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Rebuild from the 250469-01 parts list and schematic 252312: capacitor table was wrong in every row (C90 and C88 are ceramics on this board, the 1000uF is C63, the 220uF parts are C43/C65, the 22uF is C44 at 50V), no SMD tantalums exist on the short board, SuperPLA is 251715-01 and does not contain the colour RAM (2114 at U19 not U16), 8500 +5V is pin 6 not pin 40 and phi2 is pin 39 not pin 6, SID Vdd comes from zener CR7 (9.6V/12.6V by SID type) with the matching filter caps and R8, truncated...
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[[File:Commodore64C_Motherboard_250469.jpg|thumb|400px|Commodore 64C short board, assembly 250469.]]


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The '''[[Commodore 64C]]''' short board is the simplest C64 mainboard Commodore built: two DRAMs, one combined ROM, a memory controller in place of most of the glue logic, and no 12&nbsp;V regulator. It is also the revision most often described wrongly, because maintenance notes written for the long board get copied onto it. This page covers routine care specific to the '''250469 E board'''.
[[File:Commodore64C Motherboard 250469.jpg|thumb|Commodore 64C (250469) motherboard]]
ย 
Proper maintenance is essential to preserve the reliability and longevity of your '''Commodore 64C'''. As these machines approach four decades of service, routine care, cleaning, and preventive checks are vital to avoid common failures.
'''The electrical figures here are taken from Commodore's own [[Commodore 64 / 64C Service Manual|C64 / C64C Service Manual]]''' (March 1992, PN-314001-03) โ€” the parts list for PCB assembly 250469-01 and schematic 252312.<ref name="sm">Commodore Business Machines, ''C64 / C64C Service Manual'', March 1992, PN-314001-03, hosted at [[Commodore 64 / 64C Service Manual]]. Parts list for PCB assembly 250469-01 (C64-E) and schematic 252312, giving the IC positions, the power-input wiring, the SID supply arrangement and the build differences between 6581 and 8580 fits.</ref>


== Regular Cleaning ==
For fault-finding see [[Commodore 64C Troubleshooting Guide]]; for the machine itself see [[Commodore 64C]]; for the long boards see [[Commodore 64 General Maintenance]].


=== Case and Keyboard ===
== Confirm you have a short board ==
* Wipe the C64Cโ€™s ABS plastic case with a '''damp microfibre cloth''' and a drop of mild dish soap.
* Avoid abrasive cleaners or strong solvents that can scratch or discolour the lighter โ€œC64Cโ€ plastics.
* Keycaps can be removed vertically for deep cleaning. Clean key plungers and stems with 99% isopropyl alcohol.
* For yellowed keys or case, '''retro-brite''' is possible, but monitor temperature and exposure time closely to avoid warping.
* Lubricate the space-bar stabiliser wire with a plastic-safe grease if sticky.


=== Internal Cleaning ===
Commodore's identifying factor for the '''E''' board is that the '''KERNAL and BASIC ROMs are combined into U4''' and there is a '''new IC memory controller at U8'''. The layout page records PCB assy no.&nbsp;250469, PCB no.&nbsp;252311 Rev.&nbsp;3.<ref name="sm" />
* Disconnect the power supply and allow the system to sit for at least 5 minutes before opening.
* Use compressed air or a soft anti-static brush to remove dust from the motherboard, cartridge port, and expansion connectors.
* For stubborn grime, gently wipe the PCB with isopropyl alcohol and a lint-free cloth.
* Avoid excessive moisture and ensure the board is fully dry before reassembly.


=== Edge Connectors and Ports ===
If your board has eight RAM chips and separate BASIC and KERNAL ROMs, it is a long board and the wrong page is open.
* Clean cartridge, user port, and expansion edge connectors with isopropyl alcohol and a pink pencil eraser.
* Inspect for bent pins or corrosion, especially on the cartridge and cassette ports.


== Power Supply and Voltage Checks ==
== Power ==


The original Commodore 64C power supply (โ€œbrickโ€) is notorious for overvoltage failures that can destroy critical ICs.
The short board takes the same 7-pin DIN supply as the bread bin: '''regulated +5&nbsp;V DC and 9&nbsp;V AC'''.


