Commodore 64 General Maintenance - Revision history

Josh: Set 1 table to 70% width so it sits next to the image

2026-10-06T09:35:09Z

Set 1 table to 70% width so it sits next to the image

← Older revision		Revision as of 10:35, 6 October 2026
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	The assembly number is printed on the board. 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 printed on the board. Commodore's identification table:<ref name="smid">''Service Manual C64/C64C'' (1992), "C64 Board Identification" and "C64C Board Identification", p. 17.</ref>

	{\| class="wikitable styled-table" style="width:~~100~~%; text-align:left;"		{\| class="wikitable styled-table" style="width:70%; text-align:left;"
	\|+'''C64 and C64C board assemblies'''		\|+'''C64 and C64C board assemblies'''
	! Version !! Identifying factor (Commodore) !! PCB assembly !! Schematic		! Version !! Identifying factor (Commodore) !! PCB assembly !! Schematic

Josh: Tolerance note: cite diagnostic manual 10 %

2026-10-01T08:52:23Z

Tolerance note: cite diagnostic manual 10 %

← Older revision		Revision as of 09:52, 1 October 2026
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	\|}		\|}

	Commodore fitted Motorola MC7812CT and MC7805CT regulators~~; the voltage~~ limits above are the generic 78xx datasheet figures~~, as~~ Commodore's manual ~~gives none~~.<ref name="~~smps~~" />		Commodore fitted Motorola MC7812CT and MC7805CT regulators. The limits above are the generic 78xx datasheet figures; Commodore's diagnostic manual allows 10 % on all its readings.<ref name="dm" />

	The reset pulse comes from U20, an LM556 timer wired as a one-shot. Commodore gives the pulse width as 1.1 × R34 × C24, about half a second, with the timer's output on pin 9 inverted by U8 to drive the active-low reset.<ref name="smrst" />		The reset pulse comes from U20, an LM556 timer wired as a one-shot. Commodore gives the pulse width as 1.1 × R34 × C24, about half a second, with the timer's output on pin 9 inverted by U8 to drive the active-low reset.<ref name="smrst" />

Josh: Add Commodore diagnostic manual supply figures (9-12 V AC at CN7, VIC-II supply pins, reset timing)

2026-10-01T08:51:34Z

Add Commodore diagnostic manual supply figures (9-12 V AC at CN7, VIC-II supply pins, reset timing)

← Older revision		Revision as of 09:51, 1 October 2026
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	\|}		\|}

	On a running machine, the user port carries +5 V on pin 2 (ground on pins 1, 12, A and N) and the 9 V AC on pins 10 and 11.<ref name="c64wup">C64-Wiki, [https://www.c64-wiki.com/wiki/User_Port "User Port"], pin assignment table. Retrieved 2026-10-01.</ref><ref name="smps" /> Measure the AC between pins 10 and 11. The C64-Wiki gives about 8.1 V AC as the lowest the machine will run on, and notes that the transformer reads higher unloaded than loaded.<ref name="c64wps" />		On a running machine, the user port carries +5 V on pin 2 (ground on pins 1, 12, A and N) and the 9 V AC on pins 10 and 11.<ref name="c64wup">C64-Wiki, [https://www.c64-wiki.com/wiki/User_Port "User Port"], pin assignment table. Retrieved 2026-10-01.</ref><ref name="smps" /> Measure the AC between pins 10 and 11. Commodore's diagnostic manual expects 9 to 12 V AC at CN7 pins 6 and 7 and +5 V at CN7 pin 5, all within 10 %.<ref name="dm">Commodore Business Machines, ''C64 Diagnostic Instruction and Troubleshooting Manual, Assembly #326070-01'', 1992, Section 2, pp. 2-1, 2-3 and 2-4, hosted at [[Commodore 64 Diagnostic Instruction and Troubleshooting Manual (326070-01)]].</ref> The C64-Wiki gives about 8.1 V AC as the lowest the machine will run on, and notes that the transformer reads higher unloaded than loaded.<ref name="c64wps" />

