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Created page with "{{Infobox computer | name = Commodore 64 | image = 250px | caption = Commodore 64 – The Best-Selling Home Computer | manufacturer = Commodore Business Machines | type = Home Computer | release date = August 1982 | discontinued = April 1994 | price = US$595 (1982) | cpu = MOS Technology 6510 @ 1.023 MHz (NTSC) / 0.985 MHz (PAL) | memory = 64 KB RAM, 20 KB ROM (BASIC 2.0, KERNAL, Character ROM) |..."
 
Name the two Commodore books whose content is nearest to hardware, with what each actually documents and, for Machine Language for Beginners, the extent of the missing pages in the scan
 
(13 intermediate revisions by the same user not shown)
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| name        = Commodore 64
| name        = Commodore 64
| image        = [[File:Commodore64.jpg|250px]]
| image        = [[File:Commodore64.jpg|250px]]
| caption      = Commodore 64 – The Best-Selling Home Computer
| caption      = Commodore 64 – the best-selling home computer
| manufacturer = Commodore Business Machines
| manufacturer = Commodore Business Machines
| type        = Home Computer
| type        = Home computer
| release date = August 1982
| release date = August 1982
| discontinued = April 1994
| discontinued = April 1994
| price        = US$595 (1982)
| price        = US$595 (1982)
| cpu          = MOS Technology 6510 @ 1.023 MHz (NTSC) / 0.985 MHz (PAL)
| cpu          = MOS Technology 6510 @ 1.023 MHz (NTSC) / 0.985 MHz (PAL)
| memory      = 64 KB RAM, 20 KB ROM (BASIC 2.0, KERNAL, Character ROM)
| memory      = 64 KB RAM, 20 KB ROM (BASIC 2.0, KERNAL, character generator)
| storage      = External cassette tape (Datasette), optional 5.25" floppy disk drive (1541)
| storage      = Datasette cassette recorder; 1540/1541 5.25-inch floppy drive
| display      = 320×200 pixels, 40×25 text characters, 16 colors
| display      = 320×200 pixels, 40×25 text characters, 16 colours
| sound        = SID 6581/8580: 3 voices, 4 waveforms, filters, ADSR envelope
| graphics    = MOS 6567 (NTSC) / 6569 (PAL) VIC-II, 8 hardware sprites
| sound        = MOS 6581 / 8580 SID: 3 voices, 4 waveforms, filter, ADSR
| dimensions  = 40.6 cm × 21.6 cm × 7.6 cm
| dimensions  = 40.6 cm × 21.6 cm × 7.6 cm
| weight      = 1.8 kg
| weight      = 1.8 kg
| os          = Commodore BASIC 2.0 (in ROM)
| power        = External brick: regulated +5 V DC and 9 V AC, 7-pin DIN
| os          = Commodore BASIC 2.0 in ROM
| predecessor  = [[Commodore VIC-20]]
| predecessor  = [[Commodore VIC-20]]
| successor    = [[Commodore 128]]
| successor    = [[Commodore 64C]]
| codename    = VIC-40
| codename    = VIC-40
| model        = C64, C64C, SX-64
| model        = C64, C64C, SX-64
| logo        = [[File:Commodore64 logo.svg|200px]]
| logo        = [[File:Commodore 64 logo-00.svg|250px]]
}}
}}
<templatestyles src="Template:StyledTable/styles.css" />


The '''Commodore 64''' (C64) is an 8-bit home computer introduced by Commodore Business Machines in August 1982. With its advanced graphics and sound capabilities, it became the best-selling single personal computer model of all time, with estimates ranging from 12.5 to 17 million units sold.
The '''Commodore 64''' (C64) is an 8-bit home computer introduced by Commodore Business Machines in August 1982 and sold until Commodore's collapse in April 1994. It is generally regarded as the best-selling single computer model ever made; the commonly quoted range is '''12.5 to 17 million units''', the upper figure being Commodore's own claim and the lower an estimate derived from Commodore's published financial data. No audited production total was ever released, so any single number given as fact is a choice between those two.<ref name="reimer">Jeremy Reimer, "Total share: 30 years of personal computer market share figures", Ars Technica, 14 December 2005, and the author's subsequent sales-data spreadsheet. The source of the ~12.5 million estimate, derived from Commodore's quarterly reports, against Commodore's own marketing claim of 17 million.</ref>


