I know following up your own request is kinda taboo, but I should have shared more information... I am guessing that the problem is with the Color RAM (SRAM) in slot U6. This model of C64 has socketed components, but I am not sure U6 is one of these. The other possible issue is PLA U17. As the problem never goes away, perhaps it is more than this. Is there a good vendor to get replacements this late in the game? Kevin