	Some original supplies can be opened and repaired; others are glued shut and potted.<ref name="c64wps" /> The primary side of any of them runs at mains voltage. Unplug the supply from the wall before opening it. For an over-voltage cut-out see [[Commodore 64 Power-Supply Protector (C64 Saver)]].		Some original supplies can be opened and repaired; others are glued shut and potted.<ref name="c64wps" /> The primary side of any of them runs at mains voltage. Unplug the supply from the wall before opening it. For an over-voltage cut-out see [[Commodore 64 Power-Supply Protector (C64 Saver)]].
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	\| +5 V \|\| 6510 (U7) pin 6; ground is pin 21<ref name="smpin">''Service Manual C64/C64C'' (1992), pin assignments for U7 6510 and U17 PLA, p. 27.</ref> \|\| Same as the supply reading above		\| +5 V \|\| 6510 (U7) pin 6; ground is pin 21<ref name="smpin">''Service Manual C64/C64C'' (1992), pin assignments for U7 6510 and U17 PLA, p. 27.</ref> \|\| Same as the supply reading above
	\|-		\|-
	\| RESET \|\| 6510 pin 40<ref name="smpin" /> \|\| ~~Low for~~ about 0.5 s ~~after power-on~~, ~~then high~~<ref name="smrst">''Service Manual C64/C64C'' (1992), Circuit Theory, "Reset Logic Circuits", p. 5.</ref>		\| RESET \|\| 6510 pin 40<ref name="smpin" /> \|\| 0 V at power-on, rising to +5 V; about 0.5 s in the service manual, about 1 s in the diagnostic manual<ref name="smrst">''Service Manual C64/C64C'' (1992), Circuit Theory, "Reset Logic Circuits", p. 5.</ref><ref name="dm" />
	\|-		\|-
	\| Phase 0 clock in \|\| 6510 pin 1<ref name="smpin" /> \|\| About 1.02 MHz (NTSC) or 0.985 MHz (PAL)<ref name="smclk">''Service Manual C64/C64C'' (1992), Circuit Theory, "The C64 Clock Circuits", p. 6; dot clock frequencies in the notes to schematic 252312, p. 42.</ref>		\| Phase 0 clock in \|\| 6510 pin 1<ref name="smpin" /> \|\| About 1.02 MHz (NTSC) or 0.985 MHz (PAL)<ref name="smclk">''Service Manual C64/C64C'' (1992), Circuit Theory, "The C64 Clock Circuits", p. 6; dot clock frequencies in the notes to schematic 252312, p. 42.</ref>
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	\| Phase 2 clock out \|\| 6510 pin 39<ref name="smpin" /> \|\| Same frequency		\| Phase 2 clock out \|\| 6510 pin 39<ref name="smpin" /> \|\| Same frequency
	\|-		\|-
	\| +12 V \|\| VR1 output; SID pin 28 (VDD) \|\| 11.5-12.5 V (7812 limits)<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 (7805) and 6.7 (7812), output voltage at TJ = 25 °C.</ref>		\| +12 V \|\| VR1 output; VIC-II (U19) pin 13; SID pin 28 (VDD) \|\| 11.5-12.5 V (7812 limits)<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 (7805) and 6.7 (7812), output voltage at TJ = 25 °C.</ref>
	\|-		\|-
	\| +5 V CAN \|\| VR2 output \|\| 4.8-5.2 V (7805 limits)<ref name="ti78" />		\| +5 V CAN \|\| VR2 output; VIC-II (U19) pin 40 \|\| 4.8-5.2 V (7805 limits)<ref name="ti78" />
	\|-		\|-
	\| SID audio \|\| Pin 27 out, pin 26 in<ref name="smav">''Service Manual C64/C64C'' (1992), Circuit Theory, "8 Pin Video and Audio Output Circuits", p. 10.</ref> \|\| Signal while a voice is playing		\| SID audio \|\| Pin 27 out, pin 26 in<ref name="smav">''Service Manual C64/C64C'' (1992), Circuit Theory, "8 Pin Video and Audio Output Circuits", p. 10.</ref> \|\| Signal while a voice is playing

Josh: Re-cite to service manual pages; replace invented tolerances (4.9-5.1 V, 9-11 V AC) with C64-Wiki and 78xx datasheet figures; drop invented symptom column, annual reseat interval, heatsink and Retrobrite advice; fix C90 role; remove self-reference and bold

2026-10-01T08:45:01Z

Re-cite to service manual pages; replace invented tolerances (4.9-5.1 V, 9-11 V AC) with C64-Wiki and 78xx datasheet figures; drop invented symptom column, annual reseat interval, heatsink and Retrobrite advice; fix C90 role; remove self-reference and bold