== 🧠 Architecture and Processor ==
'''The hardware figures on this page are taken from Commodore's own service literature''' — the ''C64 / C64C Service Manual'' and the ''Commodore 64 Technical Manual and Parts List'', both hosted here.<ref name="sm">Commodore Business Machines, ''C64 / C64C Service Manual'', March 1992, PN-314001-03, hosted at [[Commodore 64 / 64C Service Manual]]. Contains the board-identification tables, the circuit-theory sections describing the power supply, reset and clock circuits, component-level parts lists for every mainboard assembly, Commodore's symptom-to-component troubleshooting table, and schematics 252278 (B-3) and 252312 (E).</ref><ref name="tmpl">Commodore Business Machines, ''Commodore 64 Technical Manual and Parts List'', hosted at [[Commodore 64 Technical Manual and Parts List]]. Assembly-level parts lists and board drawings.</ref>
At its core, the C64 utilized the '''MOS Technology 6510''' microprocessor, a variant of the 6502 with an integrated 6-bit I/O port used for memory banking and control of the Datasette. The CPU operated at:
* '''1.023 MHz''' for NTSC systems.
* '''0.985 MHz''' for PAL systems.


The 6510's integrated I/O port allowed for dynamic switching between ROM and RAM, enabling more flexible memory management.
== Architecture and processor ==


== 💾 Memory and Storage ==
The CPU is the '''MOS Technology 6510''', a 6502 core with an on-chip 6-bit I/O port at $0000/$0001 used to bank ROM, RAM and I/O in and out of the address space and to control the Datasette motor. It runs at '''1.023 MHz''' on NTSC machines and '''0.985 MHz''' on PAL machines, both derived from the video crystal rather than from a separate CPU oscillator.<ref name="sm" />
The C64 came equipped with:
* '''64 KB RAM''', with approximately 38 KB available for BASIC programs.
* '''20 KB ROM''', comprising:
** 8 KB for Commodore BASIC 2.0.
** 8 KB for the KERNAL (operating system routines).
** 4 KB for character ROM (two 2 KB character sets).


Storage options included:
'''The 6510's +5 V supply is pin 6, not pin 40.''' Pin 40 is RESET and pin 21 is ground. This matters because probing pin 40 for a supply rail is a documented way to misdiagnose a healthy CPU, and because the 6502 in other machines is pinned differently.<ref name="sm" />
* '''Datasette''' – a cassette tape drive for loading and saving programs.
* '''1541 floppy disk drive''' – a 5.25" drive offering faster and more reliable storage.


== 🖥️ Display and Graphics ==
== Memory ==
Graphics were handled by the '''MOS Technology VIC-II''' chip, providing:
* Resolution of '''320×200 pixels'''.
* Text display of '''40 columns × 25 rows'''.
* Support for '''16 colors'''.
* Hardware sprites: '''8 sprites''' of 24×21 pixels, with collision detection.
* Smooth scrolling and raster interrupts for advanced graphical effects.


The VIC-II's capabilities allowed for detailed graphics and animations, setting the C64 apart from its contemporaries.
* '''64 KB RAM''', of which 38,911 bytes are free to BASIC.
* '''20 KB ROM''': 8 KB BASIC 2.0, 8 KB KERNAL, 4 KB character generator holding two 2 KB sets.


== 🔊 Sound Capabilities ==
Banking is done by the 6510's port lines together with the /GAME and /EXROM lines from the cartridge port, so a cartridge can replace BASIC, the KERNAL or both.
Audio was generated by the '''MOS Technology SID''' (Sound Interface Device) chip, offering:
* '''3 independent voices''' with programmable ADSR envelopes.
* '''4 waveform types''': triangle, sawtooth, pulse, and noise.
* Ring modulation and oscillator synchronization.
* Programmable filters: low-pass, high-pass, band-pass, and notch.


