I recently got in enough parts to build 2 small 3x 7870 rigs (actually one card is a 7950). I needed at least 1 more power outlet because my first rig (5x 7970) was pulling 1200W on a nearby outlet, but I wanted to get a dedicated one for the first rig also.
26 November 2013
To improve PCIE bus initialization during boot when trying to run x16 GPUs via various PCIE risers, short pin A1 to B17 on ALL PCIE x1 risers (in the unlikely event you are using x4/x8 to x16 risers, look up the proper x4/x8 PRSNT#2 pin and short that one to A1 instead).
I guess I should preface everything below by saying, I'd be happy to hear how PCIE bus initialization really works (in relation to the problem described below) from someone who knows PCIE buses.
Full StoryLast night I had a problem getting multiple Radeon 7970 GPUs running in a single motherboard, 4 cards good --> 5 cards pure chaos, lspci showing 3 cards only, swapping slots, risers, cards all showed that everything was good, just not in any combination over 4 and in fact, some combinations of 4 no good. (Maybe even some with 3).