Show changes

Josh: Correct the VIC-II row to what Commodore's parts lists actually print; the 6569 designation is not in this manual

2026-09-22T17:34:06Z

Correct the VIC-II row to what Commodore's parts lists actually print; the 6569 designation is not in this manual

← Older revision		Revision as of 18:34, 22 September 2026
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	\| CPU \|\| '''U7''' \|\| 6510, 906107-01 \|\| Blank screen; cursor locks up; cassette motor faults		\| CPU \|\| '''U7''' \|\| 6510, 906107-01 \|\| Blank screen; cursor locks up; cassette motor faults
	\|-		\|-
	\| VIC-II \|\| '''U19''' \|\| 6567 (NTSC~~) / 6569 (PAL)~~, 906109-04 \|\| Blank screen, graphic characters instead of letters		\| VIC-II \|\| '''U19''' \|\| 6567, Commodore 906109-04 (the B-3 list marks it "VIC NTSC", 906109-01) \|\| Blank screen, graphic characters instead of letters
	\|-		\|-
	\| SID \|\| '''U18''' \|\| 6581, 906112-01 \|\| No sound		\| SID \|\| '''U18''' \|\| 6581, 906112-01 \|\| No sound

Josh: Rebuild from the C64/C64C Service Manual: 6510 +5V is pin 6 not pin 40, RESET is pin 40 not pin 3, phi2 is pin 39 not pin 2; SID audio out is pin 27 not pin 28; 9VAC is user-port pins 10-11 not 10-12; power DIN pin 1 is ground not +5V; capacitor values (1000uF/16V, 470uF/25V, two 220uF, 250469-05 SMD tantalums) were wrong and are removed in favour of the capacitor guide; 41464 is 256kbit not 128kbit; board table replaced with Commodore's own including B-2 250441-01; emoji heading removed; Unv...

2026-09-22T17:32:37Z

Rebuild from the C64/C64C Service Manual: 6510 +5V is pin 6 not pin 40, RESET is pin 40 not pin 3, phi2 is pin 39 not pin 2; SID audio out is pin 27 not pin 28; 9VAC is user-port pins 10-11 not 10-12; power DIN pin 1 is ground not +5V; capacitor values (1000uF/16V, 470uF/25V, two 220uF, 250469-05 SMD tantalums) were wrong and are removed in favour of the capacitor guide; 41464 is 256kbit not 128kbit; board table replaced with Commodore's own including B-2 250441-01; emoji heading removed; Unv...

Show changes

Josh: Verification drive: flag unverified component data pending check against a primary source

2026-09-21T20:50:54Z

Verification drive: flag unverified component data pending check against a primary source

← Older revision		Revision as of 21:50, 21 September 2026
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			{{Unverified data}}
	<templatestyles src="Template:StyledTable/styles.css" />		<templatestyles src="Template:StyledTable/styles.css" />
	[[File:C64 ASSY NO 250425 motherboard 1984.jpg\|thumb\|359x359px\|Commodore 64 (250425) Motherboard]]		[[File:C64 ASSY NO 250425 motherboard 1984.jpg\|thumb\|359x359px\|Commodore 64 (250425) Motherboard]]

Josh at 07:36, 12 May 2025

2025-05-12T07:36:19Z

← Older revision		Revision as of 08:36, 12 May 2025
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	<templatestyles src="Template:StyledTable/styles.css" />		<templatestyles src="Template:StyledTable/styles.css" />
	[[File:C64 ASSY NO 250425 motherboard 1984.jpg\|thumb\|359x359px\|Commodore 64 (250425) Motherboard]]		[[File:C64 ASSY NO 250425 motherboard 1984.jpg\|thumb\|359x359px\|Commodore 64 (250425) Motherboard]]
	The ~~legendary~~ '''Commodore 64''' (C-64, C64 C, “bread bin”, 64C, Aldi C64, SX-64) is now 40-plus years old. Aging electrolytic capacitors, brittle plastics, and the infamous “death‐brick” PSU all put these machines at risk.		The '''Commodore 64''' (C-64, C64 C, “bread bin”, 64C, Aldi C64, SX-64) is now 40-plus years old. Aging electrolytic capacitors, brittle plastics, and the infamous “death‐brick” PSU all put these machines at risk.

