It depends on the brand of power supply and efficiency as well as the rest of the components in the rig.  I've run two 5770s off an Antec Earthwatts 80 plus certified 430w.

4x 6870s runs just fine... they are the replacement of the 5830.

what did you end up going with, I'm thinking of an additional rig with 4 5770s.

In windows, you need to plug in a monitor or a dummy plug for guiminter to see your cards properly.

Hi Kiv,

Any ideas on this issue I'm having:

http://forum.bitcoin.org/index.php?topic=3878.msg192377#msg192377

I'm runing windows 7 ultimate 64 bit ... clean install with all updates, updated java, and latest version of guiminer.

I've seen others having this problem as well:
http://forum.bitcoin.org/index.php?topic=3878.msg145258#msg145258

Thanks!

any updates on this.  I have the same problem and I posted a bug report here:

http://forum.bitcoin.org/index.php?topic=3878.msg192377#msg192377

One additional piece of info.  If I boot up with all four cards plugged in, but with the fourth card not hooked up to a monitor, guiminer will open and I can mine with the 3 active cards.

Switching cards/slots/power cables/etc has no affect.

Hi,

I hope someone can help me with a problem I've been having with guiminer on a 890fxa-gd70.

I can run 3 6870s no problem.  But when I install a 4th 6870, guiminer crashes when I start it with this error:

Problem signature:
  Problem Event Name:   APPCRASH
  Application Name:   guiminer.exe
  Application Version:   0.0.0.0
  Application Timestamp:   4918019c
  Fault Module Name:   StackHash_0a9e
  Fault Module Version:   0.0.0.0
  Fault Module Timestamp:   00000000
  Exception Code:   c0000005
  Exception Offset:   72747369
  OS Version:   6.1.7600.2.0.0.256.1
  Locale ID:   1033
  Additional Information 1:   0a9e
  Additional Information 2:   0a9e372d3b4ad19135b953a78882e789
  Additional Information 3:   0a9e
  Additional Information 4:   0a9e372d3b4ad19135b953a78882e789


If I shut down, then pull the card out, and boot again, guiminer runs with no problem.

I've tried deleting the saved guiminer settings, and running a clean install.

I'm running 11.5 ati drivers with 2.4 sdk.  I ran the ati driver install with all the cards plugged into monitors.  All four card show up in windows including gpu-z.  GPU-z shows that OpenCL is available on all 4 cards.

Any help is greatly appreciated.  Thanks!