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Created page with "<templatestyles src="Template:StyledTable/styles.css" /> '''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 w..."
 
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[[File:C64 Logic Board.jpg|thumb|360px|A 250407 "long board" (artwork 251137 rev. C). The large axial electrolytics in the power section at the right are C19, C88 and C90.]]
The tables below give the electrolytic capacitors on the '''[[Commodore 64]]''' long boards (assemblies 326298, 250407, 250425 and 250441) and on the 250466 (B-3) board. Every value comes from Commodore's own parts lists in the ''Service Manual C64/C64C'' (March 1992, PN-314001-03).<ref name="sm">Commodore Business Machines, ''Service Manual C64/C64C'', March 1992, PN-314001-03, hosted at [[Commodore 64 / 64C Service Manual]]. Board identification p. 17; parts lists for 326298 pp. 19-20, 250407-04 pp. 24-25, 250425-01 pp. 29-30, 250466-01 (B-3) pp. 34-35.</ref> The 250469 (E) board used in most [[Commodore 64C]] machines has a different power circuit and its own list in the [[Commodore 64C 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.''' 
The ceramic, mica and film capacitors on these boards are not included. Commodore's lists give their values if one is damaged.
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 ==
== Identify the board ==
* '''Bulging or leaning cans''' – especially the tall 4 700 µF reservoir (C88/C89).
The assembly number is printed on the board, usually near the cartridge port edge. Commodore's identification table:<ref name="smid">''Service Manual C64/C64C'' (1992), "C64 Board Identification" and "C64C Board Identification", p. 17.</ref>
* '''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.
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Commodore 64 board assemblies'''
! Version !! Assembly !! Schematic !! Identifying factor (Commodore)
|-
| Original || 326298-01 || 326106 || 5-pin video connector (CN5)
|-
| A (CR) || 250407 || 251138 || 8-pin video connector
|-
| B || 250425 || 251469 || 8-pin; reduced oscillator circuit
|-
| B-2 || 250441-01 || 251469 || As B, with component location changes
|-
| B-3 || 250466-01 || 252278 || Only two RAM chips, U9 and U10
|-
| E || 250469 || 252312 || BASIC and KERNAL combined in U4; memory controller at U8
|}
 
Commodore's table prints the B-3 assembly as "250446"; its parts list and board layout for the same board say 250466.<ref name="smb3">''Service Manual C64/C64C'' (1992), "Parts List, PCB Assembly #250466-01 C64-B3", pp. 34-35, and "B-3 Board Layout", p. 36.</ref> The manual has no separate parts list for the B-2 (250441): Commodore says all its circuits are those of the B (schematic 251469), with resistors R28, R29, R30, R36 and R48 replaced by resistor pack RP5 and diodes CR100-CR105 moved to CR9 and CR12-CR16.<ref name="smid" /> Use the 250425 list and check positions against the board.
 
== The power section ==
The external supply delivers regulated +5 V DC on CN7 pin 5 and 9 V AC on pins 6 and 7; pins 1, 2 and 3 are ground. The +5 V from the brick passes the power switch and powers the logic directly. On the board, the 9 V AC is used three ways:<ref name="smps">''Service Manual C64/C64C'' (1992), Circuit Theory, "The Power Supply", p. 4 (text and power-input diagram).</ref>
* Bridge rectifier CR4 and reservoir C19 feed VR2 (MC7805CT), whose output, "+5 V CAN", is filtered into Vvid for the video circuits and Vc for the clock circuits.
* The 9 V AC is "added to 9VDC through CR6, and rectified by CR5"; on Commodore's diagram C90 couples the AC into this circuit. The result is filtered by C88 and C89 and regulated to +12 V by VR1 (MC7812CT) for the VIC-II, the SID and the audio stages.
* CR4's output, unregulated, is the +9 V supply for the cassette motor circuit and, on the B board, the RF modulator.
C91 (100 µF) sits on the +5 V input after the power switch.<ref name="smps" />


== 📋 Commodore 64 Logic-Board Capacitor Lists ==
== Electrolytic capacitors by board ==
Unlike the VIC-20, the C64 underwent five major PCB generations.  Commodore kept reference numbers fairly consistent, but always cross-check your silkscreen.
All values and ratings below are as printed in Commodore's parts lists. Fit at least the voltage rating shown.


