PSU or 2nd GPU affecting overclock?

Greebo · 12 Oct 2009 at 11:56

I swapped my PCP &C 860W psu for a Zalmann 750W psu because of the noise issue and also added a 5870, keeping my gtx260 for physx for now

D)

Now I have seen various "claims" that a stable overvolting psu like the pcp&c helps with overclocking but I have always doubted it, until now.

I will be doing some more testing to get to the bottom of this (take one card out etc) but I have this week changed two parts of my system and my 24/7 4.6Ghz overclock is no longer working. In fact it refuses to boot even to the bios. 4Ghz is all that I can get stable atm (not even sure whether that is even prime stable yet as it needs way more cpu voltage than before to even boot :confused:

).

All my saved bios settings for various different overclocks (4ghz, 4.2, 4.4 and 4.6 and I daren't even try 4.9Ghz!) all now fail on booting (won't go to bios)

So do you think the change in psu and/or the power demands of running dual cards would have affected my overclock or is it just a co-incidence? :confused:

Sasahara · 12 Oct 2009 at 15:36

It could be the motherboard not being able to supply enough power to the both cards & the CPU with such a high overclock.

Best thing to do is swap the PSUs and see if the PCP &C 860W runs it at 4.6ghz.

gurusan · 12 Oct 2009 at 15:57

Have you tried removing the 2nd card and seeing if the system boots?

Evil-I · 12 Oct 2009 at 15:57

I guess it could well be due to the PCP&C giving a more stable/ clean supply that you had such a good overclock. As suggested above, I guess just swap out PSUs again first and see if thats the culprit.

Greebo · 12 Oct 2009 at 16:02

Already sold my PCP&C so can't check that anymore

I will try with just one card tonight as I guess my cpu at 1.4v will be sucking some juice.

If that solves it, it will be a dilemma as to whether to keept the gtx260 for physx but be stuck at 4Ghz or just have the 5850 but be able to run at 4.6Ghz again.

The million dollar question will be if it is power related, would a better psu solve it or does the issue lie with the mobo trying to power two cards?

gurusan · 12 Oct 2009 at 16:08

GTX 260 for physx seems silly. better to have some 55nm g92 based card, or maybe one of those dreadfully slow (for gaming, but probs very good for physx) new 40nm GT220 cards

Greebo · 12 Oct 2009 at 16:10

gurusan said:
GTX 260 for physx seems silly. better to have some 55nm g92 based card, or maybe one of those dreadfully slow (for gaming, but probs very good for physx) new 40nm GT220 cards

I know but it's not selling and I am loath to sell it for £80 just to replace it with a £50 card. Hardly seems worth it. And all that physx power might come in handy one day....................

Added bonus is that I always have a decent back up card in case of main card failing.

gurusan · 12 Oct 2009 at 16:13

...but by having anything in the 2nd x16 slot you are also halving the bandwidth to the 5850 as they are now running in 8x/8x.

might be worth doing some testing on physx + 8x or just the 5850 at 16x. but I get off topic...

Greebo · 12 Oct 2009 at 16:50

gurusan said:
...but by having anything in the 2nd x16 slot you are also halving the bandwidth to the 5850 as they are now running in 8x/8x.

might be worth doing some testing on physx + 8x or just the 5850 at 16x. but I get off topic...

I did wonder about that but my vantage results have not being affected running at 8x compared to other people just running a single 5850. But while I have just one card in, I;ll do some comparison checks just out of interest as well

Greebo · 13 Oct 2009 at 13:52

Update lads and it's not good news (so far as deciding on the cuprit that is)

With one card back in, my overclocks are back up although not quite to my best (perhaps the overvoltage and cleaner lines did help with my pcp&c psu???)

However, short of buying another more powerful, quality psu I am at a loss to know whether it's the psu shortcomings limiting me when I have two cards in or whether it's the mobo's problem.

I don't want to buy an expensive psu to find it's the mobo and nothing has changed.

Anybody running extreme overclocks with 2 graphics cards in the same/similar mobo?

I suppose the sensible thing is just to sell the gtx260 and perhaps try a lower demanding card for physx (if I can be bothered to, that is) but I will miss the physx card especially in NFS shift.