ASUS P5Q deluxe - cannot get more then 3 GPUs to run

[Takeshi_Kovacs]

One of my scrypt mining rigs has an ASUS P5Q deluxe mobo.

This board has 2 PCI-E X1 and 3 PCI-E x16 slots.

I have a GPU plugged directly into the primary x16 slot and two other cards on risers plugged into the x1 slots.

I'd like to plug in two more cards but, if I plug a riser into either of the other x16 slots, then the card on that riser is not seen and the card on one of the x1 slots is no longer seen. I have tried an assortment of different cards in the slots and this is always the case.

Are there any special tricks that I need in order to get more than three cards running on this mobo?

TIA

[HellDiverUK]

That's a P45 chipset, and only has 16 PCI-E lanes.

See: http://ark.intel.com/products/35133/Intel-82P45-Memory-Controller-Hub

One card is probably taking 8 lanes, the other two 4 lanes each, leaving none free.