Commodore 64

This "breadbin" Commodore 64 (long board revision) arrived with a familiar story: the owner's childhood machine, last used in the early 1990s and stored in a loft ever since. The case was in reasonable cosmetic condition but heavily yellowed, particularly on the top lid.

On power-on, the machine displayed a completely blank screen — no blue border, no cursor, nothing. The power LED lit correctly, suggesting the 9V AC and 5V DC lines were at least partially functional. A "dead black screen" on a C64 typically points to the PLA, VIC-II, CPU, or a RAM failure.

The keyboard felt mushy and several keys were intermittent — a common result of aged foam and rubber contact pads degrading over decades.

1. Diagnosis
Using a logic analyser on the address bus and an oscilloscope on the VIC-II clock line, I confirmed the VIC-II chip itself was alive but producing no video. Tracing the issue upstream, the MOS 6567/6569 colour output pin was floating — pointing to the SID chip rather than VIC. Swapping the SID with a known-good chip confirmed the fault: the original MOS 6581 was dead.

2. SID Chip Replacement
The original MOS 6581 was desoldered using a Hakko FR-300 desoldering gun and replaced with a socket, into which a tested 6581 from my parts stock was fitted. This approach also allows easy future chip swaps. After the replacement, the machine immediately booted to the familiar blue BASIC screen.

3. Full Motherboard Recap
All electrolytic capacitors on the long board were replaced with Nichicon Fine Gold series (audio grade) caps where appropriate, and Panasonic FR series for the power filtering caps. The original C64 long board uses a total of 14 electrolytics. All were replaced preventatively.

4. Keyboard Restoration
The keyboard assembly was fully disassembled. The foam backing sheet (which had completely disintegrated, as is universal on C64 keyboards of this age) was replaced with laser-cut 3mm craft foam. Each contact pad was inspected and wiped down. All 66 keys now register correctly in a matrix test.

5. Case Retrobright & Cleaning
Both case halves and all keycaps were retrbrighted to a uniform beige. Internal RF shielding was removed, cleaned of surface oxidation, and refitted. The case was reassembled with new Torx screws where originals had stripped.

The restored C64 was run through Dead Test cartridge diagnostics — all RAM banks pass, all I/O chips respond correctly. Audio was verified through both the A/V output and the RF modulator. The three SID voices produce correct pitch and envelope response, confirmed with Rob Hubbard's "Commando" music player.

The machine was also tested with a period-correct 1541-II disk drive (separately restored), loading multiple game titles from original disks without errors. The IEC serial bus, joystick ports, and user port all test correctly.