Commodore 64C Troubleshooting Guide: Difference between revisions
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Expand troubleshooting: death-brick PSU over-voltage (kills PLA/RAM/SID) + modern replacements; cross-link full C64 diagnostics; cited |
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* Datasette: No response may indicate CIA-1 failure or bad 4066 switch. | * Datasette: No response may indicate CIA-1 failure or bad 4066 switch. | ||
* IEC serial: No disk drive detection = CIA-2 or 7406 buffer fault | * IEC serial: No disk drive detection = CIA-2 or 7406 buffer fault | ||
== ⚠️ The power supply — the C64's biggest killer == | |||
The original Commodore "brick" power supply is the single most dangerous fault on any C64 or C64C. It has a potted, non-serviceable 5 V regulator that fails '''short''', dumping well over 5.5 V (sometimes 9 V or more) onto the 5 V rail and '''instantly frying the PLA, RAM, SID and other chips'''. A supply on the way out shows as a black or garbage screen, lock-ups, hum bars, and crashes that get worse as it warms up.<ref name="c64psu">[https://weaselsworld.com/c64-common-problems-and-how-to-fix-it/ "Commodore 64 Diagnostics and Repair"], Weasel's World; [https://www.zimmers.net/anonftp/pub/cbm/documents/repair/troubleshooting-c64.txt Ray Carlsen's C64 troubleshooting notes]; and [https://retro64.altervista.org/blog/commodore-64-repair-a-quick-guide-on-the-steps-required-to-fix-it/ Retro64]. Source for the failing "death-brick" PSU over-volting the 5 V rail and destroying the PLA/RAM/SID, and the modern replacement supplies.</ref> | |||
* '''Measure the 5 V rail (should be 4.9–5.1 V) before every session''' on an original supply, and replace anything reading above about 5.2 V. | |||
* Better, fit a '''modern regulated replacement''' (for example a Ray Carlsen "CR" adapter, an iComp/Keelog supply) or add an over-voltage protector such as the '''C64 PSU Saver''' between the brick and the machine. | |||
* The 9 V AC side feeds the SID/VIC analogue rails and the internal clock; a supply can fail on either the DC or AC side.<ref name="c64psu">[https://weaselsworld.com/c64-common-problems-and-how-to-fix-it/ "Commodore 64 Diagnostics and Repair"], Weasel's World; [https://www.zimmers.net/anonftp/pub/cbm/documents/repair/troubleshooting-c64.txt Ray Carlsen's C64 troubleshooting notes]; and [https://retro64.altervista.org/blog/commodore-64-repair-a-quick-guide-on-the-steps-required-to-fix-it/ Retro64]. Source for the failing "death-brick" PSU over-volting the 5 V rail and destroying the PLA/RAM/SID, and the modern replacement supplies.</ref> | |||
== Common faults (shared with the Commodore 64) == | |||
The C64C uses the "short" board (ASSY 250469) with the 8580 SID and a combined PLA, but its fault set is the same as the breadbin: the '''PLA is the number-one cause of a black screen''', faulty RAM gives a garbage/checkerboard screen, and the VIC-II, SID and CIAs fail in the same ways. The full component-level diagnostics — test points, the Dead Test cartridge, minimal-configuration boot and the chip-swap order — are on the '''[[Commodore 64 Troubleshooting Guide]]''' and apply directly.<ref name="c64psu">[https://weaselsworld.com/c64-common-problems-and-how-to-fix-it/ "Commodore 64 Diagnostics and Repair"], Weasel's World; [https://www.zimmers.net/anonftp/pub/cbm/documents/repair/troubleshooting-c64.txt Ray Carlsen's C64 troubleshooting notes]; and [https://retro64.altervista.org/blog/commodore-64-repair-a-quick-guide-on-the-steps-required-to-fix-it/ Retro64]. Source for the failing "death-brick" PSU over-volting the 5 V rail and destroying the PLA/RAM/SID, and the modern replacement supplies.</ref> | |||
== References == | |||
<references /> | |||
[[Category:Commodore Systems]] | [[Category:Commodore Systems]] | ||
[[Category:Troubleshooting Guides]] | [[Category:Troubleshooting Guides]] | ||