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7900gt sli overclock help needed

Last response: in Overclocking
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November 26, 2006 7:24:49 AM

I have the cards set in SLI mode. When I run 3d programs (3d mark or games) the second video cards temp change from 42 idle to 48 load. The First video card however changes from 43 idle to 68 load. If I swap the cards over it is the same. So my main question is are both video cards being overclocked or just the first one? I am using coolbits to overclock and am getting 13350ish in 3dmark 05.

All temps are degrees celcius
Both cards use VF900 coolers, and 93.71 drivers
Overclock is 650core 850 mem (volt mod).

Cheers, Michael.
November 26, 2006 7:59:32 AM

are you using after market coolers? if so , check to see if the second card's cooler is installed right. Once i didnt put a cooler on tight enough and i was get above normal temps :oops: 
November 26, 2006 8:30:23 AM

Im using vf900s on both cards. I swapped the cards around, the card in the second pci x slot is always the cold one so its not a cooling problem,.
It just doesnt seem to be overclocked as much or working as hard as the primary card.

Cheers, Michael
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November 26, 2006 9:09:52 AM

yeahh cause the primary one is.. primary. i guess that means that that is meant to be used more excessively ..right? try them seperately and yeah...

maybe its the airflow not getting to the 1st card..
November 26, 2006 9:15:04 AM

maybe u could run them at stock and see what happens
November 26, 2006 9:39:12 AM

I think you are right about the Primary card doing more work, seems to be the logical answer. Seperately both cards score 10400 in 3d mark 05 and both full load hit about 60 degrees celcius. Also both cards were tested for artifacts using ati tools and worked fine. The second cards fan is very close to the X-FI sound card so it should be hotter if airflow is the problem.
November 26, 2006 9:40:49 AM

At stock speeds the temps are lower, however the temp difference between the two cards remains quite substantial.
November 26, 2006 10:57:46 PM

try to run each in single and compare the temps
November 27, 2006 10:12:32 AM

are both cards the same ie
is one an Asus 7900GT and the other a Gigabyte 7900GT????

I have similar problems with my SLI setup because the cards were made by differnt ppl...
November 28, 2006 3:01:34 AM

it really shouldnt matter casuse both will be using the 7900gt chipset ( its the g71 right?)

if both cards run hotter in primary the the conclusion is that the primary slot card will always be used more.
November 28, 2006 3:22:14 AM

The evga 7900GT has a differnt HSF (the HSF covers the whole PCB)

The XFX 7900GT has a volt mod + its slighly oced

Gigabyte and Asus use differnt types of memory

All the cards above use a G71

But they are differnt and run at differnt temps!!!

The primary PCIe is always closer to a hot NB.... (north bridge on SLI MBs are alwayz kinda hot)

However if one PCIe lane was actually faster or hotter than the other, how would SLI work properly? considering it SLI shares the work load between two GPUs by exactly half???
November 28, 2006 1:12:58 PM

The evga 7900GT has a differnt HSF (the HSF covers the whole PCB)

The XFX 7900GT has a volt mod + its slighly oced

Gigabyte and Asus use differnt types of memory

All the cards above use a G71

But they are differnt and run at differnt temps!!!

The primary PCIe is always closer to a hot NB.... (north bridge on SLI MBs are alwayz kinda hot)

However if one PCIe lane was actually faster or hotter than the other, how would SLI work properly? considering it SLI shares the work load between two GPUs by exactly half???
November 28, 2006 2:39:13 PM

The most likely answer is that the 1st card would not be getting as much airflow, as the 2nd (bottom) one to cool it. I have a friend with the same thing and those zalmans are big, the fan nearly reaches to the bottom card... right? Much of the cooling potential of the zalman is due to the numerous copper fins, but "straight down" or in this case "straight up" cooling onto a chip is not the most efficient way of cooling, it creates a deadspot right over the chip, not as good as... say... side cooling. That being said, the zalman is a fine, quiet, very good cooler, better than just about any stock cooler, it just would be even better (though probably louder) if it was a side cooler. It's why I also prefer the side cooling cpu fans, like zalmans and the arctic cooler freezer 64 (which I own). Though, if space is a concern they are much much taller.
This is probably the biggest reason, because, also you are drawing hot air from the other side of the card below (the "top" of these cards can get damn hot thru the pcb) and are drawing it right onto your other gpu.
Also, the probablility that one card is doing more work than the other is quite high, for example if you forgot to enable SLI mode through the driver itself and not just the motherboard.
Also, not every game uses SLI in the same as the next, meaning they don't always, if at all, spread the love between the two cards.
You can figure this out, by just removing the 2nd card, or disabling the SLI in software thru the nVidia driver again, and see the performance difference.
Finally, long ramble short, assuming that you are getting a good performance increase with SLI (i.e. you've been able to prove it's actually working) your temp in the "hotter" card is well within spec and I wouldn't worry about it.
a b K Overclocking
a c 272 U Graphics card
December 2, 2006 3:33:22 PM

Your mobo may be the culprit, I use two different cards an Asus and an XFX OC both of them run to within a degree or two of each other whether the Coolbit hack is used or not however my mobo is an Abit A8N32X and runs both Pci-e slots at 16x yours does not, it runs the Pci-e slots at 8x + 8x when in Sli mode.
!