The SID chip's rich sound capabilities contributed to the C64's popularity in music production and gaming.
'''$C000–$CFFF is plain RAM.''' It is a 4 KB block that no ROM or I/O device overlays, which is why so much machine code lives there. It is not an I/O window, and pages that describe it as one are wrong.


== 🎮 Input/Output and Expansion ==
== Display and graphics ==
The C64 featured a variety of I/O ports:
* '''Cartridge Expansion Port''' – for software cartridges and hardware expansions.
* '''User Port''' – a versatile interface for modems, printers, and custom devices.
* '''Serial Port''' – for connecting disk drives and printers.
* '''Cassette Port''' – for the Datasette.
* '''Two Joystick Ports''' – compatible with Atari-style controllers.
* '''RF and Composite Video Outputs''' – for connection to TVs and monitors.


These ports allowed for extensive expandability, catering to both casual users and enthusiasts.
Graphics come from the '''VIC-II''' — 6567 on NTSC machines, 6569 on PAL:


== 🧰 General Maintenance ==
* 320×200 pixels, or 40 columns × 25 rows of text
Over time, Commodore 64 computers may experience issues common to vintage electronics, such as:
* 16 colours
* Aging capacitors leading to power supply instability or failure.
* 8 hardware sprites of 24×21 pixels with collision detection
* Keyboard contact wear causing unresponsive or erratic key behavior.
* Smooth scrolling and raster interrupts
* Overheating of the voltage regulators, potentially leading to component damage.
* Degradation of the RF modulator affecting video output quality.


Regular maintenance, including capacitor replacement, keyboard cleaning, and ensuring proper heat dissipation, can help preserve the functionality of these systems. For detailed procedures, refer to the [[Commodore 64 Maintenance Guide]].
== Sound ==


== 🧾 PCB Schematics & Service Guide ==
The '''SID''' (Sound Interface Device), 6581 on earlier machines and 8580 on later ones, provides three independent voices with ADSR envelopes, four waveforms (triangle, sawtooth, pulse, noise), ring modulation, oscillator sync and a multi-mode filter.
The C64 underwent several motherboard revisions, each with slight variations:
* '''Assy 326298''' – Early models with 8 RAM chips.
* '''Assy 250407''' – Common revision with improved reliability.
* '''Assy 250425''' – Featured in the C64C with consolidated chips.
* '''Assy 250466''' – Later C64C models with further integration.


=== 📷 Motherboard Images ===
'''SID audio output is pin 27.''' Pin 28 is Vdd — the 12 V supply — and pin 26 is the external audio input. Taking audio from pin 28 puts 12 V into whatever you connect, and is a mistake that appears on a number of modding guides.<ref name="sm" />
{| class="wikitable" style="width:75%; text-align:center;"
 
== Power ==
 
The C64's power comes from an external brick that supplies '''a regulated +5 V DC rail and a 9 V AC winding''' on a 7-pin DIN. Commodore's circuit theory is explicit that the 5 V from the brick feeds the logic directly — there is no second regulator on the board standing between the brick and the chips, which is why a brick that fails high takes the custom chips with it.<ref name="sm" />
 
{| class="wikitable styled-table" style="width:80%; text-align:left;"
|+'''Power connector CN7, 7-pin DIN'''
! Pin !! Function
|-
| 1, 2, 3 || Ground
|-
| 4 || Not connected on long boards; +5 V on the E board
|-
| 5 || +5 V DC, regulated, from the brick
|-
| 6, 7 || 9 V AC
|}
 
'''Pins 1 to 3 are all ground''', so measuring between pin 1 and pin 2 measures nothing. The 9 V AC also appears across '''user-port pins 10 and 11''', which is where it is normally taken from for expansions.<ref name="sm" />
 
On the board, 9 V AC is rectified and regulated to produce '''+12 V''' (VR1, an MC7812CT, feeding the VIC-II, the SID and the audio stages) and a second '''+5 V''' for the video and clock circuits (VR2, an MC7805CT), plus a '''+9 V unregulated''' rail for the cassette motor.<ref name="sm" />
 
For over-voltage protection see [[Commodore 64 Power-Supply Protector (C64 Saver)]]; for a modern replacement mainboard see [[C64 Reloaded MK2]].
 
