5k iMac reboots on it's own after installing 10.11.4

For me, by now this has become a daily routine: I start working, at some point my Trackpad 2 freezes, and my Imac spontaneously reboots. I resume working, once my Imac 5K has rebooted and my open windows have reopened. It's quite normal, and yet quite absurd. Meanwhile, I'm practicing patience.

Same problem here as everybody else. Mdi 2015 5K iMac, purchased 18.08.2015.

Swapped the original 8GB memory with 32GB Crucial memory and have had reboots, but only when it's sleeping. It has happened maybe with 3 weeks time inbetween, but it seems to be more often now.

Did run memtest86, left it going for almost 20 hours. No errors on the Crucial memory, but I reinstalled the 8GB original memory yesterday and will leave it running, it if stays up for more than 1 month I know it's the memory, even though it came through clean.

By the way, there's a lot of people complaining about this very same Crucial memory on their forums, with iMacs. If you have Crucial mem, see if you have this model: CT2C8G3S160BMCEU.C16FER

And now, for the 2nd time in two or three weeks, the iMac comes out of sleep, but the display remains off (so does the secondary monitor).

I know it's on and working, I can VNC into it from my iPad Pro, and the desktop shows in VNC just like everything is normal.

Can't find anything out of the ordinary in system.log either.

Now this sure sounds like a hardware failure, right?

system.log may not be the best place to look. The pmset utility can display logs relevant to power management (see "man pmset").

Thanks, I didn't realise pmset had a log option (Ihave only used it with 'assertions' in order to see why my iMac wouldn't go to sleep)!

Are those logs the same .asl data files that are in /var/log/powermanagement?

However it shows nothing out of the ordinary in the few moments before I pressed a key, and untill I powered it off.

Since friday I've had two reboots while the machine was not in use. That means that the downgrade did not solve my issues. -KJ

I can confirm that installing the 10.11.6 Combo Update does not solve the issue. So far, I've had one random reboot, following one of two common patterns: I return to my iMac 5K, finding that it has rebooted on its own.

As of yet, I've not had a random reboot while working on my iMac, with the Magic Trackpad freezing—the other common pattern. As soon as that happens, I'll let you know.

I've had this issue for months now. June 7th, a very helpful Apple Support technician reached out to me by phone from the U.S., looking into this issue.

By now, my patience is wearing very thin, however.

The past few weeks, I've come to suspect that random reboots occur only occur while iTunes (12.2.4.2 and earlier versions) is running, with or without it playing music.

Having updated to 10.11.6, I just had a random reboot while working, following the second of two common patterns: the Magic Trackpad suddenly locks and my iMac freezes, after some thirty seconds the iMac reboots to the login screen.

So, from my experience, updating to 10.11.6 definitely does not resolve the issue.

I just started to post a reply and I got a random restart. Ironic I guess. (trackpad freeze, screen freeze, followed by restart with chime and no error messages displayed) Apple engineer called me earlier today to see if I was still experiencing random restarts and I said I had not had any random restarts since July 16th. Since my last post I tried a few things to eliminate potential causes. I removed the OWC memory sticks (2x16gb) and left the stock 8gb installed. It still random rebooted 4 times the same day 15th June. I took out the stock memory and put my 32 gb OWC memory back in. No restart again until 16 July and then today. I was running iTunes when today's freeze/restart occurred, but had not been running iTunes on any of the previous random restarts. This is first one since 10.11.6 update. So while they are fewer and further between, I am still experiencing random restarts.

Unresolved in 10.11.6

Terry, did Apple Support tell you they are still working on it? I have not contacted support yet and am wondering if I should also contact them so that this issue is more escalated.

I have been working with AppleCare OutReach diagosing my iMac over some time now, but haven't heard from them in about a month now.

I had the last random boot happen on september 1st, but have had some time off work so haven't been using the machine daily.

Upgraded to Sierra GM today, will see if it has any effect on my problems.

-KJ

I also upgraded to Sierra GM on 9/13. No restarts since, but I won't hold my breath. I did find something very odd though. I installed a UPS / battery backup for this new iMac at about the same time I updated to Sierra. I also have it plugged into a USB port and it works with the Energy Saver in system prefs. I have gotten 2 messages that flashed up while I was working, they come and go so quick I can't capture them but msg essentially states “You are now running on UPS backup battery, save files…." or similar, it then disappears within a second. Funny thing is, no other electronic devices in my house are affected by this 'power outage'. I have two electronic air filters that will switch off if the power fluctuates even in the smallest amount (a millisecond brown out, for example). My bellwether indicators... They were still on. So I am assuming this is related to restarts, as others have stated in this and one other related forum, once Apple replaced the Logic Board and Power supply they didn't have the restarts. Is this too coincidental? Or does it give substance to the problem with the replaced components?? I am making some assumptions on how the OS works with the UPS. Anyone with more knowledge care to venture an opinion?

If you have an APC UPS you can install apcupsd (latest version works with 10.11) and see more details on what power glitches the UPS detects. I have encountered many instances where a problem with the house/office wiring or devices plugged in to the wiring resulted in power glitches on one circuit while others were fine. If the UPS is detecting power glitches, start by unplugging everything but the UPS to see if the glitches go away. Compressor (fridges, A/C units) and

laser printers are common culprits.