS
COMPUTER
The "All Purpose" Commodore 64 is the complete computer for
education, home or small business applications. Supported by
quality peripherals and afull range of software, the Commodore 64
is perfect for the family. No other computer can offer such variety
of uses and applications at such an affordable price.
64K RAM
20K ROM Standard (includes operating system and BASIC
interpreter)
651 OA Microprocessor— 1.02 MHz clock •
the 6502
40 Columns X25 lines of text
16 Background, border and character colors
Compatible with
Upper &lower case letters, numerals and symbols
characters •All PET graphic characters
Reverse
Text characters
320 X200 Pixels
High resolution graphics
8independent sprites •Each consists of 24 X21 pixels and
up to 4colors •Each independently expandable horizontally
and vertically •Collision detection for sprite to sprite and data
to sprite collisions
•6581 Sound Interface Device includes 3independent tone
generators— each with 9octaves •Each voice includes
programmable ADSR generator (Attack, Decay, Sustain, Release)
and control of sawtooth, triangle, square, variable pulse and noise
waveforms •Full filtering capabilities with low, high and band
pass filters •External sound input
Full size typewriter style design
•66 Keys total •2Cursor control keys •
to 8user defined/programmable functions possible)
lower case character set •Graphic character set
4Function keys (up
•Upper and
•User port
paddle ports
Serial port
Video port ROM cartridge port •2Joystick/
C1530 Cassette drive interface port
•Built-in BASIC 2.0 —over 70 commands, statements and
functions •Full screen editor
•C1541 Disk drive •C1 530 Datasette
printer •MPS 802 Dot matrix printer •
printer •DPS 1101 Daisey wheel printer
Plotter/Printer •C1 702 Color monitor •
•120 Volts, 60 Hz
•MPS 801 Dot matrix
MPS 803 Dot matrix
•C1520
CM141 Color monitor
Specifications subject to change without notice
1

PARTS LIST
C-64
Commodore part numbers are provided for
indicate the availability of parts from Commodore. Industry standard parts (Resistors
Capacitors, Connectors) should be secured locally. Approved cross-references
Transistors, etc. will be available mmanual form trough the Service Department in November
jue or non-standard parts wilJ be stocked by Commodore and are indicated
the parts
TOP CASE ASSY
Top Case
Keyboard
LED Plate
Nameplate
Lamp Holder Set
LED Assembly
C326113-01
C326166-02
C326160-01
C326161-01
C903820-03
C1001039-01
BOTTOM CASE ASSY
Bottom Case
Foot, Self-Adhesive
PCB Shield Plate
PCB Insulation Sheet
C326114-01
C950157-04
C326131-01
C326288-01
ACCESSORIES
Users Manual
Power Supply
RF Cable
Switch Box
C320974
C251053-02
C326189-01
C904778-01
2

C-64 BLOCK DIAGRAM
CASSETTE
PORT
PADDLES
Imod r~
SYNC
CHROMA
LUMA
MONITOR
1MEG
Hz 00 ADDRESS
DECODING
PLA
DATA BUS
_
ADDRESS BUS
6526
CIA
KEYBOARD
MATRIX
EXPANSION
PORT
CONTROL
PORTS
3

There are three versions of the C64, The C64 with afive pin connector video output {326106),
The C64 with an eight pin connector video output {251 138}, and the C64B which has improved
system clock circuit design (251469). Most circuit theory explanations will be the same for all
three versions. Refer to schematic 326106 unless noted otherwise.
The Power Supply.
The external power supply generates aregulated 5VDC and 9VAC. 5VDC is applied to pins 5and
1of CN7 on the C64 pcb. Filtered by L5,C97, and C100 it is then controlled by on/off switch S1
.
This 5VDC output supplies the microprocessor logic.
9VAC is applied to pins 6and 7of CN7 on the C64 pcb. +12VDC, +5VDC CAN and 9VDC unregulated
are outputs that are derived from this 9VAC supply. The 9VAC supply is made available on pins 10
and 11of the USER PORT CN2.
12VDC Generation
9VAC is rectified by CR5. The unregulated DC output is filtered by C88 and C89 then regulated at
12VDC by VR1 .The regulated output is filtered by C57 and C59. The 12VDC supplies the VIC and
SID IC, and the audio amplifiers.
C64 CIRCUIT THEORY
VRl
+12
+S
C5S ±: :±' C57
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C°IO
CR5 470
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CAN +5
4CR4
M08
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JTcsi ^CS2
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-16V -
SHIELD GND
9VAC
POWER INPUT
(7 -PIN MALE DIN)CN7
+5VDC CAN Generation
9VAC is rectified by CR4. The unregulated DC output is filtered by C19, and C95 then regulated at
5VDC by VR2. The regulated output is filtered by C102 and C103. The output called 5VDC CAN
is separated and individually filtered into two outputs called Vvid and Vc. Vvid is the 5VDC supply
for the video circuits, and Vc is the 5VDC supply for the clock circuits.
9VDC Unregulated Generation.
CR6 rectifies the 9VAC input. The output is 9VDC unregulated, and not filtered. This supply powers
the cassette motor transistor amplifier circuits, and the RF modulator on the C64B version.
LI 2.ZMH
CAN +5
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25V -50V
20%
CAN +5CG5 ±L CGG_
1.47 I
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4

