Gigabyte B250-HD3P gives me scrambled POST and hangs

[Joffer]

I've got a Gigabyte B250-HD3P and playing around with it for some amateur ethereum mining with up to five AMD RX480 cards. The stability has been on and off from time to times, but I've never experienced what I suddenly see now:

This seems to happen when I have three or more cards installed with risers, and I use the second PCIEX1_2 (second PCI-e x1 port). I can use the slot alone with one card, no problem, Windows boots.

It eventstarts win10 fine with four card as long as I don't use that slot. I would think it could be a defect motherboard, but I experienced it with another mobo of the same make and model. I thought that was defect and replaced it with another make and model, but seeing this on the second mobo can't be a "normal defect" on the mobo.

Have anyone experienced such a thing? The POST stops/hangs with this scrambled image (I've tried to replace the risers too, doesn't help)

Mobo link: https://www.gigabyte.com/Motherboard/GA-B250-HD3P-rev-10

 

[Joffer]

I'm tending to the mainboard being defect. If I boot with a gfx in the second PCI-e x1 slot Windows boots. If I add a second gfx to the main PCI-e slot for GFX (connected to the CPU) it gets scrambled. If I connect 4 gfx to all PCIe slots except the cpu-connected (main) it works. so PCIEX16_1 and PCIEX1_2 together suddenly doesn't work...
grr.. I hate unexplained hardware problems...

 

[Charlie22911]

Are the risers powered? If not that could be causing issues. Additionally a lot of those risers are of questionable quality and may themselves be responsible.

 

[Joffer]

Yes they are powered.
The thing is I've experienced it on another rig with the same motherboard too, so different risers.
I will try an older bios and also do a new check of the risers..

 

[VirtualLarry]

Does the mobo in question have a "mining mode" setting? My understanding of that setting is, it down-clocks the PCI-E slots to like 2.0 or 1.1 or something, rather than PCI-E 3.0. This helps with noise and timing margins, for using riser cards.

If your board doesn't have this feature, and isn't advertised as a "mining" board (by the mfg, not just on ebay), then possibly, you might want to switch to one that does/is.

 

[Joffer]

No dedicated mining mode. But I do/did run the PCIe ports at gen1. And latelyt tried gen2 and gen3, but as long as PCIEX1_2 is in use with some of the other ports at the same time it's borking. I haven't had time the last week to test more, had to let it go for a while to stay sane ;-)