I have a rig with 3 x R9 280x's ,a MSI 990fxa mobo,600 watt PSU and 750 watt PSU.

The 600 watt runs the Mobo, CPU and a single R9 280x.
The 750 watt runs the other 2 x R9 280x's.
The Rig boots up into BAMT and all the cards are picked up but when it starts mining the 2nd PSU and the 2 x R9 280x's cut out!
The rig works fine with a single R9 280x's on the 750 watt PSU.

Thanks for your help !

!Bullet!