redtomato
Level 1 (24 points)
Desktops

Q: iMac restarts after 5 minutes of heavy CPU/GPU load and loud fan

Hi,

 

My iMac (late 2012 if I recall) restarts when under heavy load for a certain time.

I work a lot with Final Cut Pro X.

 

Whenever I add clips into an event, Final Cut will copy and then transcode and analyze the clips, and this task is very CPU/GPU intensive (Final Cut Pro X is using OpenCL, hence CPU/GPU). After a few seconds, the iMac's fan starts to be really loud, and seems to reach its maximum speed.

Then after a few minutes of that heavy load, the iMac simply restarts, and the fan slows down and stop. after restarting, everything is back to normal, except for the Warning shown by Mac OS X which says that the shutdown was unexpected.

 

I am pretty sure this behavior is not normal. I don't see why a computer should restart/crash when under heavy load.

 

Note: alternatively, to transcode some clips or movies I have used the excellent software called HandBrake, using CPU-only encoder ffmpeg, and I don't remember having had any crashes although CPU was loaded and FAN was spinning loud too. So maybe it has something to do with GPU ?

 

How can I figure out what's going on ?

Thank you very much.

 

Philiippe

OS X El Capitan (10.11.5)

Posted on May 31, 2016 6:48 AM

by redtomato,Solvedanswer
redtomato redtomato
Level 1 (24 points)
Desktops
A:

For those who find this case interesting, here is the outcome.

The symptoms were caused by a defective RAM chip. The issue wouldn't be detected by Apple's diagnostic software (called hardware test, triggered by pressing D when the iMac starts).

 

The Service support used another software (apparently Apple-provided, too) in the Lab; then they replaced the defective RAM memory chip, and the problem was fixed.

 

After testing the iMac, it wouldn't crash anymore. What's more, the FAN doesn't start so early when the machine is under heavy load. And the global performance (in Final Cut Pro, for instance) are really better than before. It seems the iMac was struggling with the defective memory, using a lot of CPU and producing a lot of heat until the hardware protection eventually triggered a power-off to protect the electronics from burning.

 

I didn't expect the problem to be RAM-related, but it's a good news, because the spare parts are cheap and the iMac doesn't need to be pried open to replace the RAM chips.

 

I wanted to thank everyone for their advice and lineheart.lu for their remarkable service.

 

I hope this report helps.

Philippe

Posted on Jun 22, 2016 11:08 PM

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redtomato

Q: iMac restarts after 5 minutes of heavy CPU/GPU load and loud fan

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  • Helpful answers

  • by Mike Sombrio,

    Mike Sombrio Mike Sombrio May 31, 2016 6:53 AM in response to redtomato
    Level 6 (17,283 points)
    Apple Watch
    May 31, 2016 6:53 AM in response to redtomato

    First try resetting the SMC Reset the System Management Controller (SMC) on your Mac - Apple Support

    If the restarts continue run the Apple Hardware Test in extended mode Using Apple Hardware Test - Apple Support

  • by redtomato,

    redtomato redtomato May 31, 2016 6:54 AM in response to Mike Sombrio
    Level 1 (24 points)
    Desktops
    May 31, 2016 6:54 AM in response to Mike Sombrio

    That is an awesome answer thank you very much !

    I'll try right tonight and update this case.

  • by redtomato,

    redtomato redtomato Jun 15, 2016 12:45 AM in response to Mike Sombrio
    Level 1 (24 points)
    Desktops
    Jun 15, 2016 12:45 AM in response to Mike Sombrio

    Hi,

     

    SMC was reset, and Apple hardware test showed no problem. I expected that, as the problem occurs only after a few minutes of heavy GPU/CPU load, which hardware test doesn't do.

    The iMac was finally brought to Service.

    Let's see what they say.

  • by redtomato,Solvedanswer

    redtomato redtomato Jun 22, 2016 11:08 PM in response to redtomato
    Level 1 (24 points)
    Desktops
    Jun 22, 2016 11:08 PM in response to redtomato

    For those who find this case interesting, here is the outcome.

    The symptoms were caused by a defective RAM chip. The issue wouldn't be detected by Apple's diagnostic software (called hardware test, triggered by pressing D when the iMac starts).

     

    The Service support used another software (apparently Apple-provided, too) in the Lab; then they replaced the defective RAM memory chip, and the problem was fixed.

     

    After testing the iMac, it wouldn't crash anymore. What's more, the FAN doesn't start so early when the machine is under heavy load. And the global performance (in Final Cut Pro, for instance) are really better than before. It seems the iMac was struggling with the defective memory, using a lot of CPU and producing a lot of heat until the hardware protection eventually triggered a power-off to protect the electronics from burning.

     

    I didn't expect the problem to be RAM-related, but it's a good news, because the spare parts are cheap and the iMac doesn't need to be pried open to replace the RAM chips.

     

    I wanted to thank everyone for their advice and lineheart.lu for their remarkable service.

     

    I hope this report helps.

    Philippe