Commodore VIC-20 General Maintenance
The Commodore VIC-20 (a.k.a. VC-20 / VIC-1001) was the first home computer to sell more than a million units. Although far simpler than later 8-bit machines, four decades of heat, dust, and leaking components can destroy a VIC-20.
This General Maintenance Guide walks through cleaning, power-supply care, keyboard service, capacitor replacement, and other longevity tips specific to the VIC-20.
Regular Cleaning
[edit | edit source]Internal Cleaning
[edit | edit source]- Unplug the computer and disconnect the power brick, RF/modulator lead, and peripherals.
- Remove six case screws (three on top, three below) and carefully separate the halves.
- Blow loose dust away with compressed air. Pay extra attention to:
- VIC-I heat-sink fins
- Regulator heat-shield (5 V linear)
- Cartridge & user-port edges
- Brush stubborn debris off the board with a soft ESD brush.
- Spot-clean grime with >90 % isopropyl alcohol (IPA) on cotton swabs. Avoid flooding the area around the VIC-I chip — its ceramic package can wick IPA under the metal can.
Exterior / Keyboard
[edit | edit source]- Wipe the textured top shell with a damp microfiber cloth and mild soap.
- Do not soak the decal-foil badge; its adhesive weakens easily.
- Pop key-caps with a key-puller; soak in warm soapy water.
- Clean the plungers and PCB contact pads with IPA.
- For yellowed ABS, follow the Retrobrite procedure.
Power Supply & Regulator Care
[edit | edit source]The “Silver Brick” PSU
[edit | edit source]| Model | Output | Failure mode |- | 902503-03 | 5 V DC @ 1 A | Shorted capacitor → over-voltage | 902502-02 | 9 V AC @ 3 A + 5 V DC @ 1 A (two-pin) | RIFA X2 blow-out
- Measure the brick’s unloaded 5 V rail; anything above 5.20 V—retire it.
- Replace cracked RIFA X2 suppression caps (0.1 µF & 0.47 µF).
- Modern replacements: C64 “black bricks” (5 V/9 VAC) or aftermarket switch-mode PSUs.
On-Board Regulation
[edit | edit source]The 9 VAC feeds two on-board regulators:
- LM7805 – 5 V for core logic
- LM7812 (PAL) or zener dropper (NTSC) – 12 V for the VIC-I
Re-grease heat-sinks with silicon compound; ensure regulators are tight to the shield. Check electrolytics C12/C13 (5 V filter) and C48 (12 V filter) for bulging.
Capacitor Replacement (Recap)
[edit | edit source]A VIC-20 contains ~25 electrolytics; most live in a cool environment and age well, except the two next to the regulators and RF modulator.
| Board Pos. | Capacitance | Voltage | Notes |
|---|---|---|---|
| C12 | 2200 µF | 16 V | 5 V input filter – replace first |
| C13 | 470 µF | 16 V | 5 V output smoother |
| C48 | 470 µF | 35 V | 12 V rail (PAL only) |
| C88–C93 | 10 µF | 16 V | Audio/DAC bypass |
| C212 | 100 µF | 10 V | RF modulator 5 V filter |
Use low-ESR 105 °C caps (Nichicon UPW/UHW, Panasonic FR/FC).
Keyboard & Joystick Ports
[edit | edit source]Mitsumi “Full-Travel” Keyboard
[edit | edit source]- Each key uses conductive rubber plungers → loss of conductivity causes bounce or dead keys.
- Lightly buff the carbon pill with a pencil eraser, then wipe with IPA.
- Reassemble with dielectric grease on stabilizer bars to stop squeaks.
Cleaning Edge-Connectors
[edit | edit source]- Cartridge, cassette, and user ports tarnish.
- Swipe contacts with a lint-free strip soaked in DeoxIT.
- Avoid abrasion (ink erasers) — gold flash is thin.
Video / VIC-I Chip Thermal Care
[edit | edit source]| Part | Region | Supply | Remarks |
|---|---|---|---|
| 6560 | NTSC | 5 V & 12 V | Can runs hot; add stick-on heat-sink |
| 6561-101 | PAL-B | 5 V only | Slightly cooler, same pin-out |
- Keep the RF shield in place — it doubles as a heat-spreader for the VIC.
- If video shows checkerboard or jail-bars, recap the modulator (C212) and verify VIC 14 MHz crystal.
Voltage / Clock Test Points
[edit | edit source]| Test | Location (Assy 250403) | Expected |
|---|---|---|
| +5 V | Pin 1 of 6522 VIA | 5.00 ± 0.10 V |
| +12 V (PAL) | Pin 12 of 6561 | 11.8 – 12.2 V |
| φ2 CPU clock | Pin 37 of 6502 | 1.02 MHz (NTSC) / 1.11 MHz (PAL) |
| Color burst | VIC pin 17 (out) | 3.58 MHz (NTSC) / 4.433 MHz (PAL) |
Use an oscilloscope or frequency counter; jitter over ±0.01 MHz indicates crystal or cap C7 drift.
Common Faults Checks
[edit | edit source]| Symptom | Likely Cause | First Checks |
|---|---|---|
| Black screen, no border | Dead 6502 or broken 5 V | Confirm 5 V, reseat CPU |
| Black screen, white border | Bad RAM (2114 color RAM) | Piggy-back test or swap U23 |
| Random characters | Dirty cartridge port OR failing 6522 | Clean edge, swap VIA |
| No sound | Faulty 6581/6560 audio filter caps | Replace C88–C91 |
| Snow in RF | Modulator caps dried | Replace C212, C207 |
Recommended Tool Kit
[edit | edit source]- T-15 Torx & Phillips drivers
- ESD wrist-strap
- High-quality soldering station & flux pen
- Oscilloscope (≥10 MHz) or logic probe
- DeoxIT + IPA 99 %
- 250 mA slow-blow fuse (spare for PSU)
- Diagnostic cartridge (VIC-20 Dead Test, Penultimate +/Final Expansion)
Further Resources
[edit | edit source]- Commodore VIC-20 Technical Manual (314001-02) – schematics & waveforms.
- VIC-20 Field Service Test Cartridge – RAM/ROM and sound loops.
- Commodore VIC-20 Capacitor Replacement Guide
- Commodore VIC-20 Troubleshooting Guide
- CRT Discharge Procedure (for 1701/1702 monitor owners)