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msi 970a-g43 + amd fx 8350, how do i undervolt?

post #1 of 3
Thread Starter 
First of all, i know about the vrm issues, and I know i should get a better motherboard smile.gif
However... i want to use this motherboard with an amd fx 8350 ^^ for a few reasons... and also i am interested if i can get this "project" to succeed. I have added heatsinks to the vrms on the motherboard, and added a good fan that blows cold air directly on the vrms. The vrms should be well cooled. I have also added fans to cool the motherboard sufficiently, and the airflow inside should be good.
So. Let's assume the motherboard and vrms are efficiently cooled, and i have added a better fan for the cpu too, and the airflow should be set up correctly.

Now, as i understand it this should fix the main issue with this board, however using a 8-core cpu on this board will require more wattage than the 125w that amd claims... so some say there will still be an issue running this setup...
I am not going to overclock, i will run the fx-8350 at 4ghz. Now... the big question...

From what i have read i am fairly sure i can undervolt the cpu, and this shouldnt decrease performance, and it should make the components in my computer (mb and cpu) run cooler but still stable, and last longer.
But... how do i go about undervolting?
Do i go to bios and change cpu volt from auto to say.. 1.25? 1.3? And that's it? I am not so sure how to go about undervolting it in a good way with this mobo and cpu. Thanks in advance biggrin.gif
Edited by diskmedel - 3/8/14 at 9:40am
post #2 of 3
Quote:
Originally Posted by diskmedel View Post

First of all, i know about the vrm issues, and I know i should get a better motherboard smile.gif
However... i want to use this motherboard with an amd fx 8350 ^^ for a few reasons... and also i am interested if i can get this "project" to succeed. I have added heatsinks to the vrms on the motherboard, and added a good fan that blows cold air directly on the vrms. The vrms should be well cooled. I have also added fans to cool the motherboard sufficiently, and the airflow inside should be good.
So. Let's assume the motherboard and vrms are efficiently cooled, and i have added a better fan for the cpu too, and the airflow should be set up correctly.

Now, as i understand it this should fix the main issue with this board, however using a 8-core cpu on this board will require more wattage than the 125w that amd claims... so some say there will still be an issue running this setup...
I am not going to overclock, i will run the fx-8350 at 4ghz. Now... the big question...

From what i have read i am fairly sure i can undervolt the cpu, and this shouldnt decrease performance, and it should make the components in my computer (mb and cpu) run cooler but still stable, and last longer.
But... how do i go about undervolting?
Do i go to bios and change cpu volt from auto to say.. 1.25? 1.3? And that's it? I am not so sure how to go about undervolting it in a good way with this mobo and cpu. Thanks in advance biggrin.gif

your are correct. you simply lower voltage and stress test until you find out what the lowest possible voltage is that will not crash.
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post #3 of 3
Simply turning off turbo core will likely drop the base voltage that the chip runs at. When turbo is enabled, the board uses default P-states, when it is disabled, it should drop to the VID of the specific chip you have (usually lower than the lowest Pstate). That will give you a starting point to begin under-volting. The "default" base voltage for these with turbo enabled is like 1.375V IIRC, turning off turbo core could drop this to as low as ~1.325V depending on the binning of your specific chip. Doesn't sound like much but that alone would drop about 10W off the power consumption of the chip and should be guaranteed stable. When disabling turbo-core, you should also disable APM, as it will induce voltage droop that you don't want as part of your under-volting endeavor.

There's always some stable headroom below the VID to account for tolerances in different motherboard designs and some voltage sag. A lot of PD chips will run stable@4.0ghz with less than 1.25V, some much lower still. (My FX-6300 is "stable" @1.175V@4.0ghz [not extensively tested but the few tests I've found that will turn up instability fast had no problems]). Keep in mind, that a voltage setting, and the voltage under load are not always the same. As you under-volt, I believe it's important to run load tests and observe the measured voltage while loaded. Achieving finely tuned clock/voltage settings at any speed depends on getting tight voltage regulation. The worst is a rising voltage under load IMO (too much feedback/LLC) as that will force the use of more voltage than necessary to maintain stability. Adjust the LLC settings as necessary (if available) to achieve the tightest possible voltage regulation from idle to load erring on the side of a minor sag if there is variation.

If you're stable at 1.225V under load, you'll have reduced the TDP of the chip to about 110W under full load, -not bad! (that's approaching sandy bridge territory for compute efficiency at a given performance level)

After finding your low-voltage stability, switch your voltage control to off-set mode and set the offset to subtract from the VID such that you achieve the same voltage "setting" as you found while using fixed voltage. This will allow your chip to use the low power idle states with reduced voltage.
Edited by mdocod - 3/10/14 at 9:23pm
     
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Toshiiba THNSNH 256GB Enterprise RE3 1TB Asus BD combo drive Artic A30 
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Manjaro Linux Samsung 21.5" LCD E2009WFP E2009WFP 
PowerCase
Seasonic G 550W Modular Fractal Design Core 3500 
CPUMotherboardGraphicsRAM
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Hard DriveHard DriveHard DriveHard Drive
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yes CM Seidon 120V SolydK OpenSuse 13.1 
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