Commodore 64 Machine Hub
Board reference, diagnostics, IC pinouts and repair resources — everything you need on the workbench when servicing a C64.
Motherboard ASSY Selector
Select your board revision to view the electrolytic capacitor list and IC layout.
ASSY 250407 Rev A & B — 1982–83
The original "longboard" motherboard found in early breadbin C64s. Uses discrete 4116 DRAM (16×1-bit, 8 chips), a 5-pin DIN A/V connector, and the original 82S100 PLA. Requires all three voltage rails from the PSU: +5 V DC, +12 V DC, and 9 V AC.
Key ICs
- CPU: MOS 6510
- VIC-II: MOS 6567 (NTSC) / 6569 (PAL)
- SID: MOS 6581
- CIA ×2: MOS 6526
- PLA: 82S100 / 906114-01
- DRAM: 8× 4116 (16K×1)
- Colour RAM: 2114 (1K×4 SRAM)
Electrolytic Capacitor List
| Ref | Value | Voltage | Notes |
|---|---|---|---|
| C1 | 100 µF | 10 V | Main filter |
| C2 | 100 µF | 10 V | Main filter |
| C31 | 100 µF | 25 V | 12 V rail filter |
| C36 | 1000 µF | 10 V | 5 V bulk |
| C48 | 22 µF | 25 V | VIC-II filter |
| C88 | 10 µF | 16 V | SID filter |
| C91 | 470 µF | 16 V | Audio decoupling |
| C95 | 10 µF | 16 V | Cassette port |
| C105 | 220 µF | 10 V | RF modulator |
Replace with 105 °C low-ESR electrolytics. Consider adding extra ceramic bypass caps near the DRAM bank.
ASSY 250425 Rev A — 1983–84
Revised longboard commonly found in later breadbin cases. Replaces the 4116 DRAM with 4164 (64K×1) chips, removing the +12 V requirement for memory. Still uses the 5-pin DIN video connector and 82S100 PLA.
Key ICs
- CPU: MOS 6510
- VIC-II: MOS 6567 / 6569
- SID: MOS 6581
- CIA ×2: MOS 6526
- PLA: 82S100 / 906114-01
- DRAM: 8× 4164 (64K×1)
- Colour RAM: 2114 (1K×4 SRAM)
Electrolytic Capacitor List
| Ref | Value | Voltage | Notes |
|---|---|---|---|
| C1 | 100 µF | 10 V | Main filter |
| C2 | 100 µF | 10 V | Main filter |
| C36 | 1000 µF | 10 V | 5 V bulk |
| C48 | 22 µF | 25 V | VIC-II filter |
| C88 | 10 µF | 16 V | SID filter |
| C91 | 470 µF | 16 V | Audio decoupling |
| C95 | 10 µF | 16 V | Cassette port |
| C105 | 220 µF | 10 V | RF modulator |
No +12 V rail electrolytics needed (4164 DRAM is +5 V only). Recap all remaining electrolytics with low-ESR 105 °C parts.
ASSY 250466 Rev A & B — 1984–86
The "shortboard" redesign introduced with the C64C case. Significantly fewer components, improved layout, and an 8-pin DIN A/V connector with separate S-Video luma/chroma lines. Often paired with the 8580 SID.
Key ICs
- CPU: MOS 8500 (HMOS-II 6510)
- VIC-II: MOS 8562 (NTSC) / 8565 (PAL)
- SID: MOS 8580 (some early boards: 6581)
- CIA ×2: MOS 6526A
- PLA: 906114-01 / C64 PLA replacement
- DRAM: 2× 4464 (64K×4)
Electrolytic Capacitor List
| Ref | Value | Voltage | Notes |
|---|---|---|---|
| C1 | 100 µF | 10 V | Main filter |
| C7 | 1 µF | 50 V | Audio coupling |
| C40 | 470 µF | 16 V | Audio decoupling |
| C41 | 22 µF | 25 V | VIC-II filter |
| C81 | 10 µF | 16 V | SID filter |
| C107 | 220 µF | 10 V | RF modulator |
Fewer electrolytics than the longboard. Still recap all with 105 °C low-ESR parts. If upgrading the SID from 6581 to 8580, check the audio filter cap values.
