[GRudolf94]

Greetings

So, by the looks of it, I would guess that your board either has a shorted tantalum capacitor, or something else making the PSU go into short circuit protection. Either that, or something is out of spec on the PSU, and the I2 has a power_good signal that cuts out the PS_ON signal if the PSU doesn't detect voltages to be in the proper range. Your pinout description mostly matches what I found when probing my IP28 with a multimeter (my system came without a PSU). Whatever I found is here: https://forums.irixnet.org/thread-493.html

Does your PSU have colorful wires? The 3.73V signal intrigues me. Could that be the PS_ON signal?