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Commodore 64 / 64C Service Manual

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Revision as of 17:34, 1 October 2026 by Josh (talk | contribs) (Remove link to the (1985 Feb) title, now a redirect to the March page)

The Service Manual C64/C64C (March 1992, PN-314001-03) is Commodore Business Machines' service manual for the Commodore 64 and Commodore 64C. The title page carries a 1992 Commodore Electronics Limited copyright. It has 42 numbered pages; the 57-page scan adds the covers, blank fold-out backs and Commodore's document change and registration forms. The scan has a text layer for the typed pages; the parts lists for the B-3 and E boards, the pin assignment pages and the schematics are images.

Boards covered

Assemblies in the manual
Version Assembly Schematic Pages
Original (5-pin video) 326298-01 326106 Layout p. 18, parts list pp. 19-20, pin assignments and schematic pp. 21-22
A (CR) (8-pin video) 250407-04 251138 Layout p. 23, parts list pp. 24-25, schematics pp. 26-27
B 250425-01 251469 Layout p. 28, parts list pp. 29-30, schematics pp. 31-32
B-2 250441-01 251469 Board identification only (p. 17)
B-3 250466-01 252278 Service reference diagram p. 33, parts list pp. 34-35, layout p. 36, schematics p. 37
E 250469-01 252312 Service reference diagram p. 39, parts list p. 40, layout p. 41, schematic p. 42

Contents

Title Page
Specifications 1
Product parts list (case, keyboard, accessories; C64 and C64C) 2
Block diagram 3
Circuit theory: power supply, reset logic, clock circuits 4-6
Circuit theory: I/O, ROM and expansion port; RAM control logic 7-8
Circuit theory: 5-pin and 8-pin video and audio outputs 9-10
Circuit theory: cassette interface; keyboard, joystick and paddle interfaces; serial interface and user port 11-13
Troubleshooting guide 14-16
Board identification 17
PCB assembly 326298-01 18-22
PCB assembly 250407-04, with modulator schematic 251025 23-27
PCB assembly 250425-01, with modulator schematic 251696 28-32
B-3: service reference diagram, parts list, layout, schematics 252278 33-37
E: service reference diagram, parts list, layout, schematic 252312 39-42

The pin assignment pages describe the 6526 CIA and 6581 SID (p. 21), the 6510 and the 82S100 PLA (p. 27) and the 6567 VIC-II (p. 32) pin by pin.

What this manual settles

  • The B-3 and E boards. Pages 33-42 are not in the 1985 editions (Commodore 64 Service Manual (1985 Mar), Commodore 64 Service Manual (1985 Sep)), which cover 326298, 250407 and 250425 only.
  • Component values for each board, with Commodore part numbers on the B-3 and E lists. These are the source for Commodore 64 Capacitor Replacement Guide and Commodore 64C Capacitor Replacement Guide.
  • The E board's build options. Notes on schematic 252312 give the parts that change with the SID (CR7 12.6 V or 9.6 V zener; C70/C71 470 pF or 22000 pF; C80/C81 1800 pF or 2200 pF; R8 removed for the 8580), the French version (C63 2200 µF and R2 20 Ω), the NTSC/PAL jumper J3 and the crystal and dot-clock frequencies.
  • Commodore's symptom table: 37 symptoms with the parts to check, in long-board designators (pp. 14-16).

Two printing slips: the board identification table gives the B-3 assembly as "250446" where its parts list and layout say 250466, and the circuit-theory text says +5 V reaches CN7 on "pins 5 and 1" where the drawing on the same page shows pins 1-3 as ground. The C64B clock text gives Y1 as 16 MHz; the 250425 and B-3 parts lists give 14.31818 MHz.

What this manual does not contain

  • The external power supply. Only the board's own supply circuits are described.
  • A parts list or schematic for the B-2 (250441); Commodore lists its changes from the B on p. 17.
  • Disk drives and other peripherals.
  • Keyboard parts below assembly level.
  • Step-by-step measurements with expected readings; those are in Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01).

Download: Commodore 64 - 64C Service Manual.pdf (5 MB)

Other Commodore 64 service documentation

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