Commodore 64 Capacitor Replacement Guide
Recapping a Commodore 64 (all board revisions) restores stable power rails, lowers heat-stress on MOS chips and cures many “mystery” crashes, video glitches and SID noise. Because every C64 relies on an external +5 V DC / 9 VAC “brick” the on-board capacitors don’t fail quite as catastrophically as in computers with internal switch-modes, yet forty-year-old aluminium electrolytics are now well past their design life.
Visual Inspection & Failure Signs
[edit | edit source]- Bulging or leaning cans – especially the tall 4 700 µF reservoir (C88/C89).
- Leakage residue – brown/green crust at base of C90 (colour-RAM decoupler) is common.
- Ripple / hum on audio – audible buzz that follows screen brightness often tracks to dried-out C13 (SID analogue rail) or the RF-modulator’s 100 µF pair.
- Intermittent reset when warm – C15 (10 µF reset RC) high-ESR causes POR threshold to mis-trip.
If one capacitor shows trouble, replace all electrolytics on the board.
Commodore 64 Logic-Board Capacitor Lists
[edit | edit source]Unlike the VIC-20, the C64 underwent five major PCB generations. Commodore kept reference numbers fairly consistent, but always cross-check your silkscreen.
“Long boards” – Assy 326298 / 250407
[edit | edit source]| Board ref | Capacitance | Voltage | Purpose / rail |
|---|---|---|---|
| C88 | 4 700 µF | 16 V | Main +5 V bulk (from external PSU) |
| C90 | 1 000 µF | 16 V | Secondary 5 V at VIC/SID (reduces raster-noise) |
| C91 | 470 µF | 25 V | +12 V filter (SID 6581 & VIC 6567/9 analogue) |
| C13 | 220 µF | 25 V | 9 VAC ► +12 V doubler reservoir |
| C14 | 100 µF | 16 V | 9 VAC ► 5 V gate-array supply (PLA decouple) |
| C15 | 10 µF | 16 V | Power-on reset RC |
| C38 | 22 µF | 16 V | Audio path (SID DC-blocking) |
| C70 | 3.3 µF | 50 V | Chroma-coupling into RF modulator |
| C71,C72 | 100 µF | 16 V | RF modulator 5 V and audio buffer |
Very early NTSC boards mark C90 as 2 200 µF – Commodore standardised on 1 000 µF by Rev-B.
Assy 250425 – first “cost-reduced” long board
[edit | edit source]Same parts list as 250407 except C91 is omitted (12 V rail deleted when 8580 SID not yet adopted but cost saving began). Replace values exactly as found.
Assy 250466 – transitional board (8-chip DRAM → 2-chip DRAM)
[edit | edit source]| Ref | Capacitance | Voltage | Notes |
|---|---|---|---|
| C88 | 3 300 µF | 16 V | Commodore shaved value; 4 700 µF fits & improves ripple |
| C90 | 470 µF | 16 V | Lower current draw of HMOS chips allowed smaller part |
| C91 | 220 µF | 25 V | +12 V still present for 6581 SID (last board to use it) |
| Others | identical | – | Replace like-for-like |
“Short boards” – Assy 250469 (A/B/C) & 250469-Aldi
[edit | edit source]| Ref | Capacitance | Voltage | Rail / circuit |
|---|---|---|---|
| C88 | 2 200 µF | 10 V | Bulk +5 V (HMOS load ≈ 600 mA) |
| C89 | 1 000 µF | 10 V | Local decouple for VIC-II (8562/8565) |
| C90 | 330 µF | 10 V | SID 8580 analogue +9 V |
| C91 | *n/a* | – | 12 V rail deleted; do not fit tall cans! |
| C15 | 10 µF | 16 V | Reset timer (value unchanged) |
| C38 | 47 µF | 16 V | Audio DC-block (lower because 8580 output bias differs) |
| C70 | 2.2 µF | 50 V | Chroma-coupling (smaller foil can type) |
| C71,C72 | 47 µF | 16 V | RF modulator local filters |
The 250469-Aldi variant adds a linear 7812 + 470 µF 16 V can (C92) to power a 6581 SID on an otherwise 5 V-only board. If present, replace that extra capacitor as well.
Recapping Procedure
[edit | edit source]- Disassemble : remove three rear screws, two under the keyboard, pop keyboard hinges.
- Remove RF shield : desolder the six folded-tabs or snip and replace with screws on re-assembly.
- Label keyboard & LED leads.
- Desolder each capacitor with braid + flux. Commodore used thick, high-temperature solder; 375 °C is usually required.
- Fit new capacitors, matching polarity and lead-spacing (5 mm on small cans, 7.5 mm on main filters). Keep height ≤ 17 mm so the metal shield clears.
- Clean flux, inspect for bridges.
- First power-up through a current-limited bench supply or a C64 Saver inline protector in case the original brick is bad.
Post-Recap Voltage / Ripple Checks
[edit | edit source]| Test point (scope @20 MHz) | Long board | Short board | Max ripple (p-p) |
|---|---|---|---|
| +5 V (U6 PLA pin 24) | 4.95 – 5.10 V | same | < 50 mV |
| +12 V (SID pin 28) | 11.5 – 12.6 V | – | < 120 mV |
| +9 V (SID pin 28, 8580) | – | 8.7 – 9.3 V | < 100 mV |
| 9 VAC (user-port pins 10/11) | 8.5 – 10 V rms | same | sine-like |
A VIC-II picture that jitters or vertical “rainbow lines” usually means > 150 mV of 5 V ripple.
Recommended Tools & Parts
[edit | edit source]- 70 W temperature-controlled iron (2 mm chisel tip).
- Solder-wick and spring pump – double-layer ground pads are stubborn.
- Leaded 63/37 or SAC-lead-free solder (avoid cheap flux-core that leaves residue).
- 105 °C, low-ESR radial capacitors (Nichicon PW/PS, Panasonic FR/FC, Rubycon ZLH).
- ask an expert or the AI about specialty caps like polyester and hybrid types. These have many advantages like longer/unlimited life and less noise, especially with regard to the SID and VIC filters.
- IPA, nylon brush, Kapton tape to insulate cap cans that sit against the RF shield.
Extra Tips
[edit | edit source]- Check the brick first ! An over-voltage PSU kills fresh caps (and PLA / RAM) instantly.
- SID heat-pad : early boards rely on C90 as a “heat-sink standoff” – keep replacement can the same diameter so the RF-shield pad still contacts the SID.
- Retain RF modulator? If you have done an S-video or composite-bypass mod, you may delete C70/71/72 and the entire modulator 5 V line.
- Socket inspection : reseat VIC-II, SID, PLA after the recap – temperature swings often unseat them.
- Re-cap the 1541-II brick if bundled; its 4 700 µF can is the same age.
- Ask an expert or the AI about specialty caps like polyester and hybrid types. These have many advantages like longer/unlimited life and less noise, especially with regard to the SID and VIC filters.