== Input, output and expansion ==
 
* '''Cartridge expansion port''' — full address and data bus, plus /GAME and /EXROM
* '''User port''' — 6526 CIA#2 port B, plus the 9 V AC on pins 10 and 11
* '''Serial port''' — Commodore's own bus, for 1541 drives and printers
* '''Cassette port''' — Datasette
* '''Two control ports''' — Atari-style 9-pin, also used by paddles, mice and light pens
* '''RF and composite video''' — the video connector is 5-pin DIN on the original board and 8-pin on all later ones, which is the easiest way to tell an original board from a revision<ref name="sm" />
 
== Board revisions ==
 
Commodore's own identification table. The assembly number is silkscreened on the board; the case badge tells you nothing useful.<ref name="sm" />
 
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''C64 and C64C mainboard assemblies'''
! Version !! Commodore's identifying factor !! PCB assembly !! Schematic
|-
| Original || 5-pin video connector (CN5) || 326298-01 || 326106
|-
| A (CR) || 8-pin video connector || 250407-01 || 251138
|-
| B || 8-pin connector, reduced oscillator circuit || 250425 || 251469
|-
| B-2 || Reduced oscillator with component changes || 250441-01 || 251469
|-
| B-3 || Only two RAM chips, U9 and U10 || 250466-01 || 252278
|-
| E || BASIC and KERNAL combined into U4, new memory controller at U8 || 250469-01 || 252312
|}
 
'''250425 is a long board, not a C64C board.''' The two assemblies Commodore lists under C64C identification are the '''B-3 (250466-01)''' and the '''E (250469-01)''' — see [[Commodore 64C]].<ref name="sm" />
 
On the B-2, Commodore records that resistors R28, R29, R30, R36 and R48 were replaced by resistor pack RP5, and that diodes CR100–CR105 are no longer piggybacked but fitted at CR9 and CR12–CR16.<ref name="sm" />
 
=== Motherboard and schematic ===
{| class="wikitable styled-table" style="width:75%; text-align:center;"
|-
|-
! Logic Board !! Schematic Diagrams
! Logic board !! Schematic diagrams
|-
|-
| [[File:C64 Logic Board.jpg|thumb|center|350px|Commodore 64 Logic Board]]
| [[File:C64 Logic Board.jpg|thumb|center|350px|Commodore 64 logic board]]
| [[File:C64 Schematic.png|thumb|center|350px|C64 Logic Board Schematic]]
| [[File:C64 Schematic Page 1.png|center|thumb|350x350px|C64 logic board schematic, page 1]][[File:C64 Schematic Page 2.png|center|thumb|352x352px|C64 logic board schematic, page 2]]
|}
|}


== 📚 Technical Documentation ==
== Maintenance ==
For detailed technical information, refer to the following resources:
 
* [[Commodore 64 Technical Manual]]
Failure modes worth knowing before opening one:
* [[Commodore 64 Programmer's Reference Guide]]
 
* [[Commodore 64 User Manual]]
* '''The power supply.''' Potted in epoxy, not serviceable, and it gives no warning before it fails high. This is the single most destructive fault on the machine.
* '''Keyboard contacts.''' Carbon pads and a Mylar membrane, both of which wear.
* '''The regulators and the bridge rectifier.''' VR1, VR2 and CR4 are heavy-current, thermally cycled joints; a cracked one produces an intermittent that mimics a failing chip.
* '''The RF modulator.''' Degrades and is often bypassed rather than repaired.
 
For procedures see [[Commodore 64 General Maintenance]], [[Commodore 64 Troubleshooting Guide]] and [[Commodore 64 Capacitor Replacement Guide]].
 