	This page collects '''best-practice hardware care''', preventive service, fault-pre-emption, and periodic checks for '''every board revision from 1982 ASSY 250407 to the late 250469-05 short board'''. Follow the sections below to keep a C-64 healthy for the next four decades.		This page collects '''best-practice hardware care''', preventive service, fault-pre-emption, and periodic checks for '''every board revision from 1982 ASSY 250407 to the late 250469-05 short board'''. Follow the sections below to keep a C-64 healthy for the next four decades.

	== 🔍 Identify Your Board Revision ==		== Identify Your Board Revision ==
	{\| class="wikitable styled-table" style="width:100%; text-align:center;"		{\| class="wikitable styled-table" style="width:100%; text-align:center;"
	\|+'''C-64 Motherboard Generations'''		\|+'''C-64 Motherboard Generations'''
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	''Find the '''ASSY''' number silkscreened near the cartridge port or RF modulator.''		''Find the '''ASSY''' number silkscreened near the cartridge port or RF modulator.''

	== 🧼 Regular Cleaning ==		== Regular Cleaning ==
	=== Case & Keyboard ===		=== Case & Keyboard ===
	* Wipe ABS plastic with a '''damp micro-fiber cloth & mild dish-soap'''.		* Wipe ABS plastic with a '''damp micro-fiber cloth & mild dish-soap'''.
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	* Re-seat every socketed IC to wipe oxidised contacts.		* Re-seat every socketed IC to wipe oxidised contacts.

	== 🔋 Power Supply: The “Death Brick” ==		== Power Supply: The “Death Brick” ==
	[[File:Internals of C64 Power Supply (8595594936).jpg\|thumb\|Commodore 64 Power Supply\|250x250px]]		[[File:Internals of C64 Power Supply (8595594936).jpg\|thumb\|Commodore 64 Power Supply\|250x250px]]
	Original Commodore linear bricks often drift above '''5.5 V DC''', frying PLA, DRAM and SID.		Original Commodore linear bricks often drift above '''5.5 V DC''', frying PLA, DRAM and SID.
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	'''Safe replacements:''' modern switch-mode “C64RMK2”, Ray Carlsen’s CR adapter, or over-voltage-protected DIY bricks.		'''Safe replacements:''' modern switch-mode “C64RMK2”, Ray Carlsen’s CR adapter, or over-voltage-protected DIY bricks.

	== 💣 Capacitor Health ==		== Capacitor Health ==
	C-64 boards generally fare better than Amigas, but '''filter cans in the RF modulator''' and '''5 V/12 V regulators''' dry out.		C-64 boards generally fare better than Amigas, but '''filter cans in the RF modulator''' and '''5 V/12 V regulators''' dry out.
	Early long boards: replace the '''1000 µF / 16 V +5 V filter, 470 µF / 25 V +12 V''', and the two 220 µF caps in the cassette/9 VAC rectifier path.		Early long boards: replace the '''1000 µF / 16 V +5 V filter, 470 µF / 25 V +12 V''', and the two 220 µF caps in the cassette/9 VAC rectifier path.
	Short board 250469-05 uses SMD tantalums—rarely fail, but the modulator still contains 22 µF / 16 V electrolytics. See [[Commodore 64 Capacitor Replacement Guide]] for more detailed replacement information.		Short board 250469-05 uses SMD tantalums—rarely fail, but the modulator still contains 22 µF / 16 V electrolytics. See [[Commodore 64 Capacitor Replacement Guide]] for more detailed replacement information.

	== ⚠️ Known Failure-Prone ICs ==		== Known Failure-Prone ICs ==
	{\| class="wikitable styled-table" style="width:100%; text-align:center;"		{\| class="wikitable styled-table" style="width:100%; text-align:center;"
	\|+'''C-64 Common Chip Failures'''		\|+'''C-64 Common Chip Failures'''
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	\|}		\|}

	== 🧰 Essential Tools ==		== Essential Tools ==
	* ESD wrist-strap & soft bristle brush		* ESD wrist-strap & soft bristle brush
	* Digital multimeter (check PSU every session)		* Digital multimeter (check PSU every session)
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	* Freeze spray or hot-air pencil for thermal fault hunts		* Freeze spray or hot-air pencil for thermal fault hunts

	== 📝 Preventive Maintenance Checklist ==		== Preventive Maintenance Checklist ==
	# '''Test PSU''' – verify +5 V & 9 VAC before connecting computer.		# '''Test PSU''' – verify +5 V & 9 VAC before connecting computer.
	# '''Inspect regulators''' 7805 / 7812 for cracked solder joints; re-flow if dull.		# '''Inspect regulators''' 7805 / 7812 for cracked solder joints; re-flow if dull.
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	# '''Ventilation''' – leave 2 cm clearance above vents; consider modern transparent top-shell or fan for hot climates.		# '''Ventilation''' – leave 2 cm clearance above vents; consider modern transparent top-shell or fan for hot climates.