=== 🖥️ “Long boards” – Assy 326298 / 250407 ===
=== 326298-01 (original) ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Early C64 Electrolytic Capacitors'''
|+'''326298-01 electrolytics'''<ref name="sm326">''Service Manual C64/C64C'' (1992), "Parts List - PCB Assembly #326298", pp. 19-20.</ref>
! Board ref !! Capacitance !! Voltage !! Purpose / rail
! Ref !! Capacitance !! Rating !! Tolerance
|-
| C19 || 2200 µF || 16 V ||
|-
|-
| C88 || 4 700 µF || 16 V || Main +5 V bulk (from external PSU)
| C88 || 470 µF || 50 V ||
|-
|-
| C90 || 1 000 µF || 16 V || Secondary 5 V at VIC/SID (reduces raster-noise)
| C90 || 470 µF || 50 V ||
|-
|-
| C91 || 470 µF || 25 V || +12 V filter (SID 6581 & VIC 6567/9 analogue)
| C91 || 100 µF || 16 V ||
|-
| C8, C12, C13, C14, C15, C17, C24, C34, C57, C62, C64, C65, C94, C102 || 10 µF || 25 V || +50 % / −10 %
|}
 
=== 250407 (A) ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''250407-04 electrolytics'''<ref name="sm407">''Service Manual C64/C64C'' (1992), "Parts List - PCB Assembly #250407-04", pp. 24-25.</ref>
! Ref !! Capacitance !! Rating !! Tolerance
|-
|-
| C13 || 220 µF || 25 V || 9 VAC ► +12 V doubler reservoir
| C19 || 2200 µF || 16 V ||
|-
|-
| C14 || 100 µF || 16 V || 9 VAC ► 5 V gate-array supply (PLA decouple)
| C88 || 1000 µF || 25 V ||
|-
|-
| C15 || 10 µF || 16 V || Power-on reset RC
| C90 || 470 µF || 50 V ||
|-
|-
| C38 || 22 µF || 16 V || Audio path (SID DC-blocking)
| C91 || 100 µF || 16 V || +50 % / −10 %
|-
|-
| C70 || 3.3 µF || 50 V || Chroma-coupling into RF modulator
| C8, C13, C14, C15, C17, C24, C34, C57, C62, C65, C94, C102 || 10 µF || 25 V || +50 % / −10 %
|-
|-
| C71,C72 || 100 µF || 16 V || RF modulator 5 V and audio buffer
| C108 || 10 µF || 25 V || 20 %
|}
|}


''Very early NTSC boards mark C90 as 2 200 µF – Commodore standardised on 1 000 µF by Rev-B.''
C88 differs between documents. Commodore's 1983 drawing for assembly 250407 revision B lists C88 and C90 as 470 µF 50 V (part 900101-34), and C12 as a 10 µF electrolytic; the service manual's 250407-04 list gives C88 as 1000 µF 25 V and C12 as a 0.1 µF ceramic.<ref name="tm407">Commodore, ''Commodore 64 Computer Technical Manual'', P/N 990439, drawing 250407 rev. B, sheet 3 of 7 (PDF p. 6), items 47-50, hosted at [[Commodore 64 Technical Manual and Parts List]].</ref><ref name="sm407" /> Console5's kit list gives 470 µF at C88 for revision B and earlier boards and 1000 µF from revision C.<ref name="c5">Console5 TechWiki, [https://wiki.console5.com/wiki/Commodore_64 "Commodore 64"], capacitor lists for assemblies 326298, 250407, 250425, 250466 and 250469 (secondary source). Retrieved 2026-10-01.</ref> Read the part fitted to your board; a 1000 µF 25 V part covers either.
 
=== 🖥️ 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) ===
=== 250425 (B) and 250441 (B-2) ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''250466 Capacitors'''
|+'''250425-01 electrolytics'''<ref name="sm425">''Service Manual C64/C64C'' (1992), "Parts List - PCB Assembly #250425-01", pp. 29-30.</ref>
! Ref !! Capacitance !! Voltage !! Notes
! Ref !! Capacitance !! Rating !! Tolerance !! Type
|-
| C19 || 2200 µF || 16 V || || Electrolytic
|-
| C88 || 1000 µF || 25 V || || Electrolytic
|-
|-
| C88 || 3 300 µF || 16 V || Commodore shaved value; 4 700 µF fits & improves ripple
| C90 || 470 µF || 50 V || || Electrolytic
|-
|-
| C90 || 470 µF || 16 V || Lower current draw of HMOS chips allowed smaller part
| C91 || 100 µF || 16 V || +50 % / −10 % || Electrolytic
|-
|-
| C91 || 220 µF || 25 V || +12 V still present for 6581 SID (last board to use it)
| C24 || 22 µF || 25 V || +50 % / −10 % || Electrolytic
|-
|-
| Others || identical || – || Replace like-for-like
| C13 || 10 µF || 25 V || +50 % / −10 % || Electrolytic
|-
| C15 || 4.7 µF || 16 V || 20 % || Tantalum
|}
|}