=== Safe Power Supply Practices ===
{| class="wikitable styled-table" style="width:80%; text-align:left;"
* Always measure the power supply output '''before each session''' using a digital multimeter.
|+'''Power input CN7 on the E board'''<ref name="sm" />
* Acceptable ranges:
! Pin !! Function
{| class="wikitable styled-table" style="width:60%;"
! Pin !! Function !! Healthy Range
|-
|-
| 1 (red) || +5 V DC || 4.95 โ€“ 5.20 V
| 1, 2, 3 || Ground
|-
|-
| 2 (white) || GND || 0 V
| 4, 5 || +5 V DC, regulated, from the brick &mdash; switched by SW1, filtered by C58 (100 &micro;F 16 V)
|-
|-
| 6 (yellow) || 9 VAC || 9.0 โ€“ 11.0 V rms
| 6, 7 || 9 V AC &mdash; through fuse F1 (1.5 A) and line filter L1 to bridge CR2
|}
|}
* If the +5 V DC rail exceeds 5.3 V, '''stop using the supply immediately'''.
* Modern replacements (e.g. C64RMK2, Ray Carlsen adapters) or DIY bricks with overvoltage protection are strongly recommended.


=== Voltage Test Points ===
'''The E board generates no +12&nbsp;V rail.''' The 9&nbsp;V AC is rectified by CR2 into C63 to make the 9&nbsp;V unregulated rail, which feeds the SID supply, the cassette motor drive and the audio amplifier Q3.<ref name="sm" />
* Measure +5 V DC at the 8500 CPU pin 40 or at the power input pins on the motherboard.
* 9 VAC can be checked at the user port pins 10 (AC) and 12 (AC return).
* The shortboard C64C (250469) does not generate +12 V internally; only +5 V and 9 VAC are present.


== Connector & Socket Corrosion ==
=== The SID supply is a zener, not a regulator ===


Age and humidity can cause oxidation on sockets and connectors, leading to intermittent faults.
On the E board the SID's Vdd comes from the 9&nbsp;V unregulated rail through pass transistor '''Q5''' and zener '''CR7'''. Commodore's note on schematic 252312 gives the zener by SID type:<ref name="sm" />


=== Areas to Inspect ===
{| class="wikitable styled-table" style="width:80%; text-align:left;"
* '''IC sockets''': Especially PLA/SuperPLA, SID, VIC-II, and CIAs.
! SID fitted !! CR7 !! Filter capacitors C70, C71 !! Filter capacitors C80, C81 !! R8
* '''Cartridge and user port edge connectors'''
|-
* '''Keyboard matrix connector and joystick ports'''
| '''6581''' || 12.6 V || 470 pF || 1800 pF || Fitted
* '''Power input socket'''
|-
| '''8580''' || 9.6 V || 22000 pF || 2200 pF || '''Removed'''
|}


=== Cleaning Procedure ===
'''This is the thing to get right before swapping a SID.''' Fitting an 8580 to a board built for a 6581 puts 12.6&nbsp;V on a 9&nbsp;V part.
* Reseat all socketed chips annually to wipe contacts.
* Apply a small amount of DeoxIT or contact cleaner to IC pins and edge connectors.
* For stubborn oxidation, use a fibreglass pen or soft brush, taking care not to damage traces or pads.


== Capacitor Health & Replacement Guidance ==
=== Supply checks ===


While the C64C shortboard (ASSY 250469) is more reliable than earlier models, some electrolytic capacitors may still degrade with age.
'''Measure the brick's +5&nbsp;V output before plugging it into the machine.''' There is no regulator on the board between it and every chip. The original supplies are potted and fail without warning. See [[Commodore 64 Power-Supply Protector (C64 Saver)]].


