It's the Octek Jaguar V motherboard, I can't see anyhing wrong, mouse only worked once by luck. One of the times i removed and installed the controller card. The PSU is good, checked the -12V rail but it's not in the serial port pins. I've tried different controllers and another isa slot (second one) instead of third. There was a bit of barrel battery corrosion but it was very minor, only on pins of one chip. I haven't looked at the back of the board. The power connector is fine.
https://imgur.com/a/rdqAcOD