Thursday, May 01, 2014

Taming the Gigabyte GA-990FXA-UD3 voltage regulator module (VRM)

This is kind of an oddly specific problem and solution, but this is a popular motherboard and I couldn't find anything truly definitive on how to fix this when I searched. Maybe this will help some of you. If you already know the problem and want the tl;dr solution: just run push-pull on your CPU cooler. Attach another fan on the back. That's it. If you want to know why, read on.

The Gigabyte GA-990FXA-UD3 has been through four iterations now. One of the things they seem to keep changing is the design of the voltage regulator module heatsink - and apparently they never get it quite right. At least not for this board's intended purpose; it's supposed to be an enthusiast/overclocker board, but the high VRM temps mean you can't really overclock very far before throttling or other problems kick in. This is the area in question:


The revision 4 board actually has a pretty beefy heatpipe heatsink that's a clear improvement over the revision 3 board, and for many people (especially if you're running stock speeds) it should be good enough.

THE PROBLEM

It's actually twofold:
  • This part of the motherboard is often a "dead spot" in terms of airflow, as it sits between (but slightly below) the CPU cooler and the case exhaust fan. Overclocking usually means a hefiter CPU cooler too, which further isolates this dead zone - all that heat just sits there on the heatsink.
  • This sink is still barely enough to keep the VRM at reasonable temps even at stock speeds. I was getting 91C at full load (running Prime95 torture tests). Overclocking even a little bit - without changing the voltage - bumped that to 94C. And that's in a case with six 120mm case fans, and lots of little holes all over the case for passive airflow. There's just no flow right in this spot.
Temps like that won't fry your system or even lead to throttling (I don't think), but they're not particularly healthy over the long term. VRM chips do have more thermal headroom than, say, a CPU, but I don't like any chip in my system to be running at close to 100C - and if you have a worse case setup than I do, you could even be exceeding that.

THE CRAP SOLUTION

You could do something inelegant like attaching a fan or two directly to the heatsink, or using something like the Antec SpotCool to direct air onto it. I tried just hanging a spare 80mm fan off my CPU cooler to see if directed airflow would really help, and it lowered my full load temp down to 74C at stock speed. That's a 17C improvement - hey, it works! But it's also ugly and sounds yucky, and there's no easy way to permanently attach an 80mm fan in this area.

THE REAL SOLUTION

Go push-pull on your CPU cooler.

I took my bottom 120mm case fan and clipped it to the other side of my CPU cooler as a test. Luckily my Enermax ETS-T40-VD came with extra clips, but a lot of other coolers make it just as easy to attach an extra fan. Doing this, my VRM temps topped out at 81C at stock speeds, and 85C overclocked. That's a decent enough compromise, I think, and should be a pretty comfortable max operating temp for a VRM (remember, these are worst case scenario temps). I'm pretty confident these chips won't die before my next motherboard upgrade, and my CPU won't be throttled.

WHY DOES THIS WORK?

ATX motherboards are pretty much all designed for downflow CPU coolers, because that's what AMD and Intel have used since Intel helped draw up the standard. With the stock cooler, the air expended by the CPU fan ends up being directed through the heatsink fins towards the RAM and VRM before being pulled out of the case:


But with most push-only tower CPU coolers, the airflow is directed too far above the VRM to do much good beyond cooling the CPU - it just goes in a straight line through the cooler and out the case. The extra "pull" fan just helps draw the VRM heat into that flow - it's not so much that it's pushing it directly out, instead it's pulling the hot air in behind it before expelling it out along with the CPU heat. It's obviously not as good as having air directly on the heatsink, but it's good enough. And it has the side effect of helping your CPU temps a tiny bit too, without adding any noise or ugliness to your case. I would bet a fan that "leaks" airflow a bit to the sides would actually be slightly better for this purpose. I'll eventually move one of my TB-Silence fans to be the pull fan on my CPU cooler - these have "ENERMAX" punchouts on the sides that should allow some air through the housing.

(BTW, yes I fixed my RAM slot usage up there - the board's manual confused me. And I've got all four slots filled now anyway.)

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This is increasingly not a blog about Alphabet City, New York. I used to live in the East Village and work on Avenue B, but I no longer do. Why don't I change the name if I'm writing about Japan and video games and guitars? Because New Yorkers are well-rounded people with varied interests, and mine have gone increasingly off the rails over the years. And I don't feel like changing the name. I do still write about New York City sometimes.

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I'm married. I like to travel. I have no kids. I have a house... that I'm bad at maintaining. I used to collect classic video games. I own a lot of musical equipment that far outstrips my ability to use it. When I was younger, I was in a band. I like gadgets, and I'm an Android guy. Someday, I would like to live on a different planet.

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