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Question

Computer shuts down when stressed

by Scrawny_ / February 4, 2014 8:42 PM PST

Putting the computer under stress (e.g. Higher end video rendering or gaming) causes the computer to suddenly shut down. It doesn't slow down before shutting down, doesn't restart or bluescreen, just goes black. Restarting the computer immediately after this happens causes it to shut back down shortly after loading the desktop.
From what I've read, this seem to be caused by the CPU overheating. I'm running an FX-8320 at around 35c when doing nothing, and going as high as 65c (According to AI Suite II. HWMonitor never seems to show over 60c) when gaming. I'm using the default heatsink that came with the CPU, and have already tried replacing the heat compound.

To get to the main question, is the default heatsink on the 8320 so utterly worthless that it can't keep the CPU temperatures safe, or could this be caused by something else? I already replaced my PSU, thinking that that might be at fault, so I'd like to get a few opinions before I start spending cash on more replacement parts again and end up replacing the entire PC. Again.

GPU: GTX 780
CPU: AMD FX-8320
Mobo: Asus M5A97 LE R2.0
RAM: A single Kingston 8Gb HyperX Blu, 1600MHz DDR3
PSU: Corsair 750W, CS750M

All parts excluding the RAM are brand spankin' new.
If the heatsink clearly is the problem, any suggestions for a replacement would be more than welcome. Preferably a little over what I actually need just to be safe. I'm not really sure what to look for in the sinks other than reviews, so any thoughts there are appreciated too.
I do plan on doing some overclocking. Not looking for the absolute maximum, just going to take it up a little

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All Answers

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Answer
If a system shuts down
by Jimmy Greystone / February 4, 2014 10:31 PM PST

If a system shuts down unexpectedly, it's usually a heat issue, but you could have also tripped a cutout circuit in the PSU. I'd have to double check, but I would think a 750W might be a bit on the low side for a 780 video card and everything else in the average computer, especially if you're working things pretty hard. It might be that the PSU you chose doesn't have sufficient amperage on the +12V rail to power the video card at full throttle. Every PSU has a certain degree of tolerance, usually +/- 5% on every power rail, but if you exceed that, it will trip a safety circuit designed to prevent an electrical fire.

The other possibility is heat. Just because CPU readings are at the high end of normal doesn't mean everything else inside the case isn't overheating. You also have to remember that there's currently no means of directly measuring CPU temp. What they do is stick a thermal sensor under the CPU socket and use that to estimate the temp of the CPU. You'd think AMD and Intel would have integrated some basic monitoring into modern CPUs to tell exactly what the temp and voltages are, but they haven't. But if your CPU is at 65C, odds are the ambient temp of the rest of the case is north of 60C and that can cause other components to overheat, such as the video card or even PSU.

So a good first test is to just remove the side cover from the system and see if the symptoms either go away or at least change after having done so. If yes, then you get the unenviable task of having to evaluate the thermals and air flow of your case. It's not just a matter of adding more fans. To do it well it actually requires some understanding of fluid dynamics as well as basic newtonian physics. Specifically Newton's third law about the equal but opposite reaction. Some people just throw in a bunch of fans aimed at blowing air out of a case, not taking into consideration that for every cubic centimeter of air you blow out of the case you have to pull in an additional cubic centimeter of air to replace it, otherwise you create a vacuum which is puts extra stress on the fans because they have to turn a little bit harder. All of which is just scratching the surface. So you need to think beyond just the CPU because the CPU is not the only part of the computer.

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Amps and fans
by Scrawny_ / February 4, 2014 10:44 PM PST
In reply to: If a system shuts down

The PSU should be pushing 62 amps on the 12V. From what I understand, that should be enough to at least stay stable. About the general heat inside the case, I have a Thermaltake Chaser MK-I, it's pretty darn well endowed when it comes to fans. It's a little crowded inside, though, but keeping a hand close to all the fans, and inside the case in general, it seems fairly cool.

I was advised to try running Prime95 (It draws every last bit of strength out of the processor) and keeping an eye on the processor heat. According to HWMonitor, it got to around 70c in less than a minute, before blacking out, so it sure seems to be a heat problem. The question now is why it goes up so fast. Could a better heatsink keep the heat at a safe level? Getting that high in such a short time seems a little excessive, even under a stress test.

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Re CPU heat....go to frostytech.com and see for yourself how
by VAPCMD / February 5, 2014 9:17 AM PST
In reply to: Amps and fans

much difference a decent CPU HS Fan does over the stock units. You can spend a fortune if you want but you don't have to to get 10-15c CPU lower temps.

You could try reseating the current HS Fan but my preference is to get something that just does a better job at heat dissipation.

Once you get that under control....check other components like the GPU and the chipsets.

Let us know how it works out.

VAPCMD

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As I tried to explain
by Jimmy Greystone / February 5, 2014 10:35 AM PST
In reply to: Amps and fans

As I tried to explain, it's not just a matter of the total number of fans, it has to do with the air flow within the case. The ideal situation is that you're pulling in cool air to replace the hot air being expelled in equal amounts, but that's never quite the case because hot air is less dense than cold air. Your hand is also a very insensitive measuring device. Think about it. We pick things up, sometimes hot things or cold things, all day long. Our hands are calloused and the skin is thick and leathery compared to parts of the body that rarely are touched like the inside of your thigh for example. Out of necessity, many of the nerve endings in the hand are very slow to send signals to the brain, otherwise it'd be like if you trim a fingernail a bit too short and for the next 2-3 days every time something barely brushes past that bit of skin you feel it. Imagine that being the case for everything you touch all day every day. You'd go nuts. Your hand is not a good means of measuring the ambient temp inside a computer case.

A CPU under load at 70C is a bit on the high side, but still within normal bounds. Most CPUs can take up to around 100C or maybe even more, though it's never advisable to test that. But the heat goes up faster in large part because the CPU is working harder. The total number of transistors in CPUs has been going up significantly with each generation, but the total size of a CPU has stayed more or less the same for a long time. The way to accomplish that is to basically shrink the amount of space between different parts of the CPU. Following this thought process to the logical conclusion, you have more transistors crammed into the same volume of space, so it's completely natural that newer CPUs will heat up very quickly relative to older CPUs. You didn't even need active cooling on x86 CPUs until they hit about 100MHz.

So you say you have a case with a lot of fans, which is a good start, but then you say it's "a little crowded inside" which could very well be impeding proper air flow. Air, despite being a gas, behaves like a liquid. If you've ever seen a small creek or stream where some branches or something have fallen in and creates a pool of water behind them, that is what can happen inside a computer case. You get a bunch of cables running all over the place, they're like branches in a stream impeding water flow. The thinner, more energetic, hot air will have less of a problem getting around this compared to the more lethargic and thicker cold air. This creates a problem because heat travels from hot to cold. Hot air is already saturated with heat energy, it's why it's hot, you need cold air coming in to absorb more heat energy from the CPU and other components. If you have a bunch of cables making it so large chunks of that air just sits in pockets around the case you have a problem.

Which brings us back to what happens if you try running the computer with the side cover off?

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What about going with a liquid cooling system?
by Warsam71 / February 6, 2014 9:46 AM PST
In reply to: As I tried to explain

@OP - have you considered going with a liquid cooling system? For example, one of these:
http://www.corsair.com/en/cpu-cooling-kits/hydro-series-water-cooling-cpu-cooler.html

I'm thinking it could help you future-proof, especially if you are planning to do some overclocking. I have a FX-9590, it's a great processor, runs hot; that's why I installed a liquid cooling system right away and have not had any issues.

PS - I'm in total agreement with Jimmy Greystone, very thorough Happy

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