=== Capacitors to Inspect ===
{| class="wikitable styled-table" style="width:100%; text-align:left;"
{| class="wikitable styled-table" style="width:70%;"
|+'''Go/no-go checks'''<ref name="sm" />
! Location !! Value & Type !! Function
! Signal !! Where !! Expected
|-
| '''+5 V''' || 8500 CPU (U6) '''pin 6''' (VCC). Pin 21 is GND || 4.9 &ndash; 5.1 V
|-
| '''RESET''' || 8500 '''pin 40''' || Low at power-up, then +5 V
|-
| '''&Phi;0 in''' || 8500 '''pin 1''' || 1.023 MHz NTSC / 0.985 MHz PAL
|-
| '''&Phi;2 out''' || 8500 '''pin 39''' || Same frequency
|-
| '''VIC-II supply''' || VIC-II (U7) '''pin 40''' (VCC) and '''pin 13''' (VDD) || +5 V; the HMOS VIC-II needs no 12 V
|-
|-
| C90 (near power input) || 1000 ยตF / 16 V electrolytic || +5 V rail smoothing
| '''SID supply''' || SID (U9) '''pin 28''' (VDD) || 9 V with an 8580, 12 V with a 6581
|-
|-
| C88 (modulator) || 22 ยตF / 16 V electrolytic || RF output filtering
| '''SID audio out''' || SID '''pin 27'''; audio in is pin 26 || Signal present when a voice is running
|-
|-
| C91, C92 (rectifier path) || 220 ยตF / 16 V electrolytic || 9 VAC rectification
| '''+5 V''' (user port) || CN2 '''pin 2'''; ground on pins 1 and 12 || 4.9 &ndash; 5.1 V
|-
|-
| SMD tantalum caps (main board) || Various || Decoupling (rarely fail)
| '''9 V AC''' || CN2 '''pins 10 to 11''' || 9 &ndash; 11 V rms
|}
|}
* Inspect for bulging, leakage, or corrosion.
* Replace suspect electrolytics with quality low-ESR types; observe polarity.
* The modulator contains small electrolytics that can cause video shimmer or loss of audio if failed.


''See [[Commodore 64C Capacitor Replacement Guide]] for detailed part numbers and procedures.''
'''Pin 40 of the 8500 is RESET and pin 6 is Vcc.''' Earlier versions of this page told readers to measure +5&nbsp;V at pin 40 and the clock at pin 6; both are wrong, and pin 3 is IRQ, not reset.


== Common Failure Points ==
== Chip positions ==


{| class="wikitable styled-table" style="width:100%; text-align:center;"
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''C64C Short Board (250469) โ€“ Typical Faults'''
|+'''250469-01 integrated circuits'''<ref name="sm" />
! Component !! Symptom !! Quick Check / Solution
! Position !! Part !! Commodore part no.
|-
| '''U6''' || 8500 CPU || 318012-01
|-
| '''U7''' || VIC-II, 8567 or 8562 || 318014-01 / 318027-01
|-
| '''U9''' || 8580 SID (or 6581 on some builds) || 318013-01 / 906112-01
|-
| '''U1, U2''' || 6526 CIA || 906108-01
|-
| '''U8''' || Memory controller, the "Super PLA" || 251715-01
|-
|-
| '''SuperPLA (252535-01)''' || Black screen, random crash, no boot || Swap with known good PLA or modern replacement (PLAnkton, Ultimate PLA)
| '''U4''' || Combined BASIC + KERNAL ROM (23128B) || 251913-01
|-
|-
| '''SID (8580R5)''' || No sound, stuck keys, audio distortion || Touch pin 27 for hum; swap with working SID if possible
| '''U5''' || Character ROM (2332C) || 901225-01
|-
|-
| '''VIC-II (8565R2)''' || No video, bad colour, vertical bars || Check for heat; ensure good contact and +5 V at pin 40
| '''U10, U11''' || DRAM, 64K &times; 4 (50464-150) || 390083-07
|-
|-
| '''CIA (6526A)''' || Dead keyboard, joystick, or IEC || Swap CIAs (U1/U2); fault follows chip if defective
| '''U19''' || Colour RAM, 2114 || 901453-07 / -09
|-
|-
| '''DRAM (41464 ร—2)''' || Random characters, memory errors, crash || Use Dead Test cartridge to identify faulty chip
| '''U20''' || 8701 clock generator || 251527-08 / -09
|-
|-
| '''Modulator Electrolytics''' || Shimmering video, weak audio || Replace C88 and C89 in modulator
| U3, U22, U23, U18, U21 || 74LS08, 7406/7416, 74LS14, 4066 ||
|}
|}