ASSY 250469 Rev 3 & 4 — 1986–94
Final shortboard revision with the most cost-reduced design. Some late runs use the CSG-branded 8500R1 CPU. This board is the most commonly found in surviving C64C units. Uses 8-pin DIN A/V with S-Video support.
Key ICs
- CPU: CSG 8500
- VIC-II: CSG 8562 / 8565
- SID: CSG 8580
- CIA ×2: CSG 6526A
- PLA: 252535-01 (EPLA)
- DRAM: 2× 4464 (64K×4)
Electrolytic Capacitor List
| Ref | Value | Voltage | Notes |
|---|---|---|---|
| C1 | 100 µF | 10 V | Main filter |
| C7 | 1 µF | 50 V | Audio coupling |
| C40 | 470 µF | 16 V | Audio decoupling |
| C41 | 22 µF | 25 V | VIC-II filter |
| C81 | 10 µF | 16 V | SID filter |
| C107 | 220 µF | 10 V | RF modulator |
Identical cap list to the 250466. Late-production boards may have slightly different reference designators — always verify against the silkscreen.
Original PSU Danger Warning
The Commodore 64 power supply (C64 PSU, part 251053-02) is a known failure point that can destroy your machine. When the internal 5 V regulator fails, it often fails short, sending unregulated voltage (7–9 V DC) directly into the C64, killing the CPU, SID, CIAs, and potentially the VIC-II.
DIN 7-Pin Power Connector Pinout
| Pin | Signal | Spec |
|---|---|---|
| 1 | GND | Ground |
| 2 | GND | Ground |
| 3 | +5 V DC | Regulated, 1.5 A max |
| 4 | +5 V DC | Regulated, 1.5 A max (ganged with pin 3) |
| 5 | 9 V AC | ~1 A (for TOD clock & user port) |
| 6 | 9 V AC | Return |
| 7 | +5 V DC | Sense (some boards) |
Modern Replacement Options
Tip: Always measure the 5 V DC rail with a multimeter before powering on a C64 with an untested PSU. If it reads above 5.4 V, do NOT connect it.
Common Fault Checklist
Quick diagnostic reference for the most frequent Commodore 64 failures.
Black Screen (No Border)
Power LED on, but display is completely black — no border colour, no cursor.
Diagnostic Steps
- Verify PSU voltages: +5 V DC and 9 V AC present at the power connector.
- Check the CPU (6510) — remove from socket and verify the ∅2 clock is running (~1 MHz on pin 1). No clock = bad VIC-II or crystal.
- Check the PLA (82S100) — the most common single point of failure. Swap with known-good or use a PLA replacement (e.g., PLAnkton, SuperPLA).
- Test DRAM: swap individual 4116/4164 chips or use a dead-test cartridge.
- Check the ROMs: BASIC (901226-01) and KERNAL (901227-03). Verify CS and data lines.
Garbled Video / Wrong Colours
Border visible but screen shows random characters, colour bleeding, or wrong colour palette.
Diagnostic Steps
- Border present = CPU & PLA working. Focus on video path and RAM.
- Colour RAM (2114 SRAM) — wrong or missing colours indicate colour RAM failure. Check U6.
- DRAM failures often show repeated characters or "checker" patterns — use a dead-test cartridge to identify the faulty chip.
- VIC-II failure can cause distorted or missing video output. Check for hot VIC-II chip.
- Character ROM (901225-01) failure causes garbage characters with correct colours.
PLA Failure
Black screen, flashing screen, random crashes, or the machine runs hot with no display.
Diagnostic Steps
- Touch the PLA chip (U17) — if it is extremely hot to touch, it is likely failing or already dead.
- The original 82S100 / 906114-01 PLA is the single most failure-prone chip in the C64 due to heat stress.
- Swap with a known-good PLA or install a modern replacement: PLAnkton, SuperPLA, or CPLD-based alternatives.
- A dead PLA will prevent the CPU from accessing ROM and RAM — resulting in a completely dead machine.
- Modern replacements run much cooler and are highly recommended even as a preventative upgrade.
Dead SID (No Audio)
Machine boots normally with video output, but produces no sound through the A/V port or RF output.
Diagnostic Steps
- Test audio output with a known working cable and monitor/TV.
- Check the audio coupling capacitor on the A/V port output path.
- Run a SID test program (e.g., SID Tester by Matthias) to exercise all three voices.
