First pc build - system sends signal with 2 gpus but not 3

Nov 12, 2018
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Hey guys, first post here! I'm setting up my first build and I have this issue:
The pc has 2 zotac minis (pcie 1 &4) and a sapphire radeon (pcie 2).
They're not connected with sli or crossfire, the zotacs are for deep learning so looks like they should work as they are.
Sapphire doesn't need/have cable power while the other two are connected with a single cable to my aerocool psu (850W).
Only sapphire is connected to monitor via dvi.
The system can't send signal to the monitor when all 3 are on the mobo but I managed to view the bios screen when I removed the gpu (zotac) on pcie 1.
Putting it back in, no signal.

Is it because the system checks pcie 1 first before moving on to the next?
I think I've connected that gpu to the monitor before and there was no signal either but I'll double check.
Btw the cpu is a threadripper with 64 lanes so that's most likely not an issue (all pcie lanes combined are 40 plus an m.2)
 
Nov 12, 2018
2
0
10


Mobo is asrock taichi x399
Cpu threadripper 1900x
2 zotac mini gtx 1070
Sapphire radeon rx560
Ram ballistix sport 32 gb
Psu aerocool p7 850W
Monitor LG 22MP68VQ
dvi cable, also tested an hdmi
An m.2 samsung, a crucial ssd and an hdd (probably not important)
Some fans including a corsair watercooler

The zotacs are in the 16 lanes and the sapphire in 8