Hi folks !

As I recently received a bunch of old CPUs (in which there was an am5x86 and an am486DX4 with write-back L1 cache), I wanted to upgrade the intel 486 DX2-66 that I did put on that board. Unfortunately, while the DX2 seems to work perfectly (I don't use that computer that often at the moment), the DX4 chip does'nt POST at all. Even the keyboard does'nt receive a reset signal. I triple-checked the jumpers, tried other 3.3v CPUs and I came to the conclusion that the VRM is probably dead as it, and the CPU doesn't heat up. It's fine when using a 5V CPU, but when the board is set in "3.3v CPU" mode, it acts as it's dead.

Why is it dead ? Well ... when I got that board a few years ago, I still knew nothing about 486s and I was curious to see what was the cpu. It was an am486 DX2-80. But unfortunately when I put it back, I put it in a completely wrong way (180°). Since that was the only 3.3V board I had, I thought that I killed that poor 486, but now that I found out this (the two DX4 are completely fine in my AP43), I really think that the VRM died in that process. I hope that actually the am486 DX2-80 is fine as it's not the most common chip ever (but of course not the rarest) but I don't know for now.

Unfortunately, when I removed the heatsink, I could not see any markings that would tell me what is exactly that VRM ... Do you have any ideas of which VRM is used on this board ? Is it the same as other 486 boards or is it different ? Could it be a fuse that blew up instead (even though there is no burn remains anywhere on that board)

Thanks for help ^^