Jump to content

Commodore 64 Capacitor Replacement Guide: Difference between revisions

From RetroTechCollection
← Older edit

Josh (talk | contribs)

8 user groups
17,684 edits
undo
VisualWikitext
Rebuild from Commodore parts lists with page cites: drop invented Function column, fix B-3 C20 (0.22 uF film, not electrolytic), add C88 rev B/04 difference, B-2 note, power-section description, procedure and rail checks; add photo
Add Commodore diagnostic manual regulator input voltages and tolerance
 
Line 155: Line 155:
|}
|}


The two regulator ranges are the 78xx datasheet limits, not Commodore figures; Commodore's manual gives no tolerance for either rail.<ref name="smps" />
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>


== Related pages ==
== Related pages ==

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

[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

[edit | edit source]
  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

[edit | edit source]
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]

[edit | edit source]

References

[edit | edit source]
  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).
Retrieved from "https://wiki.retrotechcollection.com/index.php?title=Commodore_64_Capacitor_Replacement_Guide&oldid=17413"