Have you connected any peripherals? Disconnect everything and remove any cards you’ve installed except for the graphics card and try again.

Thanks I will try that

I'm not sure about 386 boards but I've seen simple resistor/capacitor reset circuits before. Usually the reset signal needs to be held for a certain amount of time to ensure the processor is fully reset. Or instable power due to bad filter caps. Anything looking suspicious? Caps can be bad without leaking or bulging, so not seing anything isn't a clear "all good" signal unfortunately. Did the RTC battery leak (if any)?

Does your mainboard have a jumper to select between the "power good signal" of the PSU or an onboard circuit?

Thanks all. Will check the caps etc . No no jumper for that.

Again thanks. You helped out again: I figured out it’s my network card (3com 3c905b-c in non-pnp mode with xt-ide rom).

I will now dive deeper into certain config setting. I assume it’s related to the xt ide bios but let’s see.

Again thanks so far. Keep you updated

Too early. Issue still is there. Sorry

So finally I could really find a specific card being responsible for the behavior. I tested all. Issue didn’t occur all the time just right now. Maybe because it’s very warm in the room today. Haha sorry but this might give a root cause within the electric field anyway. It also seems to be more related to the number of cards installed. Pls note that I had same issues with another PS

As far as I could see I didn’t see a noteable cap or sth. But that’s just my view 😒

This has a dying PSU´s fingerprints all over it. Have you already tried with a different (known 100% working) PSU??

Hm I tried with another PSU indeed. But damn I don’t remember whether it was working there or not. Nor do I not know whether that other psu was 100% ok. But thanks I will keep an eye on a new ps.