Editing Commodore 64 Capacitor Replacement Guide

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'''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 ==
* '''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 ==
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 ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Early C64 Electrolytic Capacitors'''
! 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 ===
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) ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''250466 Capacitors'''
! 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 ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Short-Board Capacitor Set'''
! 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 ==
# '''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 ==
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Expected Rails – BASIC READY prompt, no cartridge'''
! 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 ==
* 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).  
* IPA, nylon brush, Kapton tape to insulate cap cans that sit against the RF shield.

== 💡 Extra Tips ==
* '''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.

== 🔗 Related Pages ==
* [[Commodore 64 Troubleshooting Guide]]  
* [[Commodore 64C Troubleshooting Guide]]  
* [[Commodore 64 Power-Supply Protector (C64 Saver)]]  

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