Question Start Up Issue - Booting only by quickly switching power supply

Feb 21, 2021
Hello there - I have had the following issue with my computer build for several months: Quite a while back the Power button on my case got busted, but the electronic button it pushed on the case underneath still worked, so I could still start my system by pressing it with a pen or a screwdriver. Eventually that stopped working, but I could still switch on my computer by quickly switching my power supply off and on again. This then degraded to only being possible while I held the power switch on the case with a pen or screwdriver as well, so my explanation was that it was finally time to get a new case and stop with the acrobatics. So now I transferred my whole build to a new case and the issue sort-of persists. I also replaced the CMOS battery while doing that because that had died in the meantime, the system clock always resetted if I took the computer off power (my build is now five years old).

I still can not turn on the computer other than by quickly using the Power Supply Switch, interestingly on test boot without monitor I could turn the system back off with the power button on the new case. When I power on by quickly toggling the Power Supply in the back everything works without issue. My suspicion is obviously that the power switch on the motherboard is fried - but is there anything else I might have overlooked? And what do I do if it's the motherboards power supply? Is there a simple way to fix it or do I have to replace the whole board?

System components:
ASUS Z170-A Motherboard
Intel i5 6600k
Alpenföhn CPU Cooler
Geforce GTX 970 Graphics
2x4 gb DDR-4 Kingston 2667 Mhz
Power Supply Seasonic G-Series G-550 Modular 80+ Gold 550 Watts