Rig ok with 2 GPU but problems with adding 3rd.

[sphornby]

Hi guys, Im in the process of setting up my rig and getting more cards as I go

I started with 2 and have just bought another 3, all to run through one motherboard. However, I am having trouble with just adding in the 3rd at the moment.

I can crunch away all night long with 2 graphics cards, but as soon as cgm boots with the 3rd card in, the system shuts off instantly. Doesnt even restart like I told the bios to.

My rig specs:
AsRock FM2A85X Extreme6 mobo (has 3 PCIEX 16 slots, however I can see that one is 8x and the 3rd one is 4x)
A4-4000 APU
8GB Corsair ram
Crucial AX1200i PSU
Gigabyte R9 280X (x3) - modded bios to run at 1150mv as opposed to the default 1200. I have tried default and the same thing happens. 2 cards run fine with 1150.
Xubuntu 13.04 / cgm 3.7.2

Ive built an aluminium open air case and the GPU's never go above 80C - Ive even run a wire from the top bar (where the graphics cards screw in) to the bottom, ensuring good grounding. Ive got dummy plugs in all cards. Im using powered PCIE 16-16x riser cables plugged in to different molex connectors off the PSU. Got a couple 1 - 16x risers coming soon hopefully so cant try the 1x slots yet.

Thats about all I can think of that would be of any use to anyone who is kind enough to lend assistance but if you need more, then please ask!

Any ideas guys?

Thanks

[sphornby]

Bit of an addendum,

Just tried the rig with 2 of the cards with powered risers and it does exactly the same thing. Maybe a problem with risers? Ive got 6 of the damn things and the same thing happens. Cant be all of them, surely?

Maybe the motherboard doesnt like them??

Any help greatly appreciated before I go ahead and order a different mobo.

[philipma1957]

okay try  1 card in first slot .  then try the same card with a powered riser in the first slot.
 
 lets say that works.  try the same card in the second slot.  the try the card second slot same good powered riser.


sucks as it takes a while to do this.   move to the third slot.  pretend all good.


  this mean
 A all slots work
B the riser works
C that one card works.

use the second card all alone  repeat all tests.

 pretending that works use third card.

you now know all cards are good.  all slots are good and the one riser is good.

 test again with second riser.  pretend all good.  this means 2 good card 3 good slots 2 good risers.

do the same tests using 2 cards 2 slots and 2 risers.

 if it fails then there is a mobo or a software issue.

  I would try to be encouraging  as tweak and test of gpus can take 2 or 3 days.

edit what other miner software can you use?

BTW  I hated risers tons of problems with them.

[_Crash_]

Seems to be a power issue. I tried my Radeon HD 4series inside my homeserver with a 250W supply, boots up and shuts down. It does this 10-15 times before finally booting up. I'd try a higher Wattage power supply.

[dermo]

weird, R9 280X 200w each

[sphornby]

Yup, turns out it was my PSU. Got a different one in and no problems.

Thanks guys.

Also the R280X draws 250W when mining. http://media.bestofmicro.com/3/G/404476/original/05-Power-Consumtion-Torture.png

[dermo]

Yup, turns out it was my PSU. Got a different one in and no problems.

Thanks guys.

Also the R280X draws 250W when mining. http://media.bestofmicro.com/3/G/404476/original/05-Power-Consumtion-Torture.png

thanks for infos