- SID chip (6581 / 8580) is sensitive to static discharge and overvoltage. Inspect for cracks or burns.
- Replacements: original pull, ARMSID, SwinSID, FPGASID. Note: 6581 and 8580 have different filter capacitor requirements — do not swap without changing the filter caps.
C64 IC Pinouts
Direct links to full pinout reference pages for every major IC in the Commodore 64.
MOS 6510
CPU — 8-bit processor with built-in I/O port. The heart of the C64.
View Pinout →MOS 6581 SID
Sound Interface Device — 3-voice synthesiser with multi-mode filter. Longboard version.
View Pinout →MOS 8580 SID
Revised SID for shortboard C64C. Different filter characteristics and lower voltage.
View Pinout →MOS 6567/6569 VIC-II
Video Interface Chip — generates all video output, sprites, and handles DRAM refresh.
View Pinout →MOS 6526 CIA
Complex Interface Adapter — keyboard scanning, joystick ports, serial bus, and TOD clock.
View Pinout →82S100 PLA
Programmable Logic Array — memory map decoding and bank switching. #1 failure point.
View Pinout →4116 DRAM
16K×1 dynamic RAM — used in early longboard C64s. Needs ±5 V and +12 V.
View Pinout →4164 DRAM
64K×1 dynamic RAM — replaced 4116 in later breadbin boards. +5 V only.
View Pinout →A/V & Serial Port Pinouts
Reference pinouts for the C64 audio/video and IEC serial bus connectors.
8-Pin DIN A/V Port C64C / Shortboard
Found on ASSY 250466 and 250469 boards. Supports S-Video (separate luma/chroma) and composite.
| Pin | Signal | Notes |
|---|---|---|
| 1 | Luminance (Y) | S-Video luma output |
| 2 | GND | Signal ground |
| 3 | Audio Out | Line-level mono audio |
| 4 | Composite Video | Combined luma + chroma (CVBS) |
| 5 | Audio In | Directly connected to SID ext-in |
| 6 | Chrominance (C) | S-Video chroma output |
| 7 | +5 V DC | ~50 mA max (directly from main rail) |
| 8 | GND | Shield / ground |
Tip: For best picture quality, use pins 1 (luma) and 6 (chroma) with an S-Video cable. Composite (pin 4) combines both signals and introduces dot crawl.
5-Pin DIN A/V Port Breadbin / Longboard
Found on ASSY 250407 and 250425 boards. Composite and audio only — no native S-Video breakout.
| Pin | Signal | Notes |
|---|---|---|
| 1 | Luminance (Y) | Luma only (not true S-Video on most boards) |
| 2 | GND | Signal ground |
| 3 | Audio Out | Line-level mono audio |
| 4 | Composite Video | Combined CVBS signal |
| 5 | Audio In | SID external audio input |
The 5-pin DIN can be modded for S-Video by tapping the chroma signal directly from the VIC-II and adding a 6th wire. Many "S-Video mod" guides exist for the longboard.
IEC Serial Bus Port DIN 6-Pin
The C64's serial bus for disk drives (1541, 1571), printers (MPS-801), and other peripherals. Active-low, active-low open-drain protocol.
| Pin | Signal | Notes |
|---|---|---|
| 1 | /SRQ IN | Service Request (active-low) |
| 2 | GND | Signal ground |
| 3 | ATN OUT | Attention (directly from CIA#1 PA3) |
| 4 | CLK | Serial clock (active-low, open-drain) |
| 5 | DATA | Serial data (active-low, open-drain) |
| 6 | /RESET | Active-low system reset (directly from reset line) |
Use shielded cable for IEC connections over 1 m. The serial bus speed is ~400 bytes/sec stock; fast loaders bypass this via CIA timing tricks.
Resources & Further Reading
Blog posts, external references, and community links for Commodore 64 repair and restoration.
Smiggy's C64 Blog Posts
Bench Tools
- IC Pinout Finder — search all C64 & retro ICs
- Recap Planner — capacitor replacement guide
- Ohm's Law Calculator
- Capacitor Code Decoder
External Resources
- C64-Wiki — comprehensive Commodore 64 encyclopaedia
- Lemon64 Forums — active C64 community and game database
- CSDb — C64 Scene Database (demos, tools, music)
- Ray Carlsen's Pages — PSU builds and repair guides