=== 💾 “Short boards” – Assy 250469 (A/B/C) & 250469-Aldi ===
The 250425 has far fewer electrolytics than the earlier boards: positions such as C8, C14, C17, C34 and C57 are 0.1 µF ceramics or are not fitted.<ref name="sm425" />
 
=== 250466-01 (B-3) ===
{| class="wikitable styled-table" style="width:100%; text-align:center;"
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Short-Board Capacitor Set'''
|+'''250466-01 electrolytics'''<ref name="smb3" />
! Ref !! Capacitance !! Voltage !! Rail / circuit
! Ref !! Capacitance !! Rating !! Package !! Commodore part no.
|-
| C19 || 2200 µF || 16 V || Axial || 900101-33
|-
| C88 || 1000 µF || 25 V || Axial || 900101-50
|-
|-
| C88 || 2 200 µF || 10 V || Bulk +5 V (HMOS load ≈ 600 mA)
| C90 || 470 µF || 25 V || Axial || 900101-49
|-
|-
| C89 || 1 000 µF || 10 V || Local decouple for VIC-II (8562/8565)
| C91 || 100 µF || 16 V || Radial || 900100-40
|-
|-
| C90 || 330 µF || 10 V || SID 8580 analogue +9 V
| C24 || 22 µF || 25 V || Radial || 900100-24
|-
|-
| C91 || *n/a* || – || 12 V rail deleted; do '''not''' fit tall cans!
| C13 (C210) || 10 µF || 25 V || Radial || 900100-01
|-
|-
| C15 || 10 µF || 16 V || Reset timer (value unchanged)
| C200 || 2.2 µF || not stated || Radial || 251079-06
|-
|-
| C38 || 47 µF || 16 V || Audio DC-block (lower because 8580 output bias differs)
| C15 || 4.7 µF tantalum || 16 V || Radial || 900410-13
|}
 
C90 is rated 25 V on the B-3 and 50 V on the earlier boards. C20 on the B-3 is a 0.22 µF 100 V film capacitor, not an electrolytic.<ref name="smb3" />
 
== Faults Commodore traces to these parts ==
Commodore's troubleshooting table names capacitors in three symptoms.<ref name="smts">''Service Manual C64/C64C'' (1992), "64 Troubleshooting Guide", pp. 14-16.</ref>
 
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Capacitor entries in Commodore's troubleshooting guide'''
! Symptom !! Commodore's check
|-
|-
| C70 || 2.2 µF || 50 V || Chroma-coupling (smaller foil can type)
| Intermittent display || C88 (possible bad connection)
|-
|-
| C71,C72 || 47 µF  || 16 V || RF modulator local filters
| Black band scrolls through screen when system warms up || External power supply; C90, C88, CR4; VR2 (5 V regulator)
|-
| Wrong frequency || C70
|}
|}


''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.''
C70 is a 10 pF mica capacitor in the clock oscillator on the 326298, not an electrolytic.<ref name="sm326" /> The guide lists the external power supply first for the black-band symptom, and the same check heads its "white band scrolls down the screen (60 Hz hum)" entry, which names VR2 but no capacitor.<ref name="smts" />


