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Recapping a '''[[Commodore 64]]''' restores stable supply rails, reduces heat stress on the MOS custom chips and cures a specific family of warm-up faults that Commodore itself documented.
[[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]].


'''Every value on this page is taken from Commodore's own parts lists''' in the [[Commodore 64 / 64C Service Manual|C64 / C64C Service Manual]] (March 1992).<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref> Cross-check against your own board's silkscreen before ordering — Commodore changed values between revisions, and boards were built with substitutions.
The ceramic, mica and film capacitors on these boards are not included. Commodore's lists give their values if one is damaged.


== Which board do you have? ==
== Identify the board ==
 
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>
The assembly number is silkscreened on the board. Commodore's own cross-reference:<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>


{| class="wikitable styled-table" style="width:100%; text-align:left;"
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''C64 mainboard revisions'''
|+'''Commodore 64 board assemblies'''
! Revision !! Assembly !! Notes
! Version !! Assembly !! Schematic !! Identifying factor (Commodore)
|-
|-
| Original || '''326298-01''' || 5-pin video connector, "long board"
| Original || 326298-01 || 326106 || 5-pin video connector (CN5)
|-
|-
| A (CR) || '''250407-01 / -04''' || 8-pin video connector, long board
| A (CR) || 250407 || 251138 || 8-pin video connector
|-
|-
| B || '''250425-01''' || Long board, cost-reduced
| B || 250425 || 251469 || 8-pin; reduced oscillator circuit
|-
|-
| B3 || '''250466-01''' || C64-B3
| B-2 || 250441-01 || 251469 || As B, with component location changes
|-
|-
| E || '''250469-01''' || C64-E "short board" — also used in the [[Commodore 64C]]
| 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
|}
|}


== Electrolytic capacitors by board revision ==
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.


These are the electrolytics — the parts that age. Ceramic and mica capacitors on these boards do not normally need replacing and are not listed.
== 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" />


=== 326298-01 — original long board ===
== Electrolytic capacitors by board ==
All values and ratings below are as printed in Commodore's parts lists. Fit at least the voltage rating shown.


{| class="wikitable styled-table" style="width:100%; text-align:left;"
=== 326298-01 (original) ===
|+'''326298-01 electrolytics'''<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>
{| class="wikitable styled-table" style="width:100%; text-align:center;"
! Ref !! Value !! Rating !! Tolerance !! Function
|+'''326298-01 electrolytics'''<ref name="sm326">''Service Manual C64/C64C'' (1992), "Parts List - PCB Assembly #326298", pp. 19-20.</ref>
! Ref !! Capacitance !! Rating !! Tolerance
|-
|-
| '''C19''' || 2200 µF || 16 V || || Main supply reservoir
| C19 || 2200 µF || 16 V ||
|-
|-
| '''C88''' || 470 µF || 50 V || || Supply filtering
| C88 || 470 µF || 50 V ||
|-
|-
| '''C90''' || 470 µF || 50 V || || Supply filtering
| C90 || 470 µF || 50 V ||
|-
|-
| '''C91''' || 100 µF || 16 V || || Regulator decoupling
| C91 || 100 µF || 16 V ||
|-
|-
| C8, C12–C15, C17, C24, C34, C57, C62, C64, C65, C94, C102 || 10 µF || 25 V || +50 % / −10 % || General decoupling
| C8, C12, C13, C14, C15, C17, C24, C34, C57, C62, C64, C65, C94, C102 || 10 µF || 25 V || +50 % / −10 %
|}
|}


=== 250407-04 — 8-pin long board ===
=== 250407 (A) ===
 
{| class="wikitable styled-table" style="width:100%; text-align:center;"
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''250407-04 electrolytics'''<ref name="sm407">''Service Manual C64/C64C'' (1992), "Parts List - PCB Assembly #250407-04", pp. 24-25.</ref>
|+'''250407-04 electrolytics'''<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>
! Ref !! Capacitance !! Rating !! Tolerance
! Ref !! Value !! Rating !! Tolerance !! Function
|-
|-
| '''C19''' || 2200 µF || 16 V || || Main supply reservoir
| C19 || 2200 µF || 16 V ||
|-
|-
| '''C88''' || '''1000 µF''' || '''25 V''' || || Supply filtering
| C88 || 1000 µF || 25 V ||
|-
|-
| '''C90''' || '''470 µF''' || '''50 V''' || || Supply filtering
| C90 || 470 µF || 50 V ||
|-
|-
| '''C91''' || '''100 µF''' || '''16 V''' || +50 % / −10 % || Regulator decoupling
| C91 || 100 µF || 16 V || +50 % / −10 %
|-
|-
| C8, C13–C15, C17, C24, C34, C57, C62, C65, C94, C102 || 10 µF || 25 V || +50 % / −10 % || General decoupling
| C8, C13, C14, C15, C17, C24, C34, C57, C62, C65, C94, C102 || 10 µF || 25 V || +50 % / −10 %
|-
|-
| C108 || 10 µF || 25 V || 20 % ||
| C108 || 10 µF || 25 V || 20 %
|}
|}


