Adding that second gpu on an older mobo.

[66tbird]

I've been researching this multiple gpu thing for a month with no luck. I'm starting to think my mobo just won't do it. Looking for a little advice before I dig another old rig up and just run two single gpu miners instead of one rig and two cards.

I've got a stable GIGABYTE GA-MA790X-UD4P Mobo (Newegg Item=N82E16813128387), 4GB Ram, dual core 250 AMD something or other CPU and a decent 500W modular gold PSU running Win7-64.

I've got two GPU's, an RX570 and an RX580. I can mine either single just fine and pull 170W or 190W from the wall.  When I add the second card and power up I get no video. The rig just quietly sits there. I've tried different risers, usb link cables, GPU connectors, but nothing changes. I've checked Bios for something PCI-E related and only find a reference to BNG and BNG1 which didn't make a difference when changed.

I'm using the pci-ex16 and the x8 slots. The other slots did the same.

Hopefully it's just something I'm missing in the windows configuration.

Thank you

[CryptoPlay]

Disablçe the crossfire in the registry. There is a clue here in this guide.
Check the Windows part...

http://vega.miningguides.com/p/tuning.html

[66tbird]

Thank you, I just applied that reg tweak and there was no change. Bummer, had high hopes for that because it seemed to make sense.

[66tbird]

Moving things around got it to boot with video and see both cards. It crashed shortly after starting the miner and seemed to make the cards bios unrecognizable. So it's back to re flash and driver basics. fun fun

[lncm]

I bet on the PSU.

I have a second rig with an old Asus Rampage II extreme with a "decent" 500W PSU and after I installed a second video card, the system was unstable and the PSU just burnt....

Problem solved with a Corsair TX650 I has around, no more problems.

[66tbird]

I'll put some attention to the PSU and do a volt drop test under load. Wouldn't surprise me at all since OCZ is no longer in the biz. Just because it's modular doesn't mean it's good I guess. Maybe even worse do to the extra connection's loss.

Thanks

[66tbird]

It was the PSU. The 580 draws 14+amps on boot. That just put that crapily built OCZ into null mode. So I paralleled another crappy psu and it boots. One miner on the cheap.  In the shop it goes below a WilliamsRDM 675-3D Stovetop Firestop. BTW those things have saved me twice, once from a lipo charger fire and another from a 3d printer psu fire.

[burntmytoast]

What are you talking about the 580 draws 14 amps on boot?

[66tbird]

Yes, the 580 was spiking 14A+ on start from what I could catch on my cheap meter. I'm sure it's more but I'm not scoping it.

That psu knocks out at 24A so both cards on that one psu ain't going to mine anything. Crabbed one of those dual psu patch cords and tossed another psu in the mix. It was a relic from 04 rated at 600W rated 17A on the 12V+ rail. It didn't fly either. Dug out an equally old Seasonic 350W with 18A on the 12V rail and it works. yippie!!.. It all worked like it should.

For a day it was rebooting randomly and I have been diligent on the event logs putting out the fires. (thank you google)

 Now I'm into a 24 hour solid run mining a pathetic 40Mhs on a 570 (hymix) and a 580(Micron). I can go a little higher but it gets flaky. I did meet my sub 400W at 370W from the wall though. That's all my grid tie can spare for the year without paying the line fee bs. Bought the cards used, did the thermal paste frankin fan thing, then all the other parts are just old junk computers from my yard sale rebuild/resell days. Hoping to ROI in a couple months. (Aren't we all)

Thanks for the help. It's a great wealth of info within the group.