Sometimes the smallest things cause the worst of all troubles...
When building Thor IV I had to deal with various forms of misbehaviour after system power down:
- BIOS settings being reset randomly
- RTC jumping to the year 2300
- system requiring multiple POSTs to detect video
Most of them were gone with the final parts constellation (AORUS Xtreme X570 and RTX 2080SUPER) but after a couple of months in deceptive peace the BIOS issues returned.
I was already about to resign on this matter when I stumbled upon a post on Reddit about the DisplayPort Pin 20 Issue which I had not heard of yet.
Without rehasing it all again here is the TL;DR:
- DP Pin 20 (
DP_PWR) is specified to supply power from one side at 3.3V for active in-cable components like powered adaptors
- cheap cables violate the VESA specification and simply route that pin through both ends
- this can cause massive electrical issues when such a cable is used to connect a monitor to a graphics card as both may try to supply power
In my case (having exactly such a cable) my monitor was 'backdriving' my system, feeding power through my graphics card over PCIe to the motherboard, which clearly didn't like it.
Replacing the cable with a proper one that does not connect
DP_PWR fixed my
BIOS reset issue.