=== 250425-01 ===
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.


{| class="wikitable styled-table" style="width:100%; text-align:left;"
=== 250425 (B) and 250441 (B-2) ===
|+'''250425-01 electrolytics'''<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>
{| class="wikitable styled-table" style="width:100%; text-align:center;"
! Ref !! Value !! Rating !! Tolerance !! Function
|+'''250425-01 electrolytics'''<ref name="sm425">''Service Manual C64/C64C'' (1992), "Parts List - PCB Assembly #250425-01", pp. 29-30.</ref>
! Ref !! Capacitance !! Rating !! Tolerance !! Type
|-
|-
| '''C19''' || 2200 µF || 16 V || || Main supply reservoir
| C19 || 2200 µF || 16 V || || Electrolytic
|-
|-
| '''C88''' || 1000 µF || 25 V || || Supply filtering
| C88 || 1000 µF || 25 V || || Electrolytic
|-
|-
| '''C90''' || 470 µF || 50 V || || Supply filtering
| C90 || 470 µF || 50 V || || Electrolytic
|-
|-
| '''C91''' || 100 µF || 16 V || +50 % / −10 % || Regulator decoupling
| C91 || 100 µF || 16 V || +50 % / −10 % || Electrolytic
|-
|-
| C13 || 10 µF || 25 V || +50 % / −10 % || Decoupling
| C24 || 22 µF || 25 V || +50 % / −10 % || Electrolytic
|-
|-
| C24 || 22 µF || 25 V || +50 % / −10 % || Decoupling
| C13 || 10 µF || 25 V || +50 % / −10 % || Electrolytic
|-
|-
| '''C15''' || 4.7 µF || 16 V || 20 % || '''Tantalum''' — replace with tantalum
| C15 || 4.7 µF || 16 V || 20 % || Tantalum
|}
|}


=== 250466-01 — C64-B3 ===
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" />
 
Commodore part numbers are given here because this list prints them.<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>


{| class="wikitable styled-table" style="width:100%; text-align:left;"
=== 250466-01 (B-3) ===
|+'''250466-01 electrolytics'''<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>
{| class="wikitable styled-table" style="width:100%; text-align:center;"
! Ref !! Value !! Rating !! Package !! Commodore part no.
|+'''250466-01 electrolytics'''<ref name="smb3" />
! Ref !! Capacitance !! Rating !! Package !! Commodore part no.
|-
|-
| '''C19''' || 2200 µF || 16 V || Axial || 900101-33
| C19 || 2200 µF || 16 V || Axial || 900101-33
|-
|-
| '''C88''' || 1000 µF || 25 V || Axial || 900101-50
| C88 || 1000 µF || 25 V || Axial || 900101-50
|-
|-
| '''C90''' || '''470 µF''' || '''25 V''' || Axial || 900101-49
| C90 || 470 µF || 25 V || Axial || 900101-49
|-
|-
| '''C91''' || 100 µF || 16 V || Radial || 900100-40
| C91 || 100 µF || 16 V || Radial || 900100-40
|-
| C13 (C210) || 10 µF || 25 V || Radial || 900100-01 (sub 251079-16, 20 %)
|-
|-
| C24 || 22 µF || 25 V || Radial || 900100-24
| C24 || 22 µF || 25 V || Radial || 900100-24
|-
|-
| C200 || 2.2 µF || || Radial || 251079-06
| C13 (C210) || 10 µF || 25 V || Radial || 900100-01
|-
|-
| '''C15''' || 4.7 µF || 16 V || Radial || 900410-13 — '''tantalum''', 20 %
| C200 || 2.2 µF || not stated || Radial || 251079-06
|-
|-
| C20 || 0.2 µF || 100 V || Radial || 251875-01 — film, 20 %
| C15 || 4.7 µF tantalum || 16 V || Radial || 900410-13
|}
|}


