Commodore VIC-20 Capacitor Replacement Guide
Replacing electrolytic capacitors (“recapping”) in a Commodore VIC-20 is one of the highest-impact reliability upgrades you can perform. A fresh capacitor set restores clean DC rails, reduces video noise, cures random resets, and protects rare MOS chips from over-ripple voltage spikes.
Visual Inspection & Failure Signs
[edit | edit source]- Bulging tops – Any domed aluminium case is a near-certain failure.
- Electrolyte residue – Brown crust or oily film at the capacitor base.
- ESR drift – Even if a cap looks fine, elevated ESR (> 2 Ω on small signal caps, > 0.2 Ω on main filters) is enough to destabilise the 5 V rail.
- Heat-darkened PCB – Large cans (C11/C13) often cook the FR-4 underneath; that heat ages surrounding parts as well.
If any of the above are present – or if the machine is 40 years old and un-serviced – replace the full set.
VIC-20 Logic-Board Capacitor Lists (by Assy #)
[edit | edit source]The VIC-20 has a single logic board the tables below contain all the replaceable capacitors.
Early 2-Prong Board (Assy 324003 & “214003”)
[edit | edit source]| Board Ref | Capacitance | Voltage | Purpose (rail / circuit) |
|---|---|---|---|
| C10 | 100 µF | 16 V | 9 VAC ► +5 V pre-reg filter |
| C11 | 4 700 µF | 10 V | Main +5 V bulk filter |
| C12 | 220 µF | 25 V | +12 V line for VIC analogue core |
| C13 | 1 000 µF | 16 V | Secondary +5 V smoothing (regulator out) |
| C18 | 10 µF | 16 V | Power-on reset RC timer |
| C90 | 3.3 µF | 50 V | Audio-path coupling (VIC DAC) |
| C91 | 470 µF | 10 V | Datasette motor supply filter |
Values mirror Commodore service-manual BOM; some very early 1981 PCBs mark C10/C12 as 35 V parts – 25 V or 35 V replacements are both acceptable.
Cost-Reduced “VIC-20 CR” Board (Assy 250403)
[edit | edit source]| Typical Ref | Capacitance | Voltage | Notes |
|---|---|---|---|
| C1 | 22 µF | 25 V | Reset / audio decouple (moved by layout change) |
| C2 | 10 µF | 50 V | Cassette sense filter |
| C4 | 1 000 µF | 16 V | Bulk +5 V – external PSU now supplies DC directly |
| C6 | 470 µF | 10 V | 9 VAC► +12 V doubler filter (VIC & cassette motor) |
| C7 | 100 µF | 16 V | VIC chroma/luma decouple (near RF modulator) |
| C8 | 220 µF | 25 V | +12 V rail post-rectifier filter |
> Board markings vary. Commodore deleted the on-board 7805 on Assy 250403, so the 4 700 µF can is absent; the largest can you will see is 1 000 µF. Always cross-check against your board silkscreen before ordering.
Recapping Procedure
[edit | edit source]- Disassemble – Remove six case screws, slide keyboard forward, lift the RF shield.
- Label cables – Photos help when reconnecting the power-LED & keyboard flex.
- Desolder caps cleanly using a temperature-controlled iron & braid / pump; apply gentle upward pressure only after all solder is molten to avoid lifting pads (VIC-20 traces are thin).
- Install new capacitors – observe polarity: the striped/- side to ground. Lead-spacing on main filters is 5 mm; modern 8 mm diameter caps fit without bending.
- Inspect & wash – Flux residue is mildly conductive; scrub with 99 % IPA and a soft brush.
- Re-form (optional) – Bring the board up on a bench supply through a 1 Ω resistor for the first 30 s to reform large cans gently.
Post-Recap Voltage Checks
[edit | edit source]| Test Point | Early 324003 | CR 250403 | Notes |
|---|---|---|---|
| +5 V (6502 pin 40) | 4.95 – 5.10 V | 4.95 – 5.10 V | Regulator (early) vs external PSU |
| +12 V (VIC pin 28) | 11.6 – 12.6 V | 11.6 – 12.6 V | Derived from 9 VAC doubler |
| 9 VAC (cassette port pin 4) | 8.5 – 10.0 V AC | same | Drives tape motor & 12 V doubler |
An oscilloscope should show < 50 mV p-p ripple on +5 V after recap.
Recommended Tools & Parts
[edit | edit source]- 60 W temperature-controlled iron (fine conical tip)
- Desolder‐pump and braid – VIC pads lift easily if overheated.
- ESR-meter (handy to confirm big cans).
- Leaded 63/37 Sn-Pb solder (melts ~183 °C – safer for old FR-4).
- Radial 105 °C capacitors from Nichicon, Panasonic FR/FC, Rubycon ZLJ or equivalent.
- Small flush-cutters, IPA, ESD wrist-strap.
💡 Extra Tips
[edit | edit source]- Socket clean-up: while the board is open, reseat the VIC, CPU & VIA ICs – oxidation here causes more faults than bad caps.
- Regulator upgrade (early board): consider replacing the TO-220 7805 with a modern drop-in switching regulator to cut internal heat by ~8 °C.
- Composite-mod recap: if you’ve removed the RF modulator in favour of direct composite, you can omit its two 100 µF caps – they only filter the RF can’s internal 5 V line.
- Cap spacing: Commodore often bent electrolytic leads outward – clip the old leads flush and use the holes; don’t enlarge them with a drill, the inner-layer vias run very close.
- Stagger your install: replace and test in sections (power, then audio/video). If something suddenly fails you’ll know which group to re-check.