== 🛠️ Recapping Procedure ==
== Procedure ==
# '''Disassemble :''' remove three rear screws, two under the keyboard, pop keyboard hinges.
# Measure the power supply's +5 V output before opening the machine. The C64-Wiki treats 4.95-5.10 V as normal and above 5.2 V as a failing supply; most machines it records as killed by their supply had seen more than 6 V.<ref name="c64wps">C64-Wiki, [https://www.c64-wiki.com/wiki/Power_Supply "Power Supply"], section "Failure". Retrieved 2026-10-01.</ref> Replace a high supply before working on the board.
# '''Remove RF shield :''' desolder the six folded-tabs or snip and replace with screws on re-assembly.
# Note the assembly number and use that board's list. Photograph the power section first.
# '''Label keyboard & LED leads.''' 
# Record the polarity of each part. C19, C88 and C90 are axial on the B-3 list; check which end carries the negative stripe before removing them.
# Desolder each capacitor with braid + flux. Commodore used thick, high-temperature solder; '''375 °C''' is usually required.
# Replace each electrolytic with the same capacitance and a voltage rating at least that shown. C15 on the 250425 and the B-3 is a tantalum part.
# 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 from the power section and inspect the joints on VR1, VR2 and CR4, which Commodore names in its "blank screen on power up" entry.<ref name="smts" />
# Clean flux, inspect for bridges.
# Power up and measure the regulator outputs.
# 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 ==
== Checks after the recap ==
{| class="wikitable styled-table" style="width:80%; text-align:center;"
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Expected Rails – BASIC READY prompt, no cartridge'''
|+'''Supply measurements'''
! Test point (scope @20 MHz) !! Long board !! Short board !! Max ripple (p-p)
! Point !! Nominal !! Acceptable
|-
|-
| +5 V (U6 PLA pin 24) || 4.95 – 5.10 V || same || < 50 mV
| CN7 pin 5 (+5 V from the external supply) || 5.0 V || 4.95-5.10 V<ref name="c64wps" />
|-
|-
| +12 V (SID pin 28) || 11.5 – 12.6 V || – || < 120 mV
| VR2 output (+5 V CAN) || 5.0 V || 4.8-5.2 V<ref name="ti78">Texas Instruments, ''LM340, LM340A and LM7805 Family Wide VIN 1.5-A Fixed Voltage Regulators'', SNOSBT0L (revised September 2016), tables 6.6 and 6.7, output voltage at TJ = 25 °C. Commodore fitted Motorola MC7805CT and MC7812CT parts of the same 78xx type.</ref>
|-
|-
| +9 V (SID pin 28, 8580) || – || 8.7 – 9.3 V || < 100 mV
| VR1 output (+12 V) || 12.0 V || 11.5-12.5 V<ref name="ti78" />
|-
| 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.''
The two regulator ranges are the 78xx datasheet limits. Commodore's diagnostic manual takes all its readings "within a +/-10% tolerance" and expects +9 to +12 V DC at VR2's input and +15 to +18 V DC at VR1's input.<ref name="dm">Commodore Business Machines, ''C64 Diagnostic Instruction and Troubleshooting Manual, Assembly #326070-01'', 1992, Section 2, pp. 2-1 and 2-3, hosted at [[Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01)]].</ref>
 
== 🧰 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 ==
== Related pages ==
* '''Check the brick first !''' An over-voltage PSU kills fresh caps (and PLA / RAM) instantly. 
* [[Commodore 64]] · [[Commodore 64C]] · [[Commodore 64C Capacitor Replacement Guide]]
* '''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. 
* [[Commodore 64 General Maintenance]] · [[Commodore 64 Troubleshooting Guide]]
* '''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. 
* [[Commodore 64 / 64C Service Manual]] · [[Commodore 64 Technical Manual and Parts List]]
* '''Socket inspection :''' reseat VIC-II, SID, PLA after the recap – temperature swings often unseat them. 
* [[Commodore 64 Power-Supply Protector (C64 Saver)]]
* '''Re-cap the 1541-II brick''' if bundled; its 4 700 µF can is the same age.
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]]


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


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

Latest revision as of 09:52, 1 October 2026

A 250407 "long board" (artwork 251137 rev. C). The large axial electrolytics in the power section at the right are C19, C88 and C90.

The tables below give the electrolytic capacitors on the Commodore 64 long boards (assemblies 326298, 250407, 250425 and 250441) and on the 250466 (B-3) board. Every value comes from Commodore's own parts lists in the Service Manual C64/C64C (March 1992, PN-314001-03).[1] The 250469 (E) board used in most Commodore 64C machines has a different power circuit and its own list in the Commodore 64C Capacitor Replacement Guide.

The ceramic, mica and film capacitors on these boards are not included. Commodore's lists give their values if one is damaged.

Identify the board

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The assembly number is printed on the board, usually near the cartridge port edge. Commodore's identification table:[2]

Commodore 64 board assemblies
Version Assembly Schematic Identifying factor (Commodore)
Original 326298-01 326106 5-pin video connector (CN5)
A (CR) 250407 251138 8-pin video connector
B 250425 251469 8-pin; reduced oscillator circuit
B-2 250441-01 251469 As B, with component location changes
B-3 250466-01 252278 Only two RAM chips, U9 and U10
E 250469 252312 BASIC and KERNAL combined in U4; memory controller at U8

Commodore's table prints the B-3 assembly as "250446"; its parts list and board layout for the same board say 250466.[3] The manual has no separate parts list for the B-2 (250441): Commodore says all its circuits are those of the B (schematic 251469), with resistors R28, R29, R30, R36 and R48 replaced by resistor pack RP5 and diodes CR100-CR105 moved to CR9 and CR12-CR16.[2] Use the 250425 list and check positions against the board.

