// 05/09/2026 // by Elder0010
This machine belonged to the Raoul’s loot. It was completely dead at boot. I measured the output voltages from the external brick and verified that the power supply was functioning correctly. However, the internal converter was not providing the necessary voltages to the motherboard, suggesting a fault within the internal power circuitry. Some capacitors were out of spec, and needed replacement.
I tested the power supply in isolation and the output voltages were ok. I even tested it with a test load around 0.8A (a couple of old IDE hdd) and everything remained stable.
But, as soon as I connected it to the motherboard, the voltages dropped and the machine remained dead! I began troubleshooting the motherboard: fuse was ok, and no visible damage or burnt components were found. I couldn’t find a short circuit either.
I suspected that the oard was draining more current than the power supply could provide, causing the voltage drop and preventing the machine from booting. So i tested it with a bench power supply to monitor the current draw and voltage stability, it booted (with a garbage screen), even tho the amperage was higher than expected (1.5A moreless).
After a lot of trial and error, isolating voltages on the motherboard and without finding any obvious faults, I decided to move forward with the motherboard repair (using the bench power supply).
After replacing 2X 4164 Rams, the machine booted successfully, and I noticed that the amperage draw lowered to 0.9A! I then reconnected the original internal power supply converter and the machine continued to operate normally.
Some keys weren’t working, but it was about to recrimp the keyboard connector, which resolved the issue.
The disk drive was in excellent condition - I gave it just a quick cleaning and lubrication, and it worked perfectly. The drive activity led was broken.
The keyboard protection membrane was almost destroyed (a common issue on the IIc), so I removed it.
