I have a late 2012 27" iMac running El Capitan (10.11.5). It is a 3.2 GHz i5 with 32GB of 1600MHz DDR3, 3TB fusion drive. It's worth noting that as of right now I can't get Graphics/Display information from the System Info tool.

While using the the mac, it randomly powers off. It will not power on again until I have unplugged it for a minute or two.

Within the last 6 months, Apple Genius techs have replaced:

  • Logic Board
  • Harddrive
  • power supply
  • Power supply connector cable (not sure what this actually is).
  • GPU? I don't remember if they replaced the GPU, but one of the last times I had it serviced they deliberately ran a graphics "stress test" for a few hours before letting me pick it up again and the test came out fine.

Here is a portion of my Console log right before the last startup:


My GPU has been restarting a lot recently as well. I can provide more from the gpuRestart kernel logs if necessary.

How do I trouble shoot this issue? I don't see any errors in the Console logs and when the mac starts back up, there is no dialog indicating that it knows it recovered from an error.

Other notes:

  • Hardware check was clean.
  • Identical mac plugged in on the same surge protector and not having issues.
  • Bluetooth is disabled.
  • I am using a USB mouse, keyboard and headset.
  • My mac 'otherwise' feels healthy - nice graphics when playing a game, no UI slowness in other apps, wifi is fast. I/O is fast.
  • I am the only user on this mac, other than the guest account.
  • I cannot correlate shutdowns to running any specific program. I have changed from using Chrome to Safari with no luck. I have been running nothing but Finder when crashes happen. I have also been playing games when crashes happen.

I am trying to debug this myself after countless sessions with Apple support repeating the same steps for an hour only to get to a point where they ask me to take it in to a Genius appointment only to have them say they can't reproduce it.

  • Did you try to reduce monitor brightness to 50% and check whether the mac still reboots? Just a total guess, but it significantly reduces the power consumption and gives quite a lot of extra information on where the problem could come from. It wouldn't surprise me if this would temporarily fix the issue. You can the google further from there. Does the iMac really shut down, or does it just power off instantly? Mar 7, 2017 at 17:16

1 Answer 1


Have you checked your device temperature? I had a similar problem with an old MacBook Pro and it was randomly shutting down because it was overheating.

You can check temperature with SMC Fan control or iStat Menus.

Check on System Monitor the power usage, that's always helpful to check what process can be making your device overheating.

In my case was chrome plus some developer tools that i use at work.

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