https://bitcointalksearch.org/topic/list-of-motherboard-that-require-shorting-pin-a1-b17-for-pci-e-1x-to-work-36061
if a card isnt detected with a 1x riser/cable this is the most likely culprit.
Topic: 7950 not liking riser (Read 1494 times)
I just bought 3 7950's and put them in one rig. Two gigabytr and one msi. They are too hot when all placed on the mobo, but when I plug a riser into one of them and loft it, the rig wont detect it. Could this be a power issue? I have only tried using a 1x to 16x riser for this but I didnt think it should matter if I use that compared to 16x to 16x does it?
Which pciex slots on the mobo did you plug the cards into? I've seen boards that had the first pciex1 slot bridged with the top 16x slot, and thus only one or the other worked. Does the gpu's fan spins with the pciex power plugged in? if so, i'd bank on it being the slot. how many 16x/8x slots do you have? how many 1x? 
I still cant understand why people say powered risers.... i have well over 100 gpus, all on risers, none of them powered. 5 and 6 to a rig.
I think you have a bad riser.
There are several people who had their motherboard die or have damage to the ATX connector because they pulled too much power through the board. Powered riser kind of acts like a bypass.
I still cant understand why people say powered risers.... i have well over 100 gpus, all on risers, none of them powered. 5 and 6 to a rig.
I think you have a bad riser.
I think people said increasing the pcie latency in bios can help
Might be time to try a powered riser
I just bought 3 7950's and put them in one rig. Two gigabytr and one msi. They are too hot when all placed on the mobo, but when I plug a riser into one of them and loft it, the rig wont detect it. Could this be a power issue? I have only tried using a 1x to 16x riser for this but I didnt think it should matter if I use that compared to 16x to 16x does it?
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