C64 CIRCUIT THEORY
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+5V
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+5V
CI05
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IK
U20 740&
Reset Logic Circuits.
U20 is a556 IC timer configured as aone shot multivibrator. The output pulse width is determined
by the size of R34 and C24. Pulse width =1.1 xR34 xC24 -.5 seconds. The output on pin 9
is "high" active. The output of U8 is "low" active. Reset initializes all the processor logic and causes
the processor to load the program counter register with the address of the first instruction of the
operating system program called the KERNAL. The starting address is stored in locations $FFFC and
$FFFD. The first instruction is decoded and executed giving KERNAL control of the computer opera-
tions. The reset pulse occurs when turning the power on to the computer.
5

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C64 CIRCUIT THEORY
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The C64 Clock Circuits.
Crystal Y1 develops a16MHz fundamental frequency clock signal. U31 is aDual Voltage Controlled
Oscillator. The output on pin 10 is a14.31818 MHz clock signal called the color clock. R27 can be
adjusted to obtain exact output frequency. U30 is afrequency divider that outputs a2MHz signal
on pin 6. U29 is aDflip flop which outputs a1MHz signal on pin 9. U32 is aPhase/Frequency Detec-
tor which compares the output of the U29 to the phase clock, and outputs adc voltage on pin
8that is proportional to the phase difference between the inputs. The second half of the Dual Voltage
Controlled Oscillator U31 generates an 8.1818MHz clock signal called the DOT Clock. The VIC IC
divides the DOT clock by eight and outputs this as the phase clock on pin 17. The output of the
Phase/Frequency Detector is applied to the frequency control input pin 2of U31 .This causes track-
ing of the dot clock and the color clock because one input, pin 3of U32, is the phase clock which
is derived from the dot clock, and the other input pin 1of U32, is derived from the color clock.
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The C64B Clock Circuits. Refer to schematic 251469
Crystal Y1 develops the fundamental 16MHz clock signal. U31 is aClock Generator IC that outputs
the 8.1818MHz DOT clock on pin 6, and the 14.31818 MHz color clock on pin 8.
6

C64 CIRCUIT THEORY
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CARTRIDGE /EXPANSION (44 -PiNJ FEMALE) CN&
I/O and ROM Address Decoding and Expansion Port.
I/O Address Decoding Logic.
U17 is aProgrammable logic array (PLA). The output F5 on pin 12 called I/O goes 'Mow" when any
of the I/O devices controlled by U15 are selected. The addresses are listed below for each device.
VIC IC
SID IC
Color Ram
CIA1
CIA2
I/O 1
I/O 2
$D000 -$D02E
$D400 -$D7FF
$D800 -$DBFF
$DC00 -$DCOF
$DDOO -$DDOF
$DEOO -$DEFF
$DFOO -$DFFF
ROM Address Decoding.
"low"
Basic ROM resides at locations $A000 -$BFFF. The output F1 pin 17 of the PLA U17 goes
when the BASIC ROM is selected. The KERNAL ROM resides at locations $E000 -$FFFF. The output
F2 pin 16 of the PLA U17 goes "low" when the KERNAL ROM is selected. The CHARACTER
GENERATOR ROM resides at locations $D000- $DFFF. The output F3 pin 15 of the PLA U17 goes
"low" when the Character Generator ROM is selected.
The Expansion Port Connections.
The expansion port is an extension of the microprocessor address, data, and control bus. ROML decodes
addresses $8000 -$9FFF, and ROMH decodes addresses $E000 -$FFFF. These are outputs from
the PLA used to select the cartridge inserted in the expansion port. I/O 1input from U15 decodes
addresses $DE00 -$DEFF. I/O 2output from U15 decodes addresses $DF00 -$DFFF.
7

