A tale of two 7900GTs

[vois2]

Thanks in advance for reading. If you have the patience to read this, you'll probably laugh at how thorough and plodding my planning/testing has been, only to see it all go down the tubes. In the end, I now seek advice: Is it my power supply?

I recently bought two (2) XFX 7900 GTs, one of which I purchased as a gift for a friend. While I had both cards in my possession for a while, I benchmarked them relentlessly, each card getting several benchmarking days in the same box. The two cards performed exactly the same in every manner, including temperature ranges in each card. My conclusion is that these two cards are thus identical in performance.

These XFX 7900s at stock are 470/1370 . Before any of the below, I extensively tested my 350W PSU for constant and consistent voltage on the +12V and +5 rails. Also, the machine has never had any power-related problems before.

So I shipped off one card to my friend as a gift. He immediately used Coolbits on his card to o/c to 562/1612 . He didn't crawl up the clocks, either. He just went straight to 562/1612 using Coolbits recommendation. Zoom. All of his benchmarks increased 15-20% thanks to this sweet overclock.

I am decidely more cautious, so I inched mine up only a tiny bit to 474/688 ... an almost microscopic overclock. All was well after some days, so based on his experience I decided I would FIRST install a Zalman VF 900 Cu VGA cooler, and THEN follow in his footsteps on a path to a high overclock.

Well, the Zalman certainly does a great job of cooling. All my temp ranges slid colder by 16-20 degrees Celcius. Sweet! So now I was going to have a much cooler card while I started to overclock. This joy was my last moment of success -- it's all been a wash since then.

I used Coolbits to take it to 559/1600 (almost identical to my friend's o/c). Ran 3dMark05 and enjoyed about a 5% increase in performance. Hmm, well, not nearly the gain of my friend, but better performance nonetheless. Then the fun began...

I wound up 3dMark05 for another go ... result: Crash, BSOD, nv4_disp infinite looping. I recovered and reapplied drivers (I use DriverCleaner properly always) ... now for another 3dMark05 test. Result: Fizzle pop random pixelation all over the place, freezing. I cleaned with DC again, now using RivaTuner, and lowered the clock substantially to 500/730 ... result: black screen, monitor gets no signal. Keep in mind that I continue to use DC Pro so that I can start fresh as I switch between Coolbits and Rivatuner ... and by now I have worked my way downward on the clocks ... at this point today it won't even overclock to the microscopic 474/688 I had with the stock cooler a few days ago. "Test settings" for anything above 470/685 and sometimes, pixelation, sometimes black screen, but always Windows crashes.

So basically I am back to a cooler running card, but it is at stock timings, so that the Zalman cooler ends up being a useless expenditure.

Here are my questions:

(1) I did get a full run of 3dMark05 on my FIRST go at 559/1600. Why would it run once and give me a 3dMark score, and then refuse to run 3dMark05 again at any overclock?

(2) The Zalman cooler fan requires power directly from the PSU, and this has to be pulling more power than the stock fan did because the stock fan needed power only from the VGA board itself. Do you think this higher power draw with the new Zalman fan could point the way to a need for a new PSU based on the errors described above?

(3) I have the Zalman fan running directly from a 4-pin molex to 3-pin converter, so she's getting juice straight from the PSU. I have several other molex connector available in there, and I have read about load balancing and what not, but I don't understand it. Is there any point to my trying a different molex connector on a different line bundle?

Thanks again. All thoughts much appreciated.

 

[Modular]

You could try swapping out your friend's PSU and see if that makes any difference, but you have to understand that every system, even those which are composed of identical parts, will put up different numbers and overclocks.

Does the card artifact at stock settings? It sounds like it doesn't, so that might suggest that it is PSU related. I would try the friends PSU and check back in here.

 

[Vinnybcfc]

As Modular has said; exactly the same pieces of hardware can have varying results

The fan wont use much power I cant imagine it making the difference, I would look at the PSU

If you want to run the Zalman off a different supply disconnect one of the exhaust fan headers and hook it into that, I dont think it will be of much help but if you really want to try it hooked into something else

 

[TheRyuu]

*points and laughs*

<------*thinks about himself*

*then cries*

Yea, that kinda reminds me of mine (back in the day). I'm not sure what happend but it stopped and then hardly ever crash anymore.

 

[vois2]

Thanks to everyone for the replies. I've ordered an OCZ 520W Powerstream PSU and I'll put it in soon. I don't know that it will definitely cure the issue of being unable (now) to overclock, but it will be an interesting test to try and isolate if the PSU is the problem. This will give me 33A on a single rail, as opposed to 18a and 18a on dual rails, which is the situation of my current PSU. (I don't know what the diff. is effectively between single and dual rail, I am just giving you some numbers.)

Someone reminded me that overclocking with a PSU at or near the minimum recommended specs that a VGA card requires, is not a good idea. So with my 350W PSU I guess I am right at the minimum now. We'll see if the 520W helps out on any of the issues.

 

[nullpointerus]

Originally posted by: vois2

(1) I did get a full run of 3dMark05 on my FIRST go at 559/1600. Why would it run once and give me a 3dMark score, and then refuse to run 3dMark05 again at any overclock?

Video cards have additional components onboard to support and supply voltage to the GPU and RAM chips. I have read in overclocking guides that these supporting components can get extremely hot, especially on the early versions. It's possible that they become slightly damaged from the heat and refuse to run that high again. One of the 7900GT volt-modding guides had a mini-guide to cleaning the back of the card where these components lie - give that a shot.

 

[JBT]

maybe your just doesn't OC as high? That could easily be the problem...

