Ferdinand Keil's

electronic notes

Nov 16, 2019

How not to replace your BIOS EEPROM

One of my PCs recently started freezing out of nowhere. It would freeze in the BIOS, during booting, while running. When frozen it would react to the power button, which made me curious. After ruling out all peripherals internal and external by disconnecting them, reapplying thermal paste to the CPU, memchecking and trying a differnt power supply I ran out of options. The final suspect was the mainboard. Before giving up I wanted to try and swap the BIOS EEPROM.

What made me suspicous of the BIOS EEPROM you ask? Well, every time this PC boots it programs the BIOS to wake it up during the night to run some backups. I do not know whether this setting is written to the EEPROM or the RTC RAM, but writing it often could potentially damage the EEPROM's flash.

So I found another EEPROM in the junk bin, got myself a CH341A-based flash programmer and off I went. Or so I thought. The EEPROM I found was a different size (8 MB vs. 1 MB for the old EEPROM). Of course flashrom did complain about that, but by padding the ROM image I could get it to program the larger EEPROM anyway.

But to no avail. The PC would not boot from this EEPROM. So, turns out you can't swap EEPROM ICs willy nilly.