== Device-Specific Subsystems ==
Two corrections worth making explicitly, because both appeared on this page before:
ย 
* '''The colour RAM is a separate 2114 at U19.''' It is not inside the memory controller.<ref name="sm" />
* '''The character ROM is U5.''' U3 is a 74LS08.<ref name="sm" />
ย 
== Capacitors ==
ย 
'''There are no SMD tantalums on the 250469 board.''' Commodore's parts list is entirely through-hole: axial and radial aluminium electrolytics, ceramics and one trimmer.<ref name="sm" />
ย 
The reservoir is '''C63''' (1000&nbsp;&micro;F 16&nbsp;V, or 2200&nbsp;&micro;F on the France build), and the other electrolytics are C66, C43, C65, C58, C36, C44, C77 and C59. '''C88 and C90 on this board are ceramics''', not electrolytics โ€” 220&nbsp;pF and 470&nbsp;pF respectively โ€” so a note telling you to replace "C88 in the modulator" is describing a long board.<ref name="sm" />
ย 
'''See [[Commodore 64C Capacitor Replacement Guide]] for the full list with Commodore part numbers.''' It is not repeated here, so that there is only one place on this wiki to correct.
ย 
See [[Capacitor Failure Symptoms]] for recognising a failed part.
ย 
== Regular cleaning ==
ย 
=== Case and keyboard ===
ย 
* Wipe the lighter C64C plastics with a damp microfibre cloth and a drop of mild detergent. Avoid solvents; the C64C's finish marks more easily than the bread bin's.
* Key caps pull vertically. Clean the plungers and stems with isopropyl alcohol.
* For yellowing see [[Retrobrite]], and weigh the cosmetic gain against the embrittlement.
* Lubricate the space-bar stabiliser wire with a plastic-safe grease if it sticks.
ย 
=== Internal ===
ย 
* Disconnect the supply and let the board sit before opening it.
* Blow dust out with dry air; brush with a soft anti-static brush.
* Wipe stubborn grime with isopropyl alcohol on a lint-free cloth, without flooding, and let it dry fully before reassembly.
ย 
=== Edge connectors and sockets ===
ย 
* Clean the cartridge, user and expansion connectors with isopropyl alcohol. '''Do not use an abrasive eraser''' โ€” the gold plating is thin.
* Reseat the socketed ICs annually to wipe the contacts. On the E board the sockets Commodore fits are 16, 28 and 40 pin.<ref name="sm" />
* Inspect for bent contacts on the cartridge and cassette ports.
ย 
== Common faults on the short board ==
ย 
{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Component !! Symptom !! First check
|-
| '''Power supply''' || Anything from a dead machine to random crashes to dead chips || Measure the brick's +5 V output on its own, before connecting it
|-
| '''Memory controller (U8)''' || Black screen, no boot, random crashes || Feel for heat; substitute a known-good part
|-
| '''SID (U9)''' || No sound, distortion || Check Vdd at pin 28 against the CR7 table above, then the signal at pin 27
|-
| '''VIC-II (U7)''' || No video, wrong colours, vertical bars || Check +5 V at pins 40 and 13; feel for heat
|-
| '''CIA (U1, U2)''' || Dead keyboard, joystick or IEC || Swap U1 and U2; if the fault follows the chip you have found it
|-
| '''DRAM (U10, U11)''' || Random characters, memory errors || Dead-test cartridge; see [[Commodore Test Cartridge Index]]
|-
| '''Colour RAM (U19)''' || Correct characters, wrong colours ||
|-
| '''Character ROM (U5)''' || Correct layout, corrupted glyphs || Check the socket before the chip
|-
| '''8701 clock generator (U20)''' || No clock, no display || Check for activity at U20 and at 8500 pin 1
|}


=== Keyboard Matrix ===
== Cooling and ventilation ==
* The C64C keyboard uses a flexible membrane and ribbon cable; inspect for cracked traces or corrosion at the connector.
* Clean contacts with isopropyl alcohol; repair broken traces with conductive ink if necessary.


=== Cooling and Ventilation ===
The short board runs cooler than the long boards โ€” there is no 12&nbsp;V regulator dissipating on it โ€” but the VIC-II, the SID and the memory controller still get warm. Small self-adhesive heatsinks are cheap insurance. Keep the top vents clear.
* The C64C runs cooler than earlier models, but the VIC-II, SID, and PLA chips still benefit from small self-adhesive heatsinks.
* Ensure at least 2 cm clearance above the top vents; avoid stacking objects on the case.


=== RF Modulator ===
== Preventive checklist ==
* Video or audio issues may originate from failing electrolytics inside the metal modulator can.
* If composite video is used exclusively, consider bypassing or replacing the modulator for improved quality.


