My good friend gave this 486 PC couple of months ago. When he gave it to me it was working fine, but i haven't tested it as i wanted to upgrade it to 486DX2. So i modded the board to make ordinary DX2 work in 487 socket (B14 to ground with 33ohm resistor). Unfortunately after i did the mod it wont post at all, so i undid the mod and it wont post either. PSU is starting it gives me a blink of leds on the keyboard and nothing, even power on led is not working and i have no beeps from the speaker.
Inspected everything, reflew all the suspicious solder points, reseated BIOS chip as well as read it in the eprom programmer, wiped it with UV-C eprom eraser and programed BIOS again, without any luck, the board just wont post. CPU is getting warm both SX without mod and DX2 with mod applied, when mod is applied then SX is cold.
Next thing i did is to measure voltages while PC was on, PSU has non-standard connector for the board, and it gave readings +5.04V +11.83 -12.08 which is fine but i have two more wires coming in from the PSU. RST and STB readings are+0.35V on RST and 0.28V on STB.

Anybody has any ideas where to look.