In a recent video on the More Fun Fixing It channel, a Commodore 64C from the repair pile made its way back to the workbench for a second attempt at diagnosis and repair. Originally set aside due to unclear faults, this machine’s peculiar behavior required a deeper dive to uncover and resolve the issue. Here’s a summary of the process and findings, shared with a touch of humor and insight for fellow retro computing enthusiasts.
The C64C appeared functional on startup, displaying the correct amount of free bytes and no immediate visual issues. However, when loading software or running diagnostic cartridges, subtle irregularities became apparent. For instance, certain screen elements, like text and borders, exhibited unexpected colors. Diagnostic tests pointed towards a faulty Color RAM (chip U19), but further confirmation was needed.
Running several diagnostic tools, including the original and updated versions of the “Dez Test” diagnostic software, confirmed the Color RAM was the culprit. Interestingly, an early version of the test software itself had a minor bug that led to incorrect address reporting, prompting a collaboration with its creator, Matt Desmond, who promptly fixed the issue and provided updated code. This teamwork highlighted the benefits of sharing findings within the retro-computing community.