== Recommended Tools & Consumables ==
# '''Test the power supply output before every session''' with an original brick; replace or protect it if it is out of spec.
# Inspect and reflow the solder joints around the power input and the switch.
# Reseat the socketed chips annually.
# Clean the cartridge and user-port connectors.
# Check the keyboard ribbon and membrane for cracked traces or corrosion; conductive ink repairs broken traces.
# Replace the electrolytics if the machine shows video noise or instability once warm โ€” '''after''' clearing the supply.


* ESD wrist strap and anti-static mat
== Tools ==
* Digital multimeter (for voltage checks)
* Soldering iron with fine tip, flux, and desolder braid (for capacitor or socket replacement)
* Isopropyl alcohol (99%) and lint-free cloths
* Compressed air and soft anti-static brush
* DeoxIT or similar contact cleaner
* Diagnostic cartridges: '''C64 Dead Test 781220''' and '''Diagnostic Rev. 586220'''
* Small fibreglass pen or pink eraser (for edge connectors)
* Plastic-safe grease (for stabiliser wire)
* Conductive trace pen (for keyboard repairs)


== Preventive Maintenance Checklist ==
* Anti-static strap and mat; digital multimeter
* Fine-tipped soldering iron, flux, braid, desoldering pump
* Isopropyl alcohol (99&nbsp;%), lint-free cloths, compressed air, soft brush
* Contact cleaner suitable for edge connectors
* Conductive trace pen for keyboard repairs
* A diagnostic cartridge โ€” see [[Commodore Test Cartridge Index]]


# '''Test power supply''' output before every use; replace if out of spec.
See also [[Recommended Tools]].
# '''Inspect and reflow solder joints''' on the power input and voltage regulator area if dull or cracked.
# '''Reseat socketed chips''' annually; clean pins and sockets as needed.
# '''Clean cartridge and user port connectors''' with isopropyl alcohol.
# '''Replace electrolytic capacitors''' in the modulator and power input if showing signs of failure.
# '''Add heatsinks''' to VIC-II, SID, and PLA/SuperPLA for improved thermal longevity.
# '''Maintain ventilation''' by keeping vents clear and avoiding heat build-up.
# '''Check keyboard ribbon and membrane''' for corrosion or cracked traces.


== Quick-Fix Flowcharts ==
== Related pages ==


=== No Video / Black Screen ===
* [[Commodore 64C]] &middot; [[Commodore 64C Troubleshooting Guide]] &middot; [[Commodore 64C Capacitor Replacement Guide]]
* Check PSU voltages โ†’ OK?
* [[Commodore 64]] &middot; [[Commodore 64 General Maintenance]] &middot; [[Commodore 64 Capacitor Replacement Guide]]
* Feel PLA/SuperPLA and VIC-II: burning hot = likely failed.
* '''[[Commodore 64 / 64C Service Manual]]''' &mdash; the source for the figures on this page
* Swap PLA โ†’ CPU โ†’ VIC-II โ†’ CIAs โ†’ ROMs.
* [[Commodore 64 Power-Supply Protector (C64 Saver)]] &middot; [[Capacitor Failure Symptoms]] &middot; [[Recommended Tools]] &middot; [[Retrobrite]]
* Still black? Probe ฯ†2 clock at CPU pin 6 and Reset at pin 3.


=== Garbled Characters / Memory Errors ===
== References ==
* Run Dead Test cartridge: count flashes to identify bad DRAM (41464).
* If only colours are wrong, suspect colour RAM (U16).
* If certain glyphs are corrupted, check character ROM (U5) and socket.


=== No Sound ===
<references />
* Confirm audio cable and TV input.
* Check SID pin 27 for output; flat-line = dead SID.
* If audio present at SID but not at output, suspect modulator electrolytic.


=== Keyboard / Joystick Dead ===
* Swap CIAs; if fixed, replace bad 6526A.
* If a row or column
[[Category:Commodore Systems]]
[[Category:Commodore Systems]]
[[Category:Maintenance Guides]]

Latest revision as of 18:32, 22 September 2026

Commodore 64C short board, assembly 250469.

The Commodore 64C short board is the simplest C64 mainboard Commodore built: two DRAMs, one combined ROM, a memory controller in place of most of the glue logic, and no 12 V regulator. It is also the revision most often described wrongly, because maintenance notes written for the long board get copied onto it. This page covers routine care specific to the 250469 E board.

