280X crossfire problem, mobo or PSU?

[mid_gen]

Just bought a couple of XFX 280X to upgrade the 6950 (yes, it's going to be doing some mining), but having problems with the second card in.

System is :

Asus P8Z68-V LE
i5 2500
16GB
Couple of SSDs etc
Corsair AX850

With the second R280X in, the system locks up within a few seconds of the driver loading.

I didn't skimp on the PSU, but the motherboard was the cheaper part, it only supports 16x/4x. Is the problem the R280X needs a 16x slot? I thought a good quality PSU like the AX850 could handle two cards ok...

ta

 

[mid_gen]

Update...

Tried each 280X individually, ran some BF4, cgminer, both running perfectly individually.

Moved single 280X to the black PCI 4x slot....system won't even boot.

Put 280x back on the 16x slot, put 6950 in 4x slot, system freezes after a few minutes, ATI drivers have a spazz first.

Can someone tell me if a Corsair AX850 should definitely be able to run 2x 280x before I go ***** a wad on a new mobo/cpu

 

[shankly1985]

Random guess does the Motherboard support Crossfire?? If it was indeed a Cheap board they is a chance it dont support this.

Edit
Just looked and it sure does support this.

Edit2
That PSU is more than enough

 

[shankly1985]

A 6950 and 280 will not work with each other for a start.

Try doing a fresh driver install. Download DDU from here
http://forums.guru3d.com/showthread.php?t=379505

Boot PC into Safe mode and run the Recommended setting, PC will Auto restart.
Install latest AMD driver 13.12
64bit
http://support.amd.com/en-us/download/desktop?os=Windows+7+-+64

See how you get on tomorrow

Bed Time
Good luck.

 

[mid_gen]

Will give the drive cleanse a go tomorrow.

Haven't even got as far as enabling crossfire, just having two GPUs (either 2x 280x or 1x6950 + 1x280x) installed and powered at once is enough to lock up the system.

I should be able to run a single card on the black second PCI 4x standalone though shouldn't I? Beginning to suspect that slot is faulty.

 

[mid_gen]

One more question, will a 280x saturate a PCIE 2.0 4x lane anyway? If so I might as well update to a mobo with a better PCIE spec.

Will check the mobo bios updates....

 

[shankly1985]

Are you connecting the PCI bridge connector?

 

[mid_gen]

Sorted, thanks

Updated BIOS (it was on a 2011 version)
Disabled the HD4000 graphics use with add-on in BIOS (I was using it to drive a cheapo D-SUB monitor).
Safe mode cleanup of drivers
Install 13.12 drivers.

Working a charm....well, it's doing just over 1.4MH/s. Need to improve my cooling, so off for a couple fans and a DVI-D-SUB converter and I'm golden.