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 Post subject: Overclocking XFX 6850: PCB incredibly hot!
PostPosted: Sat Jun 11, 2011 11:05 am 
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Location: Germany
Hi, I have been overclocking my XFX 6850 to play Witcher 2 today. Following the anandtech overclock article: http://www.anandtech.com/show/4002/amd-radeon-hd-6850-overclocking-roundup-asus-xfx-msi/8, I have overclocked it to 940/1200 on 1.172V. Then, I ran MSI Kombustor (similar to Furmark) for 15 minutes, core temps never crossed 60C, no glitches. I couldn't figure out how to check VRM temps (GPU-Z and Everest gave some weird results that are too low), so I checked it with a finger :mrgreen: . The VRM heatsinks were warm, but that's it. What has really bothered me that the PCB itself was superhot - I could not even hold my finger on it and nearly burned myself. The cooling is more than adequate: the core was <60C and VRM heatsinks only warm.

Question 1: is it bad?
Question 2: I have a lot of spare small heatsinks left from Accelero S1 cooler, maybe I should just install them directly on the PCB (on the "back" side of it) to cool it?

Thanks for your input.

P.S. I have little clue about overclocking, I just set the parameters as stated in the article, which pretty straightforward to do with MSI Afterburner/Kombustor.


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 Post subject: Re: Overclocking XFX 6850: PCB incredibly hot!
PostPosted: Sat Jun 11, 2011 2:26 pm 
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Joined: Sun Nov 09, 2003 7:18 am
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Location: UK
Hi Anatorax, over-clocking your card, especially with raised voltages, will make it draw more power that will make the VRMs work harder and run hotter.
With modern high power cards cooling the VRMs can often be the biggest challenge. ThermalRight make some great VRM coolers with heatpipes, but they are fairly card specific and only up to 5 series but sure I saw something with a mod to fit 4 series on 6 series card, will look for it again...

My GTX260 is running after-market cooling and at one time my VRM cooling wasn't great, I measured the temp of the PCB on the back of the VRM at 85C! The thing ran folding@home for weeks like this with no issues, in fact my attempt to improve the situation proved worse :oops:

I think SPCR reviews talk about card shutting down at 135C VRM temp but if thats the cut out I'd suggest aiming for say not more than 120C for VRMs under normal use. Furmark isn't normal use!

Seb

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 Post subject: Re: Overclocking XFX 6850: PCB incredibly hot!
PostPosted: Tue Jun 14, 2011 2:56 am 
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Location: London
SebRad wrote:
With modern high power cards cooling the VRMs can often be the biggest challenge. ThermalRight make some great VRM coolers with heatpipes, but they are fairly card specific and only up to 5 series but sure I saw something with a mod to fit 4 series on 6 series card, will look for it again...Seb


boost posted this link over in my thread. Is it what you were thinking of?

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 Post subject: Re: Overclocking XFX 6850: PCB incredibly hot!
PostPosted: Tue Jun 14, 2011 3:33 am 
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Joined: Wed Jul 12, 2006 10:29 am
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Lukewarm VRMs shouldn't be a problem.
MSI Kombuster, like Furmark, is a stress test, which your card passed if you ran it for more than a few minutes.
How hot is the card when play a game?
If the PCB gets extremely hot when you play a game I would consider lowering the voltage. Random heat sinks will only cool down the spots they're attached to, not the entire board.

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 Post subject: Re: Overclocking XFX 6850: PCB incredibly hot!
PostPosted: Tue Jun 14, 2011 4:57 am 
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Joined: Mon Jul 16, 2007 2:35 pm
Posts: 808
Location: Greece
Quote:
Question 1: is it bad?
Question 2: I have a lot of spare small heatsinks left from Accelero S1 cooler, maybe I should just install them directly on the PCB (on the "back" side of it) to cool it?


1. While the vrms don`t seem to be too hot, excess heat on the pcb could lead to problems, wearing out solder points or damaging other, secondary components.
2. You could do that, in fact many cards have a metal backplate that works as a heatspreader for the reason mentioned above. One issue is that the thin adhesive film on the spare heatsinks won`t work very well since the pcb surface isn`t flat. You need a thick, soft thermal pad for this job, no idea if it`s possible to buy such a thing though. Perhaps you could find one by cannibalizing another heatsink.

Another solution would be to simply use a low speed fan blowing on this part of the pcb, not the most elegant but still a solution.

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