	== 🛠️ Quick-Fix Flowcharts ==		== Quick-Fix Flowcharts ==
	=== 🖥️ No Video / Black Screen ===		=== No Video / Black Screen ===
	* Check PSU rails → OK?		* Check PSU rails → OK?
	* Feel PLA & VIC: burning hot = replace.		* Feel PLA & VIC: burning hot = replace.
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	* Still black? probe φ2 clock & Reset; if missing, suspect 8701 clock generator or bad crystal.		* Still black? probe φ2 clock & Reset; if missing, suspect 8701 clock generator or bad crystal.

	=== 🎨 Garbled Characters / Checkerboard ===		=== Garbled Characters / Checkerboard ===
	* Run Dead Test cart: code flashes DRAM bank; count flashes to identify bad 4164.		* Run Dead Test cart: code flashes DRAM bank; count flashes to identify bad 4164.
	* If only colors wrong → replace 2114 color RAM.		* If only colors wrong → replace 2114 color RAM.
	* If only certain glyphs wrong → character ROM (901225-01) socket issue.		* If only certain glyphs wrong → character ROM (901225-01) socket issue.

	=== 🔊 No Sound ===		=== No Sound ===
	* Confirm volume & cable → check SID pin 27 audio-out with scope; flat-line = dead SID.		* Confirm volume & cable → check SID pin 27 audio-out with scope; flat-line = dead SID.
	* Audio present before modulator but silent on TV = RF modulator electrolytic or bad audio-mix resistor.		* Audio present before modulator but silent on TV = RF modulator electrolytic or bad audio-mix resistor.

	=== ⌨️ Keyboard / Joystick Dead ===		=== Keyboard / Joystick Dead ===
	* Swap CIAs; if fixed, replace bad 6526.		* Swap CIAs; if fixed, replace bad 6526.
	* If row/column missing → inspect keyboard ribbon; repair broken trace with conductive ink.		* If row/column missing → inspect keyboard ribbon; repair broken trace with conductive ink.

	[[Category:Commodore Systems]]		[[Category:Commodore Systems]]
	[[Category:~~Commodore~~ Maintenance Guides]]		[[Category:Maintenance Guides]]

Josh: /* 🔋 Power Supply: The “Death Brick” */

2025-04-24T09:01:36Z

🔋 Power Supply: The “Death Brick”

← Older revision		Revision as of 10:01, 24 April 2025
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	== 🔋 Power Supply: The “Death Brick” ==		== 🔋 Power Supply: The “Death Brick” ==
	[[File:Internals of C64 Power Supply (8595594936).jpg\|thumb\|Commodore 64 Power Supply]]		[[File:Internals of C64 Power Supply (8595594936).jpg\|thumb\|Commodore 64 Power Supply\|250x250px]]
	Original Commodore linear bricks often drift above '''5.5 V DC''', frying PLA, DRAM and SID.		Original Commodore linear bricks often drift above '''5.5 V DC''', frying PLA, DRAM and SID.
	{\| class="wikitable styled-table" style="width:70%;"		{\| class="wikitable styled-table" style="width:70%;"

Josh: /* 🔋 Power Supply: The “Death Brick” */

2025-04-23T19:42:16Z

🔋 Power Supply: The “Death Brick”

← Older revision		Revision as of 20:42, 23 April 2025
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	== 🔋 Power Supply: The “Death Brick” ==		== 🔋 Power Supply: The “Death Brick” ==
			[[File:Internals of C64 Power Supply (8595594936).jpg\|thumb\|Commodore 64 Power Supply]]
	Original Commodore linear bricks often drift above '''5.5 V DC''', frying PLA, DRAM and SID.		Original Commodore linear bricks often drift above '''5.5 V DC''', frying PLA, DRAM and SID.
	{\| class="wikitable styled-table" style="width:70%;"		{\| class="wikitable styled-table" style="width:70%;"