== Documentation hosted here ==


== 📷 Gallery ==
=== Commodore's own ===
 
{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Document !! What it is good for
|-
| '''[[Commodore 64 / 64C Service Manual]]''' || March 1992, PN-314001-03, 57 pp. The primary reference. Board identification, circuit theory, Commodore's own troubleshooting table, and component-level parts lists for '''all five''' mainboard assemblies. The only document here with the B-3 (250466) and E (250469) boards and schematics 252278 and 252312
|-
| '''[[Commodore 64 Technical Manual and Parts List]]''' || P/N 990439, 22 pp. The drawing package: drawing tree 326101, the seven-sheet parts list for assembly '''250407 rev B''', and schematic '''251138 rev A'''. An independent Commodore source for the 250407 values
|-
| '''[[Commodore 64 Service Manual (1985 Mar)]]''' and '''[[Commodore 64 Service Manual (1985 Sep)]]''' || Both PN-314001-02. The three early assemblies 326298-01, 250407-04 and 250425-01, with schematics 326106, 251138 and 251469. [[Commodore 64 Service Manual (1985 Feb)]] holds the same file as the March page &mdash; there is no February document here
|-
| '''[[Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01)]]''' || Commodore's dealer diagnostic kit. Seventeen named tests, and an explicit warning that the control port test can report a false failure
|-
| '''[[Commodore 64GS Technical Data (400401-01, 1990 May)]]''' || The Commodore 64 Games System. Assembly level only &mdash; no schematic and no component parts list. Its own cover is dated '''November 1990''', not May
|-
| '''[[Commodore Test Cartridge Index]]''' || The diagnostic cartridges themselves
|}
 
=== Third-party books ===
 
Sixty-nine third-party Commodore books are hosted on this wiki; [[:Category:Commodore Books]] is the annotated index. Almost all are programming or games books with no hardware content at all, and none should be cited for a component value. '''Four of them do reach the hardware''':
 
* '''[[Troubleshooting and Repairing your Commodore 64]]''' &mdash; Art Margolis, TAB Books, 1985, 377 pp. Twenty-one test point charts and a master schematic in the appendix.
* '''[[Commodore 64 Troubleshooting and Repair Guide]]''' &mdash; Robert C. Brenner, Sams, 1985, 183 pp. Symptom-first diagnosis, a power supply chapter and a chapter on testing capacitors.
* '''[[The Commodore 64 Kernal and Hardware Revealed]]''' &mdash; Nick Hampshire, Collins, 1985, 213 pp. Reproduces Commodore's own schematic by permission, and traces the cassette motor supply and its output waveforms.
* '''[[The Anatomy of a Commodore 64]]''' &mdash; Data Becker / First Publishing, 309 pp. Chip level rather than board level: the 6510 and the 6526 in detail and a full ROM listing, but no schematic and no parts list in this edition.
 
All four are secondary sources. Where any of them disagrees with Commodore's service manual or technical manual, those are primary. '''No figure on this page has been taken from any of them.'''
 
Two more are worth naming for what they are:
 
* '''[[DIY Robotics and Sensors]]''' &mdash; John Billingsley, Sunshine Books, 1984, 141 pp. The only book in the collection that is about '''electronics''' rather than software, and it documents the '''user port and the analogue port from the outside''' &mdash; signal levels, data direction registers, address decoding, and analogue output from CB2 on the PET. It contains no Commodore schematic and no component value for any Commodore board; its circuits are the author's own designs for things to plug in.
* '''[[Machine Language for Beginners]]''' &mdash; Richard Mansfield, COMPUTE! Publications. Its Appendix B holds the '''Commodore 64 memory map''', but '''the scan hosted here is missing about 117 of its 350 printed pages''', including the PET/CBM and VIC maps and the PET 4.0 ROM routine list. The gaps are documented on that page.
 
