Bitcoin Forum

I am trying to use 2 AMD cards at the same time and I'm having some hiccups, so i'd be grateful for any help.

On my PC, Abit P5Q pro motherboard, I have a 5870 that I want to use for mining all the time and a 4870 that I want to use for the desktop and games. The 5870 device 0 in the top PCIe slot and the 4870 is device 1 in the lower PCIe slot. At the moment, the only way I can make it do what I want is as follows:

Crossfire the 2 cards.
Boot up with monitor attached to 5870
Use MSI Afterburner, set 5870 as master and adjust settings for mining
Run miner
Disconnect monitor from 5870 and reconnect to 4870
Run games

If I boot up connected to the 4870 or swap the monitor over to the 4870, MSI Afterburner won't let me change any settings on the 5870, even if 5870 is set as the master card. If I now change the master card in Afterburner to the 4870, I can adjust this cards settings.

Is there a simpler way I can tell the PC to mine with the 5870 and play games with the 4870? I thought I wouldn't need to Crossfire, but if I don't, the card that isn't connected to the monitor do anything.

/edit Should have said that I'm running Windows 7, 64 bit, and AMD 11.3 Catalyst.

Hi,
You should use a dummy plug for the card whose don't have the monitor plugged. You don't have to have crossfire and I recomend to set the 4870 in the primary PCIe slot which you will use as primary.

The dummy plug simulate that there is a monitor plugged and you can use the 2nd card.

Here you have a link to make a dummy plug. You only need a DVI-VGA adaptor(which comes with every card) and some resistors.

http://www.geeks3d.com/20091230/vga-hack-how-to-make-a-vga-dummy-plug/

I hope it will help you. I have a 5850 in the primary slot and a 5770 with the dummy plug mining and it works for me perfect.

Thanks for the reply, I'll give it a go.

+1 here, works like a champ.

Also potential aftermarket mod option here if someone wants to start selling these, not everyone has easy access to resistors to actually make one, and based on the # of forum posts a ton of people are doing the "monitor swap" trick.

Are you guys kidding? I thought the dummy plugs era has long gone.
I remember having to use those for multiple nVidia 8 and 9 series cards, but later, it was solved with a new driver update.
Since then, I threw away all of my dummy plugs.

Where can I buy resisters locally? Would Radio Shack have them?
Do I need to solder it into the DVI to VGA adapter? Or can I simply insert it into the pins?

I see that there is a ohm rating and a W rating on resistors.
I know to get anything from 50-150 ohm, but what about the W rating?

I'm currently using 1/2 W 68Ohm resistors, they fit perfectly into the plug and have yet to short out and destroy my rigs.

yes, i ended up getting 1/2W 100 ohm