First post, by EnergyStar
Motherboard started with "keyboard error" and "CMOS checksum error" errors. The keyboard didn't work. Not every time the motherboard started, sometimes it crashed with the C7 error code.
- I changed electrolytes
- I checked the keyboard socket, corrected the solder
- I replaced four SMD capacitors next to the keyboard DIN connector
- I was programming the BIOS on three different CMOS chips.
- I changed the processor
- I tried on different RAM chips in different slots.
I had some brand new Dallas DS12C887 + chips, so I decided to replace it. The board stopped working on the new chip, moreover I found information that the new chip should be activated with a simple program, so I re-soldered the old chip. After this treatment, the motherboard has not started even once, it stops at the C7 error.
I put flux and fresh tin on the lower chipset - no effect. I did the same with a few other smaller chips. I tried to push them down. I desoldered and re-soldered the UMC 8667 chip that supplies voltage to the COM ports. Tried reprogramming the BIOS on different chips.
Most of the integrated circuits are cool, the CPU gets slightly hotter locally.
What else could I do?