 

[TheRyuu]

Time for a vmod (if you didn't do it yet)?

 

[vois2]

nullpoint wrote: "these supporting components can get extremely hot, especially on the early versions. It's possible that they become slightly damaged from the heat and refuse to run that high again"

That's an interesting comment. After I install the 520W PSU early next week, I should be able to know more. If the new PSU gets in there and I am still unable to overclock, then I'll start to investigate this as a possibility. You mentioned this was a problem with early cards and I don't know if you meant early stock of the 7900GTs from this calendar year, or earlier GPU generations.

 

[vois2]

JBT wrote: "maybe your just doesn't OC as high? That could easily be the problem..."

I've since learned that all one can do is keep their fingers crossed for overclocking, since results vary so widely from component to component. However in my case, the fact that I cannot now overclock at all (not even +1.0 MHz!!) is odd due to the following:
* I had it OCd with stock cooler to 474/688 (very slight o/c) for quite some time
* I had it OCd to 559/800 with the Zalman cooler for one successful run of 3dMark05

Now, it won't support any overclock at all. So while it's certainly true that my friend's card may simply o/c better than mine, I should be able to do at least *some* overclocking on my card at this time. Right now, I am thinking that I have too little headroom in my PSU *plus* the idea mentioned above regarding the refusal of components too heat up after slight damage.

 

[vois2]

TO nullpointerus:

Thanks again for the hint about cleaning components on the underside of the GPU card. I found those threads and spent a good hour cleaning with isopropyl alcohol. (Please note I did not do a volt mod on this card. I merely followed the cleaning instructions for it.) Now it will be early next week when I next try to overclock (slightly) this card, for I will do so only after putting in a new 520W OCZ PSU. Since I'll next try o/c with both the PSU and after your suggested cleaning, I'll never know precisely if the cleaning helped, but it can't hurt. Thanks for your input.

 

[TanisHalfElven]

Originally posted by: vois2
nullpoint wrote: "these supporting components can get extremely hot, especially on the early versions. It's possible that they become slightly damaged from the heat and refuse to run that high again"

That's an interesting comment. After I install the 520W PSU early next week, I should be able to know more. If the new PSU gets in there and I am still unable to overclock, then I'll start to investigate this as a possibility. You mentioned this was a problem with early cards and I don't know if you meant early stock of the 7900GTs from this calendar year, or earlier GPU generations.

get a nice infrared thermometer and run the card to atock and see the temps. shouldgive you an idea.

by stock i mean nvidia stcok speed/.

 

[vois2]

TO tanishalf:
Actually, I left out all the details of my temperature benchmarking over time, but here they are. Temps have never really been a problem.

At 470/685 (stock timings stock cooler):
dead cold: 48 C
idle in Windows for 15 min, 2d : 51 C
maximum stress from anything I could throw at it: 64 C


At 474/688 (stock fan)
dead cold: 50 C
idle in Windows : 53 C
max stress: 67 C


At 470/685 with Zalman cooler:
dead cold: 29 C
idle Windows: 36 C
max stress: 47 C

 

[vois2]

This is the original poster just following up on the resolution of the original problem. That problem was the discovery that I could not o/c my 7900GT by even one megahertz. I suspected the PSU was the problem. Thanks especially to Modular, Vinnybcfc, and nullpointerus for helping me. I replaced the Dell 350W PSU with a 520W OCZ Powerstream power supply, and the problem went away. I now have the card o/c'd to 562/810 (from 450/685) and this provides about a 5% improvement in benchmarks and game fps averages. Ironically, even at this overclocked state, temps went down by 3 degrees in all ranges of idle and stress. I guess this has to do with the card fan receiving more stable power? The only disadvantage to the 520W OCZ is that it makes my CPU fan spin at astronomically faster rates when the CPU is very stressed. This isn't too often though -- the worst is during the CPU tests of 3dMark.

 

[gamefreakgcb]

Originally posted by: vois2
This is the original poster just following up on the resolution of the original problem. That problem was the discovery that I could not o/c my 7900GT by even one megahertz. I suspected the PSU was the problem. Thanks especially to Modular, Vinnybcfc, and nullpointerus for helping me. I replaced the Dell 350W PSU with a 520W OCZ Powerstream power supply, and the problem went away. I now have the card o/c'd to 562/810 (from 450/685) and this provides about a 5% improvement in benchmarks and game fps averages. Ironically, even at this overclocked state, temps went down by 3 degrees in all ranges of idle and stress. I guess this has to do with the card fan receiving more stable power? The only disadvantage to the 520W OCZ is that it makes my CPU fan spin at astronomically faster rates when the CPU is very stressed. This isn't too often though -- the worst is during the CPU tests of 3dMark.

Dude, you used a Dell PSU to run a 7900GT and then tried an overclock? :shocked:. I am shocked your computer didn't go down in flames.

 

[vois2]

gamefreakgcb wrote: "Dude, you used a Dell PSU to run a 7900GT and then tried an overclock? . I am shocked your computer didn't go down in flames. "

Actually the Dell 350W PSU has no problems running the 7900GT at its stock of 470/1370. There are a lot of folks at the Dell forums using the 350W PSU to power their 7900GTs -- I've kept an eye on that since the G71 series came out with the 7800 line. However, it sure didn't have enough overhead in that PSU to try an overclock. I didn't consider that, at first. The OCZ 520W provided the overhead needed to o/c, though. Someone remarked that overclocking with a PSU that provides at or just above the recommended wattage is not recommended. That makes perfect sense to me now.