GTX 280 - Is there a forced shader/core ratio? Can't OC to where I want

[gramboh]

Hi guys,

I'm running a vanilla GTX 280 with 177.83 (power pack drivers from nvidia.com) and EVGA Precision 1.3.2 under Vista x64 Ultimate.

I've been running at SSC speeds (648/1404/1161). Occassionally in Crysis I would notice weird white circles so I started experimenting with my OC in ATI Tool. After 120seconds I get yellow blocking artifacts at SSC speeds. For some reason I suspected it was the shader clock. I backed the shader down to 1370 and can run ATI Tool forever with no issues (648/1370/1161). I wanted to bump up my core and memory while leaving my shader at 1370. For some reason when I can't go over 675 on the core with the shader at 1370. I try 685, 690, 700 etc. and it pushes it back to 675. Note I am running them unlinked.

If I link the GPU/shader I get ~1500 shader at 700 core which obviously will not work.

My question is whether or not there is a minimum ratio between GPU and shader clocks that must be maintained, even in unlinked mode? Also, is there going to be any performance issues trying to push core and memory up with a relatively low shader? I see lots of people around 700/1500/2400, but I simply cannot seem to get my shader over 1400 without artifacts.

Thanks

P.S. strangely enough, my card has just started downclocking to 2D mode. It never worked on any previous drivers (since late July) but has suddenly started in desktop. I wonder if this is related to my OC problem. Might try reinstalling drivers/Precision.

 

[nitromullet]

I had the same type of experience with mine. It does appear that there is some sort of minimum ratio between core/shader.

 

[gramboh]

According to some folks on EVGA's forum the ratio that must be maintained is 2:1 shader to clock. That would explain why I can't keep the shader down at ~1370 while pushing the core to 700+ since it's going under 2:1 (or over depending how you want to phrase it).

Going to do some testing later tonight.

 

[BFG10K]

Yes, there's a ratio lock at the hardware level and has been since the G80. On a 8800 Ultra the most I could drop one was 19% while leaving the other the same.

http://episteme.arstechnica.co...7909965/m/453004231931

 

[gramboh]

It's definitely 2:1 shader to GPU on the GTX 280 that must be maintained or exceeded (e.g. can push shader higher than 2:1 but not lower).

After a bunch of testing I got it stable at 675-1350-2448. 3DMark06 dropped 200 points while Vantage went up about 200 points from my previous settings (648-1404-2322) which was 90% stable in games (I would get artifacts in Crysis after 30+ min and sometimes in DIRT but never in TF2). I'm happy enough.