C64 CIRCUIT THEORY
R-31
180-a
+5
SYWCii
LUM
RAM Control Logic.
U13 and U25 are multiplexers. The address outputs from the microprocessor are passed to RAM via
U1 3and U25 when the output Address Enable Control (AEC) from the VIC IC is "high". When AEC
is "low" the VIC IC outputs refresh addresses on pins 24-31. AEC goes "low" when the system
clock, phase 2, is "low". Since all I/O decoding occurs when phase 2is "high", refresh is transparent
to the processor.
Eight 41 64 DRAMS provide 64k bytes of memory. One 2114 RAM (U6) provides 51 2bytes of memory
allocated for screen color data storage.
8

C64 CIRCUIT THEORY
1,47
AC
A5/AI3
A4/A1Z
Vdd
SYK1C15.
LUM
A3/AM
A2/AIO
AI/A9
AO/A8
AEC
COLOR A
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BA
FBI5 CR3
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CAPIB
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AUDIO
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MODULATOR
CASE 4
VIDEO AUDIO
5 Pin Video and Audio Output Circuits.
Pin 15of the VIC IC is the sync/luminance output. Pin 14is the color output. Acomposite video out-
put is created by mixing sync/luminance and color. The composite output is applied to the RF modulator,
and also passed to the monitor connector CN5 on pin 4. The color output is not made available on
the monitor connector CN5 as on the 8pin version, and the RF modulator mixes audio with the com-
posite video producing the TV RF output, unlike the 8pin version RF modulator which creates the
composite video output.
9

C64 CIRCUIT THEORY
<jBr*Wip)
**>rei.
U1 9is the Video Interface Chip (VIC). Sync (horizontal and vertical), and luminance (video) is output
on pin 15. This signal is passed to pin 2of the RF modulator. Color is output on pin 14, and passed
to pin 3of the modulator. Light Pen inputs are sensed by the VIC IC on pin 9. U1 8is the Sound Inter-
face Device IC (SID). The audio output is on pin 27, and audio input is on pin 26. The RF modulator
mixes sync/luminance, color, and audio out, generating aTV composite signal on pin 2. The RF
modulator also passes the VIC outputs to the monitor connector CN5. Audio out on pin 27 is amplified
by Q2, and output on pin 3of CN5. Audio in is applied to pin 5of CN5, then to pin 26 of the SID
IC. Inputs from paddles connected to one of the control ports are monitored by the SID IC on pins
23 and 24.
10

RP3 3.3K Rl 3<3K QASS MOTOR
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P3P4P5 Vcc AEC
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A13
A12
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AIO
A9
A8
A7
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A4
A3
A2
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D7
DC
D5
04
D3
D2
01
DO
oIN
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CA55 RD
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PAO
PA I
PA2
PA3
PA4
PA5
PAG
PA7
PBO
P6I
PB2
PB3
PB4
PB5
PB£
PB7
CNT
SP
CIA
(DCOO-
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D7
DG
D5
D4
D3
02
01
DO
RS3
RS2
RSI
RSD
IRQ
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C64 CIRCUIT THEORY
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The Cassette Interface Circuits.
U7 is a6510 microprocessor. One of the features of the 6510 is abuilt in parallel I/O port (P0-P5).
P3 -P5 control most of the cassette interface circuitry. P3 pin 26 of U7 outputs the write data signal
to connector CN3 on pins Eand 5. P4 is an input that senses the play switch depressed on the cassette
deck. P5 is an output that controls the cassette motor. When P5 goes "low", Q2 cuts off, CR2 regulates
Vb of Q1 at 7.5 volts, this forward biases Q1 and Q3, passing current through the cassette motor
coil. U1 is aComplex Interface Adapter (CIA). Parallel ports, serial outputs, and Timers are standard
features of the CIA. Read data enters on pins D, 4of CN3. U1 accepts the read data signal on the
FLAG input pin 24.
11

