Editing Commodore VIC-20 General Maintenance

[[File:VIC20_Logic_Board.jpg|thumb|450px|Commodore VIC-20 motherboard (Assy 250403, 1982).]]

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 ==

=== Internal Cleaning ===
# '''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 ===
* 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 ==

=== The “Silver Brick” PSU ===
| 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 ===
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) ==

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.

{| class="wikitable styled-table" style="width:70%; text-align:center;"
! 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 ==

=== Mitsumi “Full-Travel” Keyboard ===
* 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 ===
* 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 ==

{| class="wikitable" style="width:60%; text-align:center;"
|+'''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 ==

{| class="wikitable styled-table" style="width:65%; text-align:center;"
! 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 ==
{| class="wikitable styled-table" style="width:100%;"
! 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 ==
* 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 ==
* '''[[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)

[[Category:Commodore Systems]]
[[Category:Maintenance Guides]]