Due to heat problems, I've been looking to get some risers - and they finally arrived. I got 100 cm flexible USB cable risers, with SATA power. They look impressive 3 filter caps and a VRM on the riser board.
Anyway, the first thing I found was that no cards would be detected on the risers until I set the mobo BIOS to PCI-e v1.0.
So far, so good. So, one at a time, I transferred cards from mobo onto riser cables, and after a few false starts, I had 2 cards running on risers, and 1 on the mobo.
That's when I start to get adventurous, and connect a 4th card to a 1x PCI-e slot, and power it via a 2nd PSU. All the connections are double checked. The riser is in the slot the correct way round, etc.
Link the PSUs with a dual PSU adaptor, and power up.
*Sizzle* *Pop* *Crackle*
I recheck all the connections, and they are definitely correct.
Thinking I made a mistake, I decide to have another go.
This time, I connect directly a 1x PCI-e slot with a 4th card, after triple checking everything.
*Sizzle* *Crackle* Sparks. Another motherboard now dead.
I don't get it. I've built dozens of PCs in the past, and built a heap of mining rigs, albeit without risers. I've done dual PSU before.
What could have happened? What was cause sparks and sizzling and burn out a mobo. I've looked at the PCI-e riser design, and the power pins are not connected on the riser, so I don't see how a power surge or something could have come from the 2nd PSU back feeding the PCI-e slot.
Any ideas? Could it be a bad riser card? I've run a multimeter over it, and there don't appear to be any shorts or anything. I'm completely baffled.
Where did you get the risers? Do you have an image of the burnt 1x PCI-E slot? If not, where did the crackle/spark happen?