Lee from More Fun Fixing It is back with another challenge: a blue screen Commodore 64 repair. This machine came in with suspicious evidence of earlier fixes, including clipped ROM legs and a mismatched CIA chip. With a cautious inspection complete, Lee begins the familiar cycle of testing the CIA, ROMs, CPU, and PLA.
The first checks look promising. Voltages across the board measure correctly, and reset signals appear healthy. Yet the machine stubbornly refuses to boot. At this stage, Lee focuses on the CIAs, suspecting the replacement history might hide trouble. Testing reveals strange voltage behavior on pin nine of one CIA. The signal should sit high, but instead floats in an unstable range. That finding points squarely at the chip.
After careful desoldering and socket work, Lee tests replacements. The system shows signs of life but still will not boot cleanly. The investigation moves toward the ROMs, which display odd repair work from previous attempts. Both the BASIC and kernel ROMs become suspects. Swapping them in and out does not resolve the crash, though. Frustration builds as every logical step seems to stall.
Then comes the breakthrough. With diagnostic cartridges inserted, the system runs, but normal booting fails. That contradiction suggests the problem lies deeper. Lee shifts attention to the VIC-II graphics chip, which had not been considered a strong suspect. Once swapped, the Commodore 64 springs back to life with a stable picture and working boot sequence.
The outcome is bittersweet. The machine now works, but with a faulty VIC-II, CIA, and SID chip, it is close to being a parts donor. Yet the repair teaches an important lesson: never rule out unexpected components, even when symptoms seem to point elsewhere.
This episode of blue screen Commodore 64 repair demonstrates the persistence needed when common failures are not the cause. For anyone interested in retro hardware troubleshooting, this is a fascinating and unpredictable watch.
