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Heatsink placement with universal GPU blocks

post #1 of 29
Thread Starter 
Hi everyone, new member here! Been reading the forums for a long time but never posted. Anyways, I've never watercooled my graphics cards before, but am getting into doing that now. I have two 7870's that I plan to cool, with 2x EK Supremacy Bridge Edition connected Dual Parallel EK Bridge, I am excited to get it all set up as soon as it arrives! I have not watercooled a gpu before, much less used a universal block (my cards are not compatible with the full cover blocks anyways, so not an option, but I prefer universal I think because then I can use the blocks on new cards down the road as well), and so my question is this: with a universal block, I understand that cooling the other components of the card needs to be done with small heatsinks and such. After looking on these forums and others, I am having a hard time definitively knowing WHAT components I need to attach heatsinks to however. I am puzzled because the stock cooler on my cards, (XFX HD7870 CDFC) actually only makes contact with the gpu core itself, and the vram, along with mosfets and all other components only receive the airflow from the fans that are cooling the gpu core's heatsink. Does that mean I do not need to cool these other components, providing I have decent case airflow? Most people say from what I have read that the vram needs heatsinks, and many places I've read that the mosfets do too, however, I am hoping someone here will be able to show me definitively what I need. Here is a picture of my card with the stock cooler removed:


Any input on this would be greatly appreciated. Thanks so much!
post #2 of 29
VRAM / GPU / VRM's
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post #3 of 29
The mosfets/VRMs is what you need to cool. Vram isn't near as important. Leaving the memory w/o sinks won't fry the board. Leaving the mosfets bare w/o any air flow definitely will.
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post #4 of 29
Thread Starter 
ok, so definitely the mosfets/vrms then? Just seems strange to me that they were not cooled by the stock cooler if their cooling is so vital. Better safe then sorry though I suppose in any case. Just to confirm then, here is what I need to cool: Yellow - GPU core w/EK Block Blue and Red: VRAM and Mosfets with heatsinks


Am I missing anything really important?


Also,if it helps at all, here is a picture of my card with the fans and gpu core heatsink removed, you can see the bracket that is attached to the card, and although it does cover over some vram modules, it doesnt actually make contact with them.

post #5 of 29
Thread Starter 
it just seems strange that the components would not be cooled by the stock heatsink and yet do require heatsinks when watercooling? If anyone has has experience (or even just has the knowledge) with this it would be super appreciated! Thanks smile.gif

Also if I do need heatsinks, if someone could point out the components that do require it (i know what the vram is, but I can't say I an expert in identifying vrm's or mosfets :s) that would be great too.
post #6 of 29
Thread Starter 
.....bump.
post #7 of 29
You've pretty much picked out the MOSFETs, So getting some cooling on them would be good. The RAM actually doesn't run that hot, so they should be fine naked - but really, just check them with your finger once its up and running, if they get too hot to hold your finger on, they're getting above 50C, and you can just get some VRAM heatsinks on them, which should reduce the temp on them 10C-20C depending on what size you get. Things will run hotter if you plan to overclock the GPU/memory, if you plan that, I'd definately make sure you have heatsinks on the stuff. But really, the GPU and VRM mosfets are the important bit.

Also the reason most folks need heatsinks when watercooling is A) most cards have thermal pads connecting the VRM / memory to the heatsink this helps cool them, and needs replaced (that's why full cover waterblocks are popular) and B) theres usually a loss of airflow to the chips if they aren't contacting the original heatsink, and therefore run hotter, so heatsinks added mitigate the loss of airflow.
post #8 of 29
I just put my dual 7850's under water yesterday. I only placed some Swiftech MC14 copper heat sinks on the VRAM modules. My VRMs were also uncovered by the stock heatsink/fan. I have a good 140mm fan that blows some good air directly onto the GPUs, and so far I haven't had any problems with any my cards under heavy stress testing. If you have good air flow, you may not need heat sinks, but you can put them on to be safe. I have some Swiftech MC21 MOSFET heatsinks that I purchased, but just didn't put on. My thought was along the lines of covering anything that that had thermal paste or thermal tape on it once I got the stock sink/fans off the card.
    
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post #9 of 29
Thread Starter 
Interesting. Yes the vrm's as well as the vram had no thermal paste or pads or contact of any kind, though I'm sure received some cooling from the airflow of the heatsink's fans. I do not plan on overclocking my graphics cards in the immediate future, however would certainly like to be able to entertain the possibility of doing so should I have the desire to (and I have no doubt I will sooner or later). I do actually have a 120mm fan on the inside of my HDD cages that blows air directly at my graphics cards, as well as a fairly quiet 140mm fan in my side panel that right now is exhausting the air blown onto the cards. Do you think I should make this an intake as well?

I do find it strange that I would need heatsinks on the components that previously were totally uncooled aside from incedental airflow from the heatsink fans (and were fine even when I was overclocking the cards in the past), when with the heatsink removed the case fans I imagine will provide a similar level of airflow over them. But I think that I likely will add heatsinks to be on the safe side, I figure the cost of heatsinks for both cards is less than having to replace one!

So as far as the actual placement of the heatsinks go, I can easily identify the 8 vram modules, but for the vrm's/mosfets, I may need a little help. From my inspection of the card, it looks like there are (three?) mosfets chips for each of the four larger blocks (that say R22 on them), which I believe are the vrm's. Here is a photo where I have circled what I believe to be the mosfets (red) for each vrm chip (yellow).



Now do I need a heatsink on the mosfets (red) only? Or do I need a heatsink on each vrm (yellow) as well?

I apologize if what I am saying in terribly wrong, like I said I've never taken apart and watercooled a gpu before.
post #10 of 29
you only have to heatsink the red stuff - and probably only the pairs together - they are the main drivers that get hot. The yellow parts are the coils - they shouldn't need heatsinks, even though they may get warm. Its the semiconductors that need the heat protection.

now you'll see you've red circled the 4 phases of the VRM and each phase has 3 chips - the two side by side are the main drivers to the coil - they're the ones that will generate the most heat, as they have the most current flowing through them. then just above each pair is the "driver", it basically just boosts the signal from the PWM chip for the FETs, so this won't have as much load on it. So as long as you cover the main pairs, you'll be fine, but it'll do no harm covering the drivers too.

I think your best just heatsinking the VRM's and the RAM, for all the cost of the small heatsinks, it can prolong the life of your card. It's heat that kills electronics. I usually aim to keep stuff under 50C, though most small semiconductors like the VRMs are rated all the way up to 105C in a lot of cases, sometimes more. if you can get me the numbers off the FETS, I could try and find out their rating for you. smile.gif

Edit - OH and you may be best turning that side panel fan to an intake, get some fresh cool air blowing directly over the card, it all helps. I assume you have top exhausts?
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