While I am in no way a professional repair person, I have gained some experience with repairing Commodore 64s over the last couple years doing it and thought it would be a neat idea to collect some of my findings here. The C64 is a great machine to start getting into repairing because it is incredibly well documented and there’s a lot of resources to get information from for it these days.
I’ll expand whenever I have the time.
Here’s some handy resources to get you started with C64 repair:
The Pictorial C64 Fault Guide is here: https://derbian.webs.com/c64diag/
Ray Carlsen’s troubleshooting and repair guides are here: https://personalpages.tds.net/~rcarlsen/cbm.html
You can get the .bin files for various C64 diagnostics cartridges from World of Jani (in case you want to make your own or try in an emulator): https://blog.worldofjani.com/?p=164
Here’s the GitHub with Sven’s open source diagnostics harness (for use with the C64/C128 Diagnostics Carts): https://github.com/svenpetersen1965/C64-Diagnostic-Rev.-586220-Harness