The power section

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The external supply delivers regulated +5 V DC on CN7 pin 5 and 9 V AC on pins 6 and 7; pins 1, 2 and 3 are ground. The +5 V from the brick passes the power switch and powers the logic directly. On the board, the 9 V AC is used three ways:[4]

  • Bridge rectifier CR4 and reservoir C19 feed VR2 (MC7805CT), whose output, "+5 V CAN", is filtered into Vvid for the video circuits and Vc for the clock circuits.
  • The 9 V AC is "added to 9VDC through CR6, and rectified by CR5"; on Commodore's diagram C90 couples the AC into this circuit. The result is filtered by C88 and C89 and regulated to +12 V by VR1 (MC7812CT) for the VIC-II, the SID and the audio stages.
  • CR4's output, unregulated, is the +9 V supply for the cassette motor circuit and, on the B board, the RF modulator.

C91 (100 µF) sits on the +5 V input after the power switch.[4]

Electrolytic capacitors by board

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All values and ratings below are as printed in Commodore's parts lists. Fit at least the voltage rating shown.

326298-01 (original)

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326298-01 electrolytics[5]
Ref Capacitance Rating Tolerance
C19 2200 µF 16 V
C88 470 µF 50 V
C90 470 µF 50 V
C91 100 µF 16 V
C8, C12, C13, C14, C15, C17, C24, C34, C57, C62, C64, C65, C94, C102 10 µF 25 V +50 % / −10 %

250407 (A)

[edit | edit source]
250407-04 electrolytics[6]
Ref Capacitance Rating Tolerance
C19 2200 µF 16 V
C88 1000 µF 25 V
C90 470 µF 50 V
C91 100 µF 16 V +50 % / −10 %
C8, C13, C14, C15, C17, C24, C34, C57, C62, C65, C94, C102 10 µF 25 V +50 % / −10 %
C108 10 µF 25 V 20 %

C88 differs between documents. Commodore's 1983 drawing for assembly 250407 revision B lists C88 and C90 as 470 µF 50 V (part 900101-34), and C12 as a 10 µF electrolytic; the service manual's 250407-04 list gives C88 as 1000 µF 25 V and C12 as a 0.1 µF ceramic.[7][6] Console5's kit list gives 470 µF at C88 for revision B and earlier boards and 1000 µF from revision C.[8] Read the part fitted to your board; a 1000 µF 25 V part covers either.

250425 (B) and 250441 (B-2)

[edit | edit source]
250425-01 electrolytics[9]
Ref Capacitance Rating Tolerance Type
C19 2200 µF 16 V Electrolytic
C88 1000 µF 25 V Electrolytic
C90 470 µF 50 V Electrolytic
C91 100 µF 16 V +50 % / −10 % Electrolytic
C24 22 µF 25 V +50 % / −10 % Electrolytic
C13 10 µF 25 V +50 % / −10 % Electrolytic
C15 4.7 µF 16 V 20 % Tantalum

The 250425 has far fewer electrolytics than the earlier boards: positions such as C8, C14, C17, C34 and C57 are 0.1 µF ceramics or are not fitted.[9]

250466-01 (B-3)

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250466-01 electrolytics[3]
Ref Capacitance Rating Package Commodore part no.
C19 2200 µF 16 V Axial 900101-33
C88 1000 µF 25 V Axial 900101-50
C90 470 µF 25 V Axial 900101-49
C91 100 µF 16 V Radial 900100-40
C24 22 µF 25 V Radial 900100-24
C13 (C210) 10 µF 25 V Radial 900100-01
C200 2.2 µF not stated Radial 251079-06
C15 4.7 µF tantalum 16 V Radial 900410-13

C90 is rated 25 V on the B-3 and 50 V on the earlier boards. C20 on the B-3 is a 0.22 µF 100 V film capacitor, not an electrolytic.[3]

Faults Commodore traces to these parts

[edit | edit source]

Commodore's troubleshooting table names capacitors in three symptoms.[10]