The electrical figures here are taken from Commodore's own C64 / C64C Service Manual (March 1992, PN-314001-03) โ€” the parts list for PCB assembly 250469-01 and schematic 252312.[1]

For fault-finding see Commodore 64C Troubleshooting Guide; for the machine itself see Commodore 64C; for the long boards see Commodore 64 General Maintenance.

Confirm you have a short board

[edit | edit source]

Commodore's identifying factor for the E board is that the KERNAL and BASIC ROMs are combined into U4 and there is a new IC memory controller at U8. The layout page records PCB assy no. 250469, PCB no. 252311 Rev. 3.[1]

If your board has eight RAM chips and separate BASIC and KERNAL ROMs, it is a long board and the wrong page is open.

Power

[edit | edit source]

The short board takes the same 7-pin DIN supply as the bread bin: regulated +5 V DC and 9 V AC.

Power input CN7 on the E board[1]
Pin Function
1, 2, 3 Ground
4, 5 +5 V DC, regulated, from the brick — switched by SW1, filtered by C58 (100 µF 16 V)
6, 7 9 V AC — through fuse F1 (1.5 A) and line filter L1 to bridge CR2

The E board generates no +12 V rail. The 9 V AC is rectified by CR2 into C63 to make the 9 V unregulated rail, which feeds the SID supply, the cassette motor drive and the audio amplifier Q3.[1]

The SID supply is a zener, not a regulator

[edit | edit source]

On the E board the SID's Vdd comes from the 9 V unregulated rail through pass transistor Q5 and zener CR7. Commodore's note on schematic 252312 gives the zener by SID type:[1]

SID fitted CR7 Filter capacitors C70, C71 Filter capacitors C80, C81 R8
6581 12.6 V 470 pF 1800 pF Fitted
8580 9.6 V 22000 pF 2200 pF Removed

This is the thing to get right before swapping a SID. Fitting an 8580 to a board built for a 6581 puts 12.6 V on a 9 V part.

Supply checks

[edit | edit source]

Measure the brick's +5 V output before plugging it into the machine. There is no regulator on the board between it and every chip. The original supplies are potted and fail without warning. See Commodore 64 Power-Supply Protector (C64 Saver).

Go/no-go checks[1]
Signal Where Expected
+5 V 8500 CPU (U6) pin 6 (VCC). Pin 21 is GND 4.9 – 5.1 V
RESET 8500 pin 40 Low at power-up, then +5 V
Φ0 in 8500 pin 1 1.023 MHz NTSC / 0.985 MHz PAL
Φ2 out 8500 pin 39 Same frequency
VIC-II supply VIC-II (U7) pin 40 (VCC) and pin 13 (VDD) +5 V; the HMOS VIC-II needs no 12 V
SID supply SID (U9) pin 28 (VDD) 9 V with an 8580, 12 V with a 6581
SID audio out SID pin 27; audio in is pin 26 Signal present when a voice is running
+5 V (user port) CN2 pin 2; ground on pins 1 and 12 4.9 – 5.1 V
9 V AC CN2 pins 10 to 11 9 – 11 V rms

Pin 40 of the 8500 is RESET and pin 6 is Vcc. Earlier versions of this page told readers to measure +5 V at pin 40 and the clock at pin 6; both are wrong, and pin 3 is IRQ, not reset.

Chip positions

[edit | edit source]
250469-01 integrated circuits[1]
Position Part Commodore part no.
U6 8500 CPU 318012-01
U7 VIC-II, 8567 or 8562 318014-01 / 318027-01
U9 8580 SID (or 6581 on some builds) 318013-01 / 906112-01
U1, U2 6526 CIA 906108-01
U8 Memory controller, the "Super PLA" 251715-01
U4 Combined BASIC + KERNAL ROM (23128B) 251913-01
U5 Character ROM (2332C) 901225-01
U10, U11 DRAM, 64K × 4 (50464-150) 390083-07
U19 Colour RAM, 2114 901453-07 / -09
U20 8701 clock generator 251527-08 / -09
U3, U22, U23, U18, U21 74LS08, 7406/7416, 74LS14, 4066

Two corrections worth making explicitly, because both appeared on this page before:

  • The colour RAM is a separate 2114 at U19. It is not inside the memory controller.[1]
  • The character ROM is U5. U3 is a 74LS08.[1]

Capacitors

[edit | edit source]

There are no SMD tantalums on the 250469 board. Commodore's parts list is entirely through-hole: axial and radial aluminium electrolytics, ceramics and one trimmer.[1]

The reservoir is C63 (1000 µF 16 V, or 2200 µF on the France build), and the other electrolytics are C66, C43, C65, C58, C36, C44, C77 and C59. C88 and C90 on this board are ceramics, not electrolytics โ€” 220 pF and 470 pF respectively โ€” so a note telling you to replace "C88 in the modulator" is describing a long board.[1]

See Commodore 64C Capacitor Replacement Guide for the full list with Commodore part numbers. It is not repeated here, so that there is only one place on this wiki to correct.

