The only suggestion I can offer is to look carefully at the components on the motherboard near the PS/2 connector. See if anything looks like it’s burnt out or anything. As I understand it, it can be bad to plug and unplug PS/2 devices while the computer is on, and that can cause damage.

danieljm wrote on 2023-07-19, 18:57:

The only suggestion I can offer is to look carefully at the components on the motherboard near the PS/2 connector. See if anything looks like it’s burnt out or anything.

Or maybe it's just the connector that went bad.

I would try cleaning the PS/2 socket with electrical contact cleaner. If that changes nothing, I would very carefully inspect the traces going to the PS/2 socket.

Like danieljim said

Maybe there's a blown fuse/coil on the mainboard near the ps2 connector, and the keyboard is now drawing power over the data lines which isn't enough to power the keyboard properly.

I've had a similar experience and I didn't notice the broken/burnt coil until I measured its continuity and upon desoldering it came off in two pieces.

Measure between pin 3 & 4 on the ps2 connecter to verify you have 5v there while the system is on.

edit: I remembered incorrectly. the coil was broken, but did still have continuity yet it was high resistance. Thus when a load like a keyboard was present, the voltage would drop and caused that strange behaviour.

I ended up disassemblingthe ps/2 ports, as result....there was nothing wrong with them, metal pins where fine and there were not corrosion.

Also i see no ruined capacitors / fuse, only very tiny chips or whatever are those, the motherboard don't recognize USB keyboards aswell, so i think it's time to toss that away.....