Capacitor entries in Commodore's troubleshooting guide
Symptom Commodore's check
Intermittent display C88 (possible bad connection)
Black band scrolls through screen when system warms up External power supply; C90, C88, CR4; VR2 (5 V regulator)
Wrong frequency C70

C70 is a 10 pF mica capacitor in the clock oscillator on the 326298, not an electrolytic.[5] The guide lists the external power supply first for the black-band symptom, and the same check heads its "white band scrolls down the screen (60 Hz hum)" entry, which names VR2 but no capacitor.[10]

Procedure

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  1. Measure the power supply's +5 V output before opening the machine. The C64-Wiki treats 4.95-5.10 V as normal and above 5.2 V as a failing supply; most machines it records as killed by their supply had seen more than 6 V.[11] Replace a high supply before working on the board.
  2. Note the assembly number and use that board's list. Photograph the power section first.
  3. Record the polarity of each part. C19, C88 and C90 are axial on the B-3 list; check which end carries the negative stripe before removing them.
  4. Replace each electrolytic with the same capacitance and a voltage rating at least that shown. C15 on the 250425 and the B-3 is a tantalum part.
  5. Clean flux from the power section and inspect the joints on VR1, VR2 and CR4, which Commodore names in its "blank screen on power up" entry.[10]
  6. Power up and measure the regulator outputs.

Checks after the recap

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Supply measurements
Point Nominal Acceptable
CN7 pin 5 (+5 V from the external supply) 5.0 V 4.95-5.10 V[11]
VR2 output (+5 V CAN) 5.0 V 4.8-5.2 V[12]
VR1 output (+12 V) 12.0 V 11.5-12.5 V[12]

The two regulator ranges are the 78xx datasheet limits. Commodore's diagnostic manual takes all its readings "within a +/-10% tolerance" and expects +9 to +12 V DC at VR2's input and +15 to +18 V DC at VR1's input.[13]

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References

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  1. ↑ Commodore Business Machines, Service Manual C64/C64C, March 1992, PN-314001-03, hosted at Commodore 64 / 64C Service Manual. Board identification p. 17; parts lists for 326298 pp. 19-20, 250407-04 pp. 24-25, 250425-01 pp. 29-30, 250466-01 (B-3) pp. 34-35.
  2. ↑ 2.0 2.1 Service Manual C64/C64C (1992), "C64 Board Identification" and "C64C Board Identification", p. 17.
  3. ↑ 3.0 3.1 3.2 Service Manual C64/C64C (1992), "Parts List, PCB Assembly #250466-01 C64-B3", pp. 34-35, and "B-3 Board Layout", p. 36.
  4. ↑ 4.0 4.1 Service Manual C64/C64C (1992), Circuit Theory, "The Power Supply", p. 4 (text and power-input diagram).
  5. ↑ 5.0 5.1 Service Manual C64/C64C (1992), "Parts List - PCB Assembly #326298", pp. 19-20.
  6. ↑ 6.0 6.1 Service Manual C64/C64C (1992), "Parts List - PCB Assembly #250407-04", pp. 24-25.
  7. ↑ Commodore, Commodore 64 Computer Technical Manual, P/N 990439, drawing 250407 rev. B, sheet 3 of 7 (PDF p. 6), items 47-50, hosted at Commodore 64 Technical Manual and Parts List.
  8. ↑ Console5 TechWiki, "Commodore 64", capacitor lists for assemblies 326298, 250407, 250425, 250466 and 250469 (secondary source). Retrieved 2026-10-01.
  9. ↑ 9.0 9.1 Service Manual C64/C64C (1992), "Parts List - PCB Assembly #250425-01", pp. 29-30.
  10. ↑ 10.0 10.1 10.2 Service Manual C64/C64C (1992), "64 Troubleshooting Guide", pp. 14-16.
  11. ↑ 11.0 11.1 C64-Wiki, "Power Supply", section "Failure". Retrieved 2026-10-01.
  12. ↑ 12.0 12.1 Texas Instruments, LM340, LM340A and LM7805 Family Wide VIN 1.5-A Fixed Voltage Regulators, SNOSBT0L (revised September 2016), tables 6.6 and 6.7, output voltage at TJ = 25 °C. Commodore fitted Motorola MC7805CT and MC7812CT parts of the same 78xx type.
  13. ↑ Commodore Business Machines, C64 Diagnostic Instruction and Troubleshooting Manual, Assembly #326070-01, 1992, Section 2, pp. 2-1 and 2-3, hosted at Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01).
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