C64 CIRCUIT THEORY
CARTRIDGE EXPANSION
CNG
PA
1
3
5
1
W
R
2
CTRL
A
D
7
STOP
SHIFT
4
SPACE
Z
X
7
9
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P
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DEL RET
V
C
B
IM
5
SB
6
s
F
H
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CRSR A
CRSR
SHIFT
F1
Q
E
T
U
3
2
3
4
6
8
K
F3
O
F5
CLR
F7
L_J RESTORE
U20
5V >6510
KEYBOARD MATRIX
Keyboard, Joystick, and Paddle Interface Circuits.
Keyboard Interface.
U1 is aComplex Interface Adapter (CIA). Both parallel ports are used to decode the keyswitches on
the keyboard. Parallel port Asignals (PAO -PA7) are outputs. Parallel port Bsignals (PBO -PB7) are
inputs. A"0" bit is shifted through the parallel port A, when akey is depressed on the keyboard,
the "0" bit is returned on one of the parallel port Binputs. Aprogram in the KERNAL ROM generates
the shifting "0" bit output on parallel port A, and decodes the signals returning on the parallel port
Binputs. Depressing the restore key causes U20 to trigger. U8 pin 6goes
Maskable Interrupt (NMI) at the processor. This causes the processor to execute asubroutine which
initializes the I/O Interfaces. If the STOP key is depressed at the same time, BASIC flags are also
initialized.
'"ow" generating aNon-
Joystick Interface.
U1 also controls the joystick. Parallel port Aaccepts inputs from the Bjoystick connected to control
port 2. Parallel port Baccepts inputs from the Ajoystick connected to control port 1.When the joystick
is moved up, down, left, right, or the fire button is depressed, aground potential is applied to the
appropriate input of U1.
Paddle Interface.
AVariable resistor is connected to adjusting knob on the paddle. When the knob is rotated, the
resistance varies controlling the time constant of an RC network. The Voltage developed across the
capacitor is input to an A/D converter internal to the SID chip U18. The digital output is stored in
one of the SID registers. The paddle position can be determined by the reading the contents of the
appropriate register. U28 is a4066 CMOS switch. The signals from the paddles are passed to the
SID chip when the Enable inputs (EO -E3) of U28 are "high".
R50TE: U1 port assignments are incorrect on
schematics. Refer to Keyboard Matrix
for correct assignments. 12

C64 CIRCUIT THEORY
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The Serial Interface and User Port Circuits.
The Serial Interface.
U2 is aComplex Interface Adapter (CIA). Parallel port signals PA3-PA7 control the serial bus inter-
face. PA3 is the Attention (ATN) output. This signal is inverted by U8 before being transmitted to
adevice on the bus. PA4 is the Clock output. Data transmitted from the C64 to adevice on the bus
is synchronized by this clock signal. U8 inverts the output PA4. PA5 is the data output. U8 inverts
this output also. Data transmitted from adevice on the bus to the C64 is synchronized by aclock
generated by the transmitting device. The Clock signal is input on PA6. Data transmitted from adevice
on the bus to the C64 is input on PA7. When adevice on the bus wants to communicate with the
C64, SRQ IN goes 'Mow" indicating service is requested.
The User Port.
Parallel port Bof U2 (PBO -PB7) is made available on the user port. Parallel data transfers with exter
nal devices are made very easily through this parallel port. SP2 and SP1 are bi-directional serial ports
CNT1 and CNT2 are bi-directional synchronizing clock signals for each serial port.
13

64 TROUBLESHOOTING GUIDE
SYMPTOM
Blank screen on power up.
Out of memory error on power up.
No cursor displayed.
Intermittent blank screen.
Intermittent graphics.
Powers up with graphic display and
blinking cursor.
Powers up with all the characters
displayed as blocks.
Intermittent display.
Powers up with 'PRESS PLAY ON
TAPE' message and the display blanks.
On power up the cursor locks up.
When 'RETURN' is pressed after arun
command, the cursor goes back to
home position.
Poke command does not work.
Joystick does not operate correctly.
Wrong frequency.
No character lettering is displayed on
the screen.
Graphic characters instead of letters
displayed.
Power up message appears but no
cursor.
POSSIBLE SOLUTION
Check External Power Supply
U4 (KERNAL ROM), U17 (PLA)
U7 (6510 MPU), U3 (ROM)
U8 (7406 IC), U19 (VIC II)
U9-U12 (4164 RAM)
U21-U24 (4164 RAM)
VR2, CR4, VR1
Check U9-U12 (4164 RAM)
U21-U24 (4164 RAM)
**** USE DIAGNOSTIC TEST DISK
Check U7 (6510 MPU)
Check U14 (74LS258 IC)
Check U26 (74LS373 IC)
Check C88 (Possible Bad Connection)
Check U7 (6510 MPU)
R1 (Possible Bad Connection)
Check U7 (6510 MPU)
U20 (556 IC)
Check U3 (ROM)
Check U3 (ROM)
Check U1 (6526 CIA)
Check C70
Check U3 (ROM)
U2 (CIA)
Check U19 (VIC
Check U4 (ROM)
14

