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Author Topic: Strange 3 x 5850 Problem on nForce 780i Mobo  (Read 1636 times)
Meatball
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May 27, 2011, 12:06:46 AM
 #1

Hey guys,

I'm running a machine with 3 5850's and have noticed a weird problem.  Whenever one of the cards is mining, the other two drop down into the khash/sec range, yet as soon as I stop that one from mining, the other two jump right back up to full speed.



The cards are running on an evga 780i nForce SLI with 2 GB Ram, a Celeron 430 CPU on Win XP.  Have Catalyst 10.11 & Stream 2.1 installed.  PSU is a Corsair HX850 and even with all of them chugging it rarely goes over 550 watts.

I'm not overclocking at all and not really sure what's going on.  Any thoughts?

Update:  Updating to 11.5 Catalyst & 2.4 Stream doesn't seem to help.  Cards 2/3 are still getting bad speeds and using afterburner I see those 2 GPU's core and memory clocks dipping down from 725/1000 to 157/300 every few seconds.
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Meatball
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May 27, 2011, 02:37:49 AM
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Not sure what the deal is, but I've pulled every card, tried every order of slots, but no matter what I do I can't get all three cranking at the same time.  I'm going to guess it's a chipset problem considering I'm trying to make 3 AMD cards work on an NVidia chipset.

Anyone know of a decent 3 - 4 GPU board that will handle AMD cards?  If it's LGA 775, all the better, then I won't have to buy a new CPU.

Thanks!
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May 27, 2011, 02:50:40 AM
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Crossfire enabled/disabled?

I have had 4 x 5850 on an Asrock P43DE. You have to use x1 extenders though of course. See Cablesaurus for them.
Meatball
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May 27, 2011, 12:50:22 PM
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Hmm, found another little wrinkle.  I tried a few other miners.  Diablominer does the same as GUIMiner and kills the performance of two of the cards unless the third is disabled.  For some reason phoenix seems to be able to allow all 3 to run, albeit a bit slower than normal.  They're running around 225 MH/s each.
mewantsbitcoins
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May 27, 2011, 01:03:24 PM
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try different switches

also lower your memory clock and raise your core clock
5850s should be doing over 350Mh/s

https://en.bitcoin.it/wiki/Mining_hardware_comparison
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May 27, 2011, 01:12:54 PM
 #6

Hey guys,

I'm running a machine with 3 5850's and have noticed a weird problem.  Whenever one of the cards is mining, the other two drop down into the khash/sec range, yet as soon as I stop that one from mining, the other two jump right back up to full speed.



The cards are running on an evga 780i nForce SLI with 2 GB Ram, a Celeron 430 CPU on Win XP.  Have Catalyst 10.11 & Stream 2.1 installed.  PSU is a Corsair HX850 and even with all of them chugging it rarely goes over 550 watts.

I'm not overclocking at all and not really sure what's going on.  Any thoughts?

Update:  Updating to 11.5 Catalyst & 2.4 Stream doesn't seem to help.  Cards 2/3 are still getting bad speeds and using afterburner I see those 2 GPU's core and memory clocks dipping down from 725/1000 to 157/300 every few seconds.

What is your cpu usage at when starting 2 cards compared to 3 cards ?

It shouldnt ever use that much cpu but in rare cases people report huge cpu usage when mining on gpu's

...In the land of the stale, the man with one share is king... >> Clipse

We pay miners at 130% PPS | Signup here : Bonus PPS Pool (Please read OP to understand the current process)
Meatball
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May 27, 2011, 01:26:41 PM
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Hmm, you may be on to something.

Running all 3 in Phoenix takes up about 10-15% CPU, all 3 in GUIMiner takes up about 50-55%, I noticed as soon as I stopped that first card in Phoenix, CPU usage for the other two dropped down to like 2-4% combined.  In GUIMiner, stopping the first one dropped the CPU down to about 4-5% for the other two combined...

Meatball
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May 30, 2011, 06:00:07 PM
 #8

I'm not sure what finally fixed this, but I ended up moving to Windows 7 Pro and haven't had a problem since.  Maybe a problem with XP, but the 780i can recognize/use all 3 AMD cards without a problem.

Thanks to everyone that offered suggestions.
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