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Mac Pro turning off under heavy load

Graham King

Graham King

macrumors regular
Original poster
Mar 27, 2011
161
114
Oakland, CA
I have a 2012 Mac Pro, 12 core, with a GTX 780. When the CPU and GPU are under heavy load, the computer powers off after about 5-10 minutes. I can't power it back on until I unplug it and plug it back in. This is a new problem, my hardware configuration has not changed recently.

I've been monitoring temperatures but I don't see anything crazy high (although I don't know what high is for each of the different sensors). But when I force all fans to max RPM, the computer doesn't have a problem staying on. So I'm guessing it must be a temperature or sensor issue.

Here's a screen shot from iStat just before failure. Any ideas on how I can troubleshoot this?

Thanks

Just before failure.png
 
I haven't had the issue you describe with a Mac, but when I've had it before with PCs, it's always been a power supply issue.
 
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Try watching how much power the graphics card is using under load. In some instances, the Mac will shut down if it is using too much power. The Furmark OpenGL benchmark is good for testing this. In iStat Menu, watch PCIe BoostA, BoostB, and PCIe Slot 1.
 
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And when a GPU gets hotter, it needs more power, which makes it hotter, which makes it draw more power, etc.

Vicious circle. Clear the fan out on the 780. Blow compressed air backwards through fan. If there is anything directly above it, move it, if you have NO other PCIE cards try running it in slot 2 where it will have air flow on top and bottom.
 
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I was finally able to get the Titan X to shut off the Mac like this during the final stage of Starcraft II.
First time it's ever done this. And it ran though the entirety of MGSV without skipping a beat.
Guess I need to use Nvidia Inspector to throttle it at 225W for some titles (did so on SCII and finished the level, no problem).
 
Thank you all for your tips and suggestions. I have yet to take any action but the first thing I'm going to do it open her up and blow out all the fans and other parts and then watch my voltages. Unfortunately, every PCIe slot is occupied (accelsior, usb 3, blackmagic) so I can't give the GPU any more breathing room.

When it happened, my first thought was also the power supply. When I had a G5 Power Mac, the only thing that ever had to be replaced on it was the power supply.

What confuses me though, is another test I ran. Again, I put a heavy load on the CPU and GPU, but this time I manually cranked up every fan to 90% of maximum RPMs. The computer ran for over an hour before cutting off.

Do you think it could still be a power supply issue despite this test? I suppose it could because if I leave the fans on auto, they never even get a chance to rev up to do any cooling.
 
Your temperature looks good, however, the PCIe BoostA current is quite high. As MVC points out, if your 780 runs warmer and warmer, it will draw more and more power. If at some stage, it pull 120W from a single 6 pin, that may trigger the self protection to shut down the machine.

I am not sure if this is your problem, but you may spend some time to monitor the PCIe BoostA reading. From memory, even though the history graph shows up to 18A, but the actual reading was cap at something like 8.99A. I am not sure if this hardware limitation, or software limitation, or if this limitation still there. Anyway, if that reading keep increasing and finally stay at 8.99A, that may be the problem. The shut down protection kicks in at about 120W (10A), if that keep at 8.99A, the real loading may be 9.xA already, which is very very close to (or actually reach) the "shut down limit".
 
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MacVidCards said:
And when a GPU gets hotter, it needs more power, which makes it hotter, which makes it draw more power, etc.

Vicious circle. Clear the fan out on the 780. Blow compressed air backwards through fan. If there is anything directly above it, move it, if you have NO other PCIE cards try running it in slot 2 where it will have air flow on top and bottom.
Click to expand...

You called it. I blew a ton of dust out of the entire machine. And although all my slots are full, I rearranged them so a smaller card is directly above the 780.

Now running max cpu and gpu load indefinitely with stable temps, rpms, volts, and amps.

Thanks much to MVC and everyone who chimed in and to MR!
 
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