MOS chips are notorious among system restorers even today. Commodore's power supply design that made the most common failure mode one that increased the voltag

MOS chips are notorious among system restorers even today. Commodore's power supply design that made the most common failure mode one that increased the voltage output so it fried the attached machine is another stellar design decision. That said, Commodore sold a ton of hardware in the 80s. There is a cottage industry around getting C64s up and running again, and since they're so plentiful and well known it's almost always possible to fix them. There are replacement chips for everything on the board, even the weirdo custom stuff like the PLAs. Everything on the C64 has been reverse engineered and well documented.