== Gallery ==
<gallery mode="packed" heights="200">
<gallery mode="packed" heights="200">
File:Commodore64 Front.jpg|Front view of the Commodore 64
File:Commodore-64-Computer-FL.jpg|Front view of the Commodore 64
File:Commodore64 Rear.jpg|Rear panel showing I/O ports
File:Commodore-64-Computer-BL.jpg|Rear panel showing the I/O ports
File:C64_Logic_Board.jpg|Internal motherboard layout
File:Commodore 1530 Datasette C64.jpg|Commodore 1530 Datasette
File:Commodore64 Datasette.jpg|Datasette cassette tape drive
File:C64 Logic Board.jpg|Internal motherboard layout
</gallery>
</gallery>


== 🧪 Related Pages ==
== Related pages ==
* [[Commodore 64 Maintenance Guide]]
* [[Commodore 64C]]
* [[Commodore VIC-20]]
* [[Commodore 64 General Maintenance]]
* [[Commodore 64 Troubleshooting Guide]]
* [[Commodore 64 Troubleshooting Guide]]
* [[Commodore 64 Keyboard Repair Guide]]
* [[Commodore 64 Capacitor Replacement Guide]]
* [[Commodore 64 Capacitor Replacement Guide]]
* [[Commodore 64 Power-Supply Protector (C64 Saver)]]
* [[C64 Reloaded MK2]]
== References ==
<references />


[[Category:Commodore Systems]]
[[Category:Commodore Systems]]

Latest revision as of 02:32, 25 September 2026

Commodore 64
Commodore 64 – the best-selling home computer
Specifications
ManufacturerCommodore Business Machines
TypeHome computer
ReleasedAugust 1982
DiscontinuedApril 1994
Intro priceUS$595 (1982)
CPUMOS Technology 6510 @ 1.023 MHz (NTSC) / 0.985 MHz (PAL)
Memory64 KB RAM, 20 KB ROM (BASIC 2.0, KERNAL, character generator)
StorageDatasette cassette recorder; 1540/1541 5.25-inch floppy drive
Display320×200 pixels, 40×25 text characters, 16 colours
SoundMOS 6581 / 8580 SID: 3 voices, 4 waveforms, filter, ADSR
GraphicsMOS 6567 (NTSC) / 6569 (PAL) VIC-II, 8 hardware sprites
PowerExternal brick: regulated +5 V DC and 9 V AC, 7-pin DIN
Dimensions40.6 cm × 21.6 cm × 7.6 cm
Weight1.8 kg
OS / FirmwareCommodore BASIC 2.0 in ROM
PredecessorCommodore VIC-20
SuccessorCommodore 64C
CodenameVIC-40
Model no.C64, C64C, SX-64

The Commodore 64 (C64) is an 8-bit home computer introduced by Commodore Business Machines in August 1982 and sold until Commodore's collapse in April 1994. It is generally regarded as the best-selling single computer model ever made; the commonly quoted range is 12.5 to 17 million units, the upper figure being Commodore's own claim and the lower an estimate derived from Commodore's published financial data. No audited production total was ever released, so any single number given as fact is a choice between those two.[1]

The hardware figures on this page are taken from Commodore's own service literature — the C64 / C64C Service Manual and the Commodore 64 Technical Manual and Parts List, both hosted here.[2][3]

Architecture and processor

[edit | edit source]

The CPU is the MOS Technology 6510, a 6502 core with an on-chip 6-bit I/O port at $0000/$0001 used to bank ROM, RAM and I/O in and out of the address space and to control the Datasette motor. It runs at 1.023 MHz on NTSC machines and 0.985 MHz on PAL machines, both derived from the video crystal rather than from a separate CPU oscillator.[2]

The 6510's +5 V supply is pin 6, not pin 40. Pin 40 is RESET and pin 21 is ground. This matters because probing pin 40 for a supply rail is a documented way to misdiagnose a healthy CPU, and because the 6502 in other machines is pinned differently.[2]

Memory

[edit | edit source]
  • 64 KB RAM, of which 38,911 bytes are free to BASIC.
  • 20 KB ROM: 8 KB BASIC 2.0, 8 KB KERNAL, 4 KB character generator holding two 2 KB sets.

Banking is done by the 6510's port lines together with the /GAME and /EXROM lines from the cartridge port, so a cartridge can replace BASIC, the KERNAL or both.

$C000–$CFFF is plain RAM. It is a 4 KB block that no ROM or I/O device overlays, which is why so much machine code lives there. It is not an I/O window, and pages that describe it as one are wrong.

