Two 7850s running drastically differently

[ak49er]

Completely new to this and only in it for kicks so apologies in advanced if this is glaringly obvious to any of you!

I set up an Ubuntu 13.04 box with a HD7850 a couple of weeks ago.  After a bit of initial tweaking I got it running at 315MH/s.  (cgminer3.1.1, Catalyst 13.4, SDK2.6)  It ran like this 24/7 @ 75C / 85% fan speed, overclocked at 1050MHz, memory underclocked at 900MHz.  Rock solid at these settings.

So I decided to add another identical card, (same manufacturer /  part number).  Got it installed and recognized by cgminer without too much trouble, and I'm running it with the exact same config file as the single card - but oh boy, what a difference between the two!  The original card is now running at 78C / 85% / 860MHz, while the new card is running at 73C / 62% /  1050MHz, (i.e. better than the original when it was single).

Now here's some extra information.  At the time I added the card the weather improved and it's considerably warmer.  To get things running as they are now I've pointed a desktop fan directly at the cards in the open case.  I'm guessing that I could expect the original card to run hotter as it's drawing air that's been heated by the back of the new card, (maybe).  I've ordered some PCI-e extender cables so I can get the cards further apart.  Right now I've only got a 500W supply running both cards.  The original card is on the PCI-e connector from the power supply, the new card is drawing its power from an adapter run off two hard drive molex plugs.  (On what I think is two separate supplies from the PSU, but I'm not sure).  The original card is getting 1.138V, but the new one only 1.075V.

So my big question is why is the additional card running so much better than the original, and at a lower voltage?  Both are new, from the same manufacturer and the same part numbers.

TIA for any insights!

[1713498186]

1713498186

[1713498186]

1713498186

[JeanCool]

Hey!

I experienced sth similar. Had one 7950 Gigabyte Windforec 3. After buying second one, the first is significantly lower in temp (alos got extr fan blowing in open case), but the second is running faster! But that differs. Sometimes i stop the cards and start again. Then it changes which one is faster. The values are stable then. I stop and different values again, but stable over time. Somtimes its 1. 650, secon620, then its 1. 630 and 2. 640, then again its both at 650 .... or both at 630 ...canttell why.

So I guess try to restart until you hav good khash/ or MHash/s ... Strange phenomenon and good I'm not the only one experiencing. You as well are not alonge

[ak49er]

Check the ASIC quality with GPU-Z.  Not all cards are made equal.

Anything that runs on Linux?  And what would tell me the quality?  (Can't make it out from the GPU-Z screenshots).

Could they be running different BIOSes?  Clearly they're using the same driver.  How to check in Linux?

[GenTarkin]

agree w/ checking the asic quality, thats a damn nice feature. I bought 2x 7870 tahiti powercolor cards & one card is 75% the other is only 62% .. the one thats less requires higher voltage & runs hotter and consumes more power to reach clocks within 30mhz of the one w/ higher ASIC quality

[ak49er]

If you have a Windows machine with PCIe slot, just put that card in there just to run GPU-Z and read it off (title bar+right click+Read ASIC).

Yeah, I was slow to think of this, but I have that utility on a Windows drive in the same machine.  I just need to reboot in to Windows and take a look.

[JeanCool]

Oh I didn't knew that!

So ASCQuality of 57% and 61% doesnt sound too good, i guess? ... Hm feeling bit disturbed atm to be honest ...

[glendall]

ASIC quality?  Wow that's a really cool feature.  That must be some what new, I used review for a living, and never even heard of such a new-fangled concept. Didn't even know that was possible; I'm gonna go read up on how it comes up with that value. That is really interesting...

[ak49er]

Well I never did get around to checking things out using GPU-Z, but today more weirdness.  Halfway through the day I noticed that the hot GPU had dropped down to about 70C.  I had been running that one at 900MHz while the other was still running at 1050MHz.  So I decide to raise it back to 1050MHz to see what would happen.  Sure enough the temperature went up to 77C and the fan pegged out at 85% - for about a minute, then it started dropping!  Now both GPUs are running at under 75C and below 70% fan speed.  Both at 1050MHz.  Both hashing at the same rate.  And it's been this way for the past few hours.  Beats me what's going on.  This is even better than when I had it running as a single.