'''Note the C90 rating change.''' It is 50 V on the 250407 and 250425 boards and '''25 V''' on the 250466. Either will work electrically; fit at least the rating printed for your board.
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" />


== Commodore's own capacitor-related faults ==
== 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>
The service manual's troubleshooting table names capacitors directly for two symptoms. Both are worth knowing before you assume a chip has failed:<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>


{| class="wikitable styled-table" style="width:100%; text-align:left;"
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Symptoms Commodore attributes to capacitors'''<ref name="sm">Commodore Business Machines, C64 / C64C Service Manual, March 1992, hosted at [[Commodore 64 / 64C Service Manual]]. Component-level parts lists give capacitance, voltage rating, tolerance and Commodore part number for every capacitor on each mainboard revision, and the manual carries Commodore's own symptom-to-component troubleshooting table.</ref>
|+'''Capacitor entries in Commodore's troubleshooting guide'''
! Symptom !! Commodore's check
! Symptom !! Commodore's check
|-
|-
| '''Intermittent display''' || '''C88''' — noted as a possible bad connection rather than a failed part, so reflow the joints before replacing it
| Intermittent display || C88 (possible bad connection)
|-
|-
| '''Black band scrolling through the screen once the system warms up''' || External power supply; '''C90, C88''', CR4; VR2 (5 V regulator)
| Black band scrolls through screen when system warms up || External power supply; C90, C88, CR4; VR2 (5 V regulator)
|-
|-
| White band scrolling down the screen (60 Hz hum) || External power supply; VR2 (5 V regulator)
| Wrong frequency || C70
|}
|}


That second row is the classic C64 recap symptom, and Commodore's own ordering is worth following: '''check the external supply first.''' The C64's 5 V rail comes in already regulated from the brick, and a failing brick produces the same scrolling band as tired board electrolytics.
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" />
 
== Procedure ==
# 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.
# Note the assembly number and use that board's list. Photograph the power section first.
# 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.
# 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.
# 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" />
# Power up and measure the regulator outputs.


== Before you start ==
== Checks after the recap ==
{| class="wikitable styled-table" style="width:80%; text-align:center;"
|+'''Supply measurements'''
! Point !! Nominal !! Acceptable
|-
| CN7 pin 5 (+5 V from the external supply) || 5.0 V || 4.95-5.10 V<ref name="c64wps" />
|-
| 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>
|-
| VR1 output (+12 V) || 12.0 V || 11.5-12.5 V<ref name="ti78" />
|}


* '''The power brick is the prime suspect in any C64 power fault.''' The original supplies are notorious for drifting high as they age and taking the MOS chips with them. Measure the 5 V output under load before blaming the board.
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>
* '''Work from your board's own silkscreen.''' Commodore substituted parts freely; the assembly number tells you which list applies, but the board is the final authority.
* Anti-static precautions throughout — the 6510, VIC-II, SID and PLA are irreplaceable in practical terms.
* See [[Capacitor Failure Symptoms]] for recognising a failed part, and [[Recommended Tools]] for the workshop kit.


== Related pages ==
== Related pages ==
 
* [[Commodore 64]] · [[Commodore 64C]] · [[Commodore 64C Capacitor Replacement Guide]]
* [[Commodore 64]] · [[Commodore 64C]] · [[Commodore 64 General Maintenance]] · [[Commodore 64 Troubleshooting Guide]]
* [[Commodore 64 General Maintenance]] · [[Commodore 64 Troubleshooting Guide]]
* '''[[Commodore C64 Service Manual]]''' — the source for every value on this page
* [[Commodore 64 / 64C Service Manual]] · [[Commodore 64 Technical Manual and Parts List]]
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]] · [[Battery Explosion, Capacitor or Corrosion Damage]]
* [[Commodore 64 Power-Supply Protector (C64 Saver)]]
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]]


== References ==
== References ==
<references />
<references />


[[Category:Commodore Systems]]
[[Category:Commodore Systems]]
[[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

[edit | edit source]

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

[edit | edit source]

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

[edit | edit source]

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

326298-01 (original)

[edit | edit source]
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)

[edit | edit source]
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

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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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