I don't know a single vintage enthusiast who doesn't have at least a few Commodore 64s hanging around, but the reason they almost always have more than one is that by now, the Commodore 64 isn't exactly the most reliable machine ever built. Poor storage and poor maintenance over the machine's life are the general culprits I've seen, especially with all those nice exposed edge connectors...
Why start a topic about it though? Because I have five Commodore 64s and none of them work. One is a whole lot closer than the others to functional though and after a careful strip and check operation the board is in significantly better condition than the others. It also boots... sometimes. Now I've run through Project 64's C64 diagnostics and tried a few of the fixes, specifically the 6510 and the 6567 with others from my fallen comrades - the fault appears to have persisted past those chips.
So the fault is basically that when it powers up, I either get a black screen, the BASIC display with no text, garbled text or sometimes all there. IF it gets to that point, I either get half the keyboard not working, total freeze or it works properly - if it does work properly, it will load software. I DID manage to get it to load and start GEOS, although once it did that it froze up immediately. I haven't been able to get anything to load prior or since.
Everything I've read is starting to point at the CIAs. If anyone else has anything to glean, let me know... I don't really want to have to desolder a pair of CIAs from one of the donors if I don't have to. Good thing the donor board is fully socketed!