Display and graphics

[edit | edit source]

Graphics come from the VIC-II — 6567 on NTSC machines, 6569 on PAL:

  • 320×200 pixels, or 40 columns × 25 rows of text
  • 16 colours
  • 8 hardware sprites of 24×21 pixels with collision detection
  • Smooth scrolling and raster interrupts

Sound

[edit | edit source]

The SID (Sound Interface Device), 6581 on earlier machines and 8580 on later ones, provides three independent voices with ADSR envelopes, four waveforms (triangle, sawtooth, pulse, noise), ring modulation, oscillator sync and a multi-mode filter.

SID audio output is pin 27. Pin 28 is Vdd — the 12 V supply — and pin 26 is the external audio input. Taking audio from pin 28 puts 12 V into whatever you connect, and is a mistake that appears on a number of modding guides.[2]

Power

[edit | edit source]

The C64's power comes from an external brick that supplies a regulated +5 V DC rail and a 9 V AC winding on a 7-pin DIN. Commodore's circuit theory is explicit that the 5 V from the brick feeds the logic directly — there is no second regulator on the board standing between the brick and the chips, which is why a brick that fails high takes the custom chips with it.[2]

Power connector CN7, 7-pin DIN
Pin Function
1, 2, 3 Ground
4 Not connected on long boards; +5 V on the E board
5 +5 V DC, regulated, from the brick
6, 7 9 V AC

Pins 1 to 3 are all ground, so measuring between pin 1 and pin 2 measures nothing. The 9 V AC also appears across user-port pins 10 and 11, which is where it is normally taken from for expansions.[2]

On the board, 9 V AC is rectified and regulated to produce +12 V (VR1, an MC7812CT, feeding the VIC-II, the SID and the audio stages) and a second +5 V for the video and clock circuits (VR2, an MC7805CT), plus a +9 V unregulated rail for the cassette motor.[2]

For over-voltage protection see Commodore 64 Power-Supply Protector (C64 Saver); for a modern replacement mainboard see C64 Reloaded MK2.

Input, output and expansion

[edit | edit source]
  • Cartridge expansion port — full address and data bus, plus /GAME and /EXROM
  • User port — 6526 CIA#2 port B, plus the 9 V AC on pins 10 and 11
  • Serial port — Commodore's own bus, for 1541 drives and printers
  • Cassette port — Datasette
  • Two control ports — Atari-style 9-pin, also used by paddles, mice and light pens
  • RF and composite video — the video connector is 5-pin DIN on the original board and 8-pin on all later ones, which is the easiest way to tell an original board from a revision[2]

Board revisions

[edit | edit source]

Commodore's own identification table. The assembly number is silkscreened on the board; the case badge tells you nothing useful.[2]

C64 and C64C mainboard assemblies
Version Commodore's identifying factor PCB assembly Schematic
Original 5-pin video connector (CN5) 326298-01 326106
A (CR) 8-pin video connector 250407-01 251138
B 8-pin connector, reduced oscillator circuit 250425 251469
B-2 Reduced oscillator with component changes 250441-01 251469
B-3 Only two RAM chips, U9 and U10 250466-01 252278
E BASIC and KERNAL combined into U4, new memory controller at U8 250469-01 252312

250425 is a long board, not a C64C board. The two assemblies Commodore lists under C64C identification are the B-3 (250466-01) and the E (250469-01) — see Commodore 64C.[2]

On the B-2, Commodore records that resistors R28, R29, R30, R36 and R48 were replaced by resistor pack RP5, and that diodes CR100–CR105 are no longer piggybacked but fitted at CR9 and CR12–CR16.[2]

Motherboard and schematic

[edit | edit source]
Logic board Schematic diagrams
Commodore 64 logic board
C64 logic board schematic, page 1
C64 logic board schematic, page 2

Maintenance

[edit | edit source]

Failure modes worth knowing before opening one:

  • The power supply. Potted in epoxy, not serviceable, and it gives no warning before it fails high. This is the single most destructive fault on the machine.
  • Keyboard contacts. Carbon pads and a Mylar membrane, both of which wear.
  • The regulators and the bridge rectifier. VR1, VR2 and CR4 are heavy-current, thermally cycled joints; a cracked one produces an intermittent that mimics a failing chip.
  • The RF modulator. Degrades and is often bypassed rather than repaired.

