VIC, SID, PLA are always suspect. As is any board manufactured in 1983, the hell year for long lasting C64 boards. As are MOS branded RAM chips etc. where standard parts used were in short supply, nothing like having almost every RAM chip from a different factory on the same board! Plus anything on the board from the factory already mounted in a socket, usually populated with a part Commodore knew was a bit of a dodgy stop gap shoe-in and would need replacing in future.