GPU, PSU, or MOBO issue?

[JDB4LFE]

I have 2x Sapphire Radeon 6950 OC (Dirt 3 Edition) video cards, an MSI 890GXM-G65 motherboard, and a Thermaltake TR2 RX 850w PSU. Ok so with that stated, I'm having an issue overclocking my video cards. With a single card (either one) in my system, I can OC the gpu to about 890-900 on the core clock and 1300 on the memory (using sapphire trixx and msi AB) and staying stable 24/7 with stressing through 3D Mark Vantage. With both cards in I can't get past 840 core clock with stock memory settings (or OC'd) without a system crash running 3D Mark Vantage. I know it's the gpu's crashing because my screen goes to a grey'ish color with lines on it, but my system stays running (sound and all still works just no video). It's not a temperature problem, I have adequate cooling in my case. My gpu's never go over 80c (thats the top one bottom never goes over 70c). I'm curious as to if it's a PSU limitation with the power draw from the cards or if it might be a motherboard problem not allowing me to utilize the 2nd pci-e slot at its full 8x speed. Any ideas? suggestions?

[AMD_Nemesis]

Multicards usually cant achive as high as 1 card sorta the same with cpus you enable only 1 core to get the highest oc, So sorry there is nothing you really can do about that but it shouldnt really matter since you have 2 6950s.

[Liam-McShane]

Multicards usually cant achive as high as 1 card sorta the same with cpus you enable only 1 core to get the highest oc, So sorry there is nothing you really can do about that but it shouldnt really matter since you have 2 6950s.

I disagree with this. When i was running 2 7870's i could achieve identical clocks as a single card, although i could be an anomaly.

 

JDB4LFE have you tried testing one card in the number 1 PCI-E 16X slot with the overclock, then trying the same card and the same overclock in the second PCI-E 16X slot? 

[JDB4LFE]

actually no i haven't Liam. thats a good idea, i'll try that. on the note of not being able to OC multiple cards, i know for a fact its able to be done because i had 2 5770's OC'd on this same board 950/1350 lol.

[Liam-McShane]

Any news? If i recall actually, when my 7870 used to get to around 75c it would crash and i would get those weird grey lines and i would have to restart my computer, however my other one would work just fine at those temps. Perhaps one of your cards doesn't like the higher temps like mine. 

 

Maybe your motherboard doesn't like all the power it has to deal with, although this seems unlikely. You say it worked with the 2 5770's but they draw nearly half the power, i think. You also have a pretty power hungry CPU there too and it's overclocked. I'm not too sure how much power your CPU will consume at the frequency but your motherboard only has a 4 pin which is rated for 144w. Take everything i'm saying here with a grain of salt, i'm just guessing lol

[JDB4LFE]

i was able to OC both cards to the same clocks as before on the 2nd slot as well, so im assuming it has something to do with either the motherboard not handling the power as you say or my power supply just cant keep up with all of the overclocking going on....its only 80 plus bronze 850w. i've been looking around and recommended PSU wattage for my pc is around 950w with all of the overclocking im wanting to do. seems overclocking my  6950's are just too power hungry to OC both at the same time. any other suggestions or thoughts are still accepted. considering saving up for better performance/lower power video cards that this psu can handle.

[AMD_Nemesis]

I disagree with this. When i was running 2 7870's i could achieve identical clocks as a single card, although i could be an anomaly.

 

JDB4LFE have you tried testing one card in the number 1 PCI-E 16X slot with the overclock, then trying the same card and the same overclock in the second PCI-E 16X slot? 

Thats why i said usually -_- I can too. on 7770s

[AMD_Nemesis]

i was able to OC both cards to the same clocks as before on the 2nd slot as well, so im assuming it has something to do with either the motherboard not handling the power as you say or my power supply just cant keep up with all of the overclocking going on....its only 80 plus bronze 850w. i've been looking around and recommended PSU wattage for my pc is around 950w with all of the overclocking im wanting to do. seems overclocking my  6950's are just too power hungry to OC both at the same time. any other suggestions or thoughts are still accepted. considering saving up for better performance/lower power video cards that this psu can handle.

If it was Power bsod would usually happen gray lines mean oc is too high those cards dont need more than around 800 watts on a 77watt cpu.

[Liam-McShane]

That power supply should be more than capable when new at least. How long have you had it?

[JDB4LFE]

@ Liam - I've had the power supply since around christmas time, so it's about 5 months or so old now.
@ Nemesis - Yea, the system runs stable until i try to OC my cards. As for it being a 77watt cpu...uhh its 125watt tdp and oc'd to 4.5ghz @ 1.4v lmao.

pretty sure i'm going to call this one out on the crossfire connection not wanting to OC properly. They both OC well on their own, but in xfire it just doesn't run stable. Either way i can run any game without them oc'd it would just be nice is all lmao.

[Liam-McShane]

 "Either way i can run any game without them oc'd it would just be nice is all lmao."

 

 

Yeah, true that. At least your PC isn't on fire or anything, although that would look cool  :P

[JDB4LFE]

Ok, so an update on this issue. I got a wild hair up my *ahem* and decided to see what would happen if i just switched my cards around (something i hadn't done before and should have lmao). The one card's base clock was 820 (was in 2nd slot) and the other was 800 (was in 1st slot and was causing my issues i assume). I proceeded to overclock my cards using MSI Afterburner. I got my gpu clock up to 880 and the memory up to 1300 just on stock volts, but dragging the power bar to +20% (I can't adjust the volts as it is anyway for one reason or another). So, in my final assumption/conclusion, the one card just gave me the finger and the other one gave me the green flag :)

[Darell3]

Oh wow, that seems pretty strange to me.