See Capacitor Failure Symptoms for recognising a failed part.

Regular cleaning

[edit | edit source]

Case and keyboard

[edit | edit source]
  • Wipe the lighter C64C plastics with a damp microfibre cloth and a drop of mild detergent. Avoid solvents; the C64C's finish marks more easily than the bread bin's.
  • Key caps pull vertically. Clean the plungers and stems with isopropyl alcohol.
  • For yellowing see Retrobrite, and weigh the cosmetic gain against the embrittlement.
  • Lubricate the space-bar stabiliser wire with a plastic-safe grease if it sticks.

Internal

[edit | edit source]
  • Disconnect the supply and let the board sit before opening it.
  • Blow dust out with dry air; brush with a soft anti-static brush.
  • Wipe stubborn grime with isopropyl alcohol on a lint-free cloth, without flooding, and let it dry fully before reassembly.

Edge connectors and sockets

[edit | edit source]
  • Clean the cartridge, user and expansion connectors with isopropyl alcohol. Do not use an abrasive eraser โ€” the gold plating is thin.
  • Reseat the socketed ICs annually to wipe the contacts. On the E board the sockets Commodore fits are 16, 28 and 40 pin.[1]
  • Inspect for bent contacts on the cartridge and cassette ports.

Common faults on the short board

[edit | edit source]
Component Symptom First check
Power supply Anything from a dead machine to random crashes to dead chips Measure the brick's +5 V output on its own, before connecting it
Memory controller (U8) Black screen, no boot, random crashes Feel for heat; substitute a known-good part
SID (U9) No sound, distortion Check Vdd at pin 28 against the CR7 table above, then the signal at pin 27
VIC-II (U7) No video, wrong colours, vertical bars Check +5 V at pins 40 and 13; feel for heat
CIA (U1, U2) Dead keyboard, joystick or IEC Swap U1 and U2; if the fault follows the chip you have found it
DRAM (U10, U11) Random characters, memory errors Dead-test cartridge; see Commodore Test Cartridge Index
Colour RAM (U19) Correct characters, wrong colours
Character ROM (U5) Correct layout, corrupted glyphs Check the socket before the chip
8701 clock generator (U20) No clock, no display Check for activity at U20 and at 8500 pin 1

Cooling and ventilation

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The short board runs cooler than the long boards โ€” there is no 12 V regulator dissipating on it โ€” but the VIC-II, the SID and the memory controller still get warm. Small self-adhesive heatsinks are cheap insurance. Keep the top vents clear.

Preventive checklist

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  1. Test the power supply output before every session with an original brick; replace or protect it if it is out of spec.
  2. Inspect and reflow the solder joints around the power input and the switch.
  3. Reseat the socketed chips annually.
  4. Clean the cartridge and user-port connectors.
  5. Check the keyboard ribbon and membrane for cracked traces or corrosion; conductive ink repairs broken traces.
  6. Replace the electrolytics if the machine shows video noise or instability once warm โ€” after clearing the supply.

Tools

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  • Anti-static strap and mat; digital multimeter
  • Fine-tipped soldering iron, flux, braid, desoldering pump
  • Isopropyl alcohol (99 %), lint-free cloths, compressed air, soft brush
  • Contact cleaner suitable for edge connectors
  • Conductive trace pen for keyboard repairs
  • A diagnostic cartridge โ€” see Commodore Test Cartridge Index

See also Recommended Tools.

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References

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  1. โ†‘ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 Commodore Business Machines, C64 / C64C Service Manual, March 1992, PN-314001-03, hosted at Commodore 64 / 64C Service Manual. Parts list for PCB assembly 250469-01 (C64-E) and schematic 252312, giving the IC positions, the power-input wiring, the SID supply arrangement and the build differences between 6581 and 8580 fits.
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