64 TROUBLESHOOTING GUIDE (Continued)
SYMPTOM
Cursor jumps back to home position.
Abnormal colors appear in the letters
Different characters are displayed and
cursor is locked when turned on and
off.
System does not reset and the
'RESTORE' key does not work.
White band scrolls down the screen.
(60 HZ HUM)
Cursor disappears after the system
warms up.
SYNTAX ERROR displayed after
system warms up.
Wavy screen after the system warms
up.
The system resets when it warms up
and long programs do not load.
Keyboard does not operate correctly
when the system warms up.
Black band scrolls through screen
when system warms up.
Cassette motor keeps running.
Cassette motor keeps running even
after aprogram is done loading. The
TIP 29 transistor gets extremely hot
and the fuse may possibly blow.
The cursor disappears when the
cassette is plugged in.
Cassette runs extremely slow. The
program
run.
seems to load but will not
POSSIBLE SOLUTION
Check U7 (6510 MPU)
Check U6 (2114 RAM)
U16 (4066 IC)
Check U16 (4066 IC)
Check U20 (556 IC)
Check External Power Supply
VR2 (5V Regulator)
Check U1 (6526 CIA)
Check U3 (ROM)
Check External Power Supply
U31 (74LS629 IC)
U30 (74LS193 IC)
Check U7 (6510 MPU)
U3 (ROM)
Check U1 (6526 CIA)
U3 (ROM)
Check External Power Supply
C90, C88, CR4
VR2 (5V Regulator)
Check U7 (6510 MPU)
Check Cassette Port for Shorts
R4 (Possibly Open)
Check U7 (6510 MPU)
Check U7 (6510 MPU)
15

64 TROUBLESHOOTING GUIDE (Continued)
SYMPTOM
When loading from acassette,
'SYNTAX ERROR' message is
displayed.
the
DEVICE NOT PRESENT ERROR is
displayed when disk is used.
Disk drives continue to search when
trying to load.
When loading from disk and any key of
the 4th row of the keyboard is
pressed, the cursor goes to home
position.
When loading from disk, a'FILE NOT
FOUND' message is displayed.
OUT OF MEMORY ERROR is displayed
when disk is used.
POSSIBLE SOLUTION
Check U20 (556 IC)
Check U1 (6526 CIA)
U7 (6510 MPU)
R28, R29, R30
Check U2 (6526 CIA)
Check U20 (556 IC)
R35 (Possible Bad Connection)
Check U4 (ROM)
U2 (6526 CIA)
Check U20 (556 IC)
16

C64 BOARD IDENTIFICATION
To date there are 4versions of 64 PCB assemblies in use.
VERSION
Original
A(CR)
B
B-2
IDENTIFYING FACTORS
5pin board
(CN5-Video port has 5pins)
8pin board
(CN5-Video port has 8pins)
8pin board
(Reduced oscillator circuit)
8pin board
(Reduced Osc. w/component changes)
PCB ASSY #
326298-01
250407-04
250425
250441-01*
SCHEMATIC #
326106
251138
251469
251469
These boards are interchangeable with casework, keyboard, etc.; however, care must be taken
to provide the customer with aunit that is compatible with their monitor and cable.
When component level repairs are necessary, be certain to acquire the appropriate part for the
board you are repairing. Most modulators are different, as are many of the other components.
*The 4th version of 64 board was recently developed and only afew may be in the field. It is termed
the 64B-2. All circuits remain the same as the 64B (Schematic 251 469) with afew component loca-
tion changes:
1) Resistors 28, 29, 30, 36, 48 were reduced to Resistor Pack RP5.
2) Diodes CR100-105 are no longer piggybacked. Their new locations are CR9, 12-16.
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BOARD LAYOUT #326298-01
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