For procedures see Commodore 64 General Maintenance, Commodore 64 Troubleshooting Guide and Commodore 64 Capacitor Replacement Guide.

Documentation hosted here

[edit | edit source]

Commodore's own

[edit | edit source]
Document What it is good for
Commodore 64 / 64C Service Manual March 1992, PN-314001-03, 57 pp. The primary reference. Board identification, circuit theory, Commodore's own troubleshooting table, and component-level parts lists for all five mainboard assemblies. The only document here with the B-3 (250466) and E (250469) boards and schematics 252278 and 252312
Commodore 64 Technical Manual and Parts List P/N 990439, 22 pp. The drawing package: drawing tree 326101, the seven-sheet parts list for assembly 250407 rev B, and schematic 251138 rev A. An independent Commodore source for the 250407 values
Commodore 64 Service Manual (1985 Mar) and Commodore 64 Service Manual (1985 Sep) Both PN-314001-02. The three early assemblies 326298-01, 250407-04 and 250425-01, with schematics 326106, 251138 and 251469. Commodore 64 Service Manual (1985 Feb) holds the same file as the March page — there is no February document here
Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01) Commodore's dealer diagnostic kit. Seventeen named tests, and an explicit warning that the control port test can report a false failure
Commodore 64GS Technical Data (400401-01, 1990 May) The Commodore 64 Games System. Assembly level only — no schematic and no component parts list. Its own cover is dated November 1990, not May
Commodore Test Cartridge Index The diagnostic cartridges themselves

Third-party books

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Sixty-nine third-party Commodore books are hosted on this wiki; Category:Commodore Books is the annotated index. Almost all are programming or games books with no hardware content at all, and none should be cited for a component value. Four of them do reach the hardware:

All four are secondary sources. Where any of them disagrees with Commodore's service manual or technical manual, those are primary. No figure on this page has been taken from any of them.

Two more are worth naming for what they are:

  • DIY Robotics and Sensors — John Billingsley, Sunshine Books, 1984, 141 pp. The only book in the collection that is about electronics rather than software, and it documents the user port and the analogue port from the outside — signal levels, data direction registers, address decoding, and analogue output from CB2 on the PET. It contains no Commodore schematic and no component value for any Commodore board; its circuits are the author's own designs for things to plug in.
  • Machine Language for Beginners — Richard Mansfield, COMPUTE! Publications. Its Appendix B holds the Commodore 64 memory map, but the scan hosted here is missing about 117 of its 350 printed pages, including the PET/CBM and VIC maps and the PET 4.0 ROM routine list. The gaps are documented on that page.
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  • Front view of the Commodore 64
    Front view of the Commodore 64
  • Rear panel showing the I/O ports
    Rear panel showing the I/O ports
  • Commodore 1530 Datasette
    Commodore 1530 Datasette
  • Internal motherboard layout
    Internal motherboard layout
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References

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  1. ↑ Jeremy Reimer, "Total share: 30 years of personal computer market share figures", Ars Technica, 14 December 2005, and the author's subsequent sales-data spreadsheet. The source of the ~12.5 million estimate, derived from Commodore's quarterly reports, against Commodore's own marketing claim of 17 million.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 Commodore Business Machines, C64 / C64C Service Manual, March 1992, PN-314001-03, hosted at Commodore 64 / 64C Service Manual. Contains the board-identification tables, the circuit-theory sections describing the power supply, reset and clock circuits, component-level parts lists for every mainboard assembly, Commodore's symptom-to-component troubleshooting table, and schematics 252278 (B-3) and 252312 (E).
  3. ↑ Commodore Business Machines, Commodore 64 Technical Manual and Parts List, hosted at Commodore 64 Technical Manual and Parts List. Assembly-level parts lists and board drawings.
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