RetroTechCollection

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.

Commodore VIC-20 motherboard (Assy 250403, 1982).

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

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Internal Cleaning

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  1. Unplug the computer and disconnect the power brick, RF/modulator lead, and peripherals.
  2. Remove six case screws (three on top, three below) and carefully separate the halves.
  3. 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
  1. Brush stubborn debris off the board with a soft ESD brush.
  2. 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

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  • 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

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The “Silver Brick” PSU

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| 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

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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)

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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

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Mitsumi “Full-Travel” Keyboard

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  • 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

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  • 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

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VIC-I Variants
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

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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

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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
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  • 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

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