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Cant get 2x Asus 4870 to work in Crossfire on ASUS P5KC.

Last response: in Motherboards
January 11, 2010 4:43:45 PM

Hello, this is my first post here! Hope to find some help.

I have just bought 2x Asus 4870 512mb. I have installed everything as power cables, bridges, etc..

The computer:
2x 4870 512 mb
Asus P5KC
2x 2GB DDR2
intel 2180 cpu
Antec 700w PSU

I began to reformat the computer. Started with the latest Windows 7 64bit. Installed latest Intel drivers, Catalyst 9.12 for win 7 x64 etc.. Installed everything and thought that they would work, but not.

In the catalyst control panel, I can not even activate the crossfire option. In the "graphics hardware" option in the CCC it says "Primary Adapter" and "disabled adapter".

Things I have done:
Updated motherboard bios to latest
Clear CMOS, run with bios defaults
installed win7 installed both 64bit / 32 bit
installed vista 64 bit
reinstalled drivers 2-3 times
tested 9.10 and older drivers
tested with 1 or 2 crossfire bridges
tested each card one at a time, both work well on both single pci-e ports.
cooling is good, with a few extra fans

I've also thought about what I should change the BIOS, there are not many settings that I can relate to Crossfire, I can not, for example manually change the speed of PCIe ports (8x etc). There is a setting called "PEG / PCI" and "PEG plug and play" these i have changed but whithout any results. I there another option in BIOS i should change? Please help me.

here are some print screens from my system

a b V Motherboard
January 12, 2010 4:13:37 AM

My only suggestion is to check if you've properly connected both cards to your power supply.
January 12, 2010 8:57:56 AM

r_manic said:
My only suggestion is to check if you've properly connected both cards to your power supply.

Hi, yes both cards are properly connected and they work just fine when i connect a dvi cable to each of them. may the problem be my motherboard? it has support for Crossfire, but not CrossfireX?
Related resources
January 12, 2010 10:49:20 AM

i used to have the same problem with my 2 4850's. My problem was that there was not enough power on the rails i was using.. I switched the pci-e power connectors to a different rail and it worked great..

try changing the way you are connecting the power cables (if your antec has more than 1 rail)

also, newegg says the blue slot is at x16 and the black slot is at x4 or x1.. not sure what that means.. might not be enough bandwidth for 4870's..
January 12, 2010 1:24:42 PM

I will try with a new OCZ 700W tomorrow or so, but its weird because they seem to work just fine. thx for the idea!