Commodore C64 Service Manual

SERVICE MANUAL

MODEL C64 COMPUTER

SEPTEMBER 1985 PN-314001-02

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.

Converted to PDF: [e-mail] in Jan.2007

• SPECIFICATIONS

• PRODUCT PARTS LIST

• BLOCK DIAGRAM

• CIRCUIT THEORY

o POWER SUPPLY

o RESET LOGIC

o CLOCK CIRCUITS

o I/O, RAM, EXPANSION LOGIC

o RAM CONTROL LOGIC

o 5 PIN VIDEO AND AUDIO OUTPUTS

o 8 PIN VIDEO AND AUDIO OUTPUTS

o CASSETTE INTERFACE

CONTENTS

o KEYBOARD, JOYSTICK & PADDLE INTERFACES

o SERIAL INTERFACE, USER PORT

• TROUBLESHOOTING GUIDE

• BOARD IDENTIFICATION

• PCB ASSEMBLY #326298-01

o BOARD LAYOUT

o PARTS LISTS

o SCHEMATIC #326106

• PCB ASSEMBLY #260407-04

o BOARD LAYOUT

o PARTS LIST

o MODULATOR SCHEMATIC #251025

o SCHEMATIC #251138

• PCB ASSEMBLY #250425-01

o BOARD LAYOUT

o PARTS LIST

o MODULATOR SCHEMATIC #251696

o SCHEMATIC #251469

o PIN ASSIGNMENTS

C64 COMPUTER

GENERAL DESCRIPTION

MEMORY

ROM

MICROPROCESSOR

DISPLAY

COLORS

CHARACTERS

DISPLAY MODES

RESOLUTION

SPRITES

The "All Purpose" Commodore 64 us the complete computer for education,
home or small business applications. Supported by quality peripherals and a full
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)

6510A Microprocessor - 1.02 MHz clock
Compatible with the 6502

40 Columns X 25 lines of text

16 Background, border and character colors

Upper & lower case letters, numerals and symbols
Reverse characters
All PET graphic characters

Text characters
High resolution graphics

320 X 200 Pixels

8 independent sprites
Each consists of 24 X 21 pixels and up to 4 colors
Each independently expandable horizontally and vertically
Collision detection for sprite to sprite and data to sprite collisions

SOUND

KEYBOARD

KEYS

INPUTS/OUTPUTS

FEATURES

PERIPHERALS

6581 Sound Interface Device includes 3 independent tone generators - each
with 9 octaves
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
2 Cursor control keys
4 Function keys (up to 8 user defined/programmable functions possible)
Upper and lower case character set
Graphic character set

User port
Serial port
ROM cartridge port
2 Joystick/paddle ports
Video port
C1530 Cassette drive interface port

Built-in BASIC 2.0 - over 70 commands, statements and functions
Full screen editor

C1541 Disk drive
C1530 Datasette
MPS 801 Dot matrix printer

MPS 802 Dot matrix printer
MPS 803 Dot matrix printer
DPS 1101 Daisey wheel printer
C1520 Plotter/Printer
C1702 Color monitor
CM141 Color monitor

POWER REQUIREMENTS

120 Volts, 60 Hz

Specifications subject to change without notice.

PARTS LIST

C-64

PLEASE NOTE: Commodore part numbers are printed for reference only and do not indicate the availability of
parts from Commodore. Industry standard parts (Resistors, Capacitors, Connectors) should be secured locally.
Approved cross-references for TTL-chips, Transistors, etc. will be available in manual form through the Service
Department in November of 1984. Unique or non-standard part will be stocked by Commodore and are indicated
on the parts list by a "C".

TOP CASE ASSY

Top Case

Keyboard

LED Plate

Nameplate

Lamp Hold Set

LED Assembly

BOTTOM CASE ASSY

Bottom Case

Foot, Self-Adhesive

PCB Shield Plate

PCB Insulation Sheet

ACCESSORIES

Users Manual

Power Supply

RF Cable

Switch Box

C 326113-01

C 326166-02

C 326160-01

C 326161-01

C 903820-03

C 1001039-01

C 320974

C 251053-02

C 326189-01

C 904778-01

C 326114-01

C 950157-04

C 326131-01

C 326288-01

C64 CIRCUIT THEORY

There are three versions of the C64. The C64 with five pin connector video output
(326106). The C64 with an eight pin connector video output (251138), 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 a regulated 5VDC and 9VAC. 5VDC is applied to pins 5 and 1 of 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 6 and 7 of CN7 on the C64 pcb. +12VDC, +5VDC CAN and 9VAC
unregulated are outputs that are derived from this 9VAC supply. The 9VAC supply is made
available on pins 10 and 11 of the USER PORT CN2.

12VDC Generation

9VAC is added to 9VDC through CR6, and 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.

+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 video circuits, and Vc is
the 5VDC supply for the clock circuits.

9VDC Unregulated Generation

CR4 rectifies the 9VAC input. The output is 9VDC unregulated. This supply powers the cassette motor transistor
amplifier circuits, and the RF modulator on the C64B version.

C64 CIRCUIT THEORY

Reset Logic Circuits

U20 is a 556 timer configured as a one shot multivibrator. The output pulse width is determined by the size of
R34 and C24. Pulse width = 1.1 x R34 x C24 = .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 decode and executed giving
KERNAL control of the computer operations. The reset pulse occurs when turning the power on to the computer.