Level 1

41 points

iMac (Retina 5K, 27-inch, Late 2015) Randomly Restarts Without Errors

My iMac has been randomly restarting itself (about once a day) when it is idle. Has anyone else experienced the same problem? I found a YouTube video and it is exactly what happened to my iMac: https://www.youtube.com/watch?v=ka7lUIeiH5E

I witnessed it once -- the computer was on (not sleeping) with the display off, nothing CPU/GPU intensive running. I suddenly heard a chime and saw that the computer restarted itself. I logged in. There was no pop-up window. I launched Console and did not see anything unusual before the restart.

More information:

The computer is idle when restart happens. Nothing on the computer indicates it overheats. Display is off (due to inactivity) and fan is quiet.
There is no trace of software shutdown, kernel panic or crash. System log shows normal activities and then a sudden BOOT_TIME entry, as if someone yanks the power cord.
It is not a power failure because the computer should be off if it is really a power failure. "Start up automatically after a power failure" is not checked.
It started to happen after I came back from a trip and upgraded my iMac to the latest Mac OS X five days ago. This computer was purchased last October and I had never seen something like this until a few days ago.

The comments on the YouTube video suggest a total replacement, but I'm reluctant to do so if it turns out to be a software/firmware problem that can be fixed. -- The computer is heavy and the nearest Apple Store is not very close, not to mention the backup/restore efforts.

Thanks

iMac with Retina 5K display, OS X El Capitan (10.11.4), Retina 5K, 27-inch, Late 2015

Posted on Apr 7, 2016 6:45 PM

Top-ranking reply

@owh

Level 1

4 points

Posted on May 19, 2017 2:58 AM

Two weeks ago I replaced the RAM in my machine and am now using 4 x "Crucial 16GB PC3L-14900 Unbuffered 204-pin SO-DIMM"

This gives me 64Gb and the machine - touch wood - has been stable ever since.

I managed to run Memtest86 overnight when I first installed the RAM and it completed 4 entire test cycles with no errors. In addition I've been able to complete the "guaranteed crash" that I used, exporting a slideshow from the Photos application with no errors or crashing.

I returned the 4 x "16GB 1867MHZ DDR3 SO-DIMM PC3-14900" from OWC that was installed when I first purchased the machine.

So, at this time, I can confirm that a 27" Late 2015 Retina iMac i7 can run 64Gb of Crucial RAM.

Hope this helps someone else...

Onno

View in context

343 replies

Sep 13, 2016 10:25 AM in response to Dyslexicant

Upgraded now, let's wait.

Sep 15, 2016 10:02 PM in response to longtom99

3 nights without reboot! 🙂⚠

TJ-Alex

Level 1

4 points

Sep 15, 2016 10:13 PM in response to longtom99

Well thats good news for you. Hopefully when I update my Imac to macOS the random freezes and restart would be gone. I'm waiting for the official macOS update patiently and hope to leave El Capitans unstable update for good.

jwbry

Level 1

15 points

Sep 16, 2016 12:07 AM in response to jwbry

Spoke too soon. Resets have returned. Now running on my old mini just fine.

Sep 16, 2016 12:12 AM in response to jwbry

On 10.11 or 10.12 you have the resets?

Emptynet

Level 1

4 points

Sep 17, 2016 8:17 AM in response to longtom99

Sad news - after the logic board and PSU replacement, my machine has not hung and restarted, but has now *immediately* powered off four times, so I'm back to square one with Apple.

MrFinch

Level 1

4 points

Sep 17, 2016 11:28 AM in response to Jeremy Liu

I am having exact same problem. iMac 27 5K retina and late 2015 model. Standard original configuration. Mouse freezes and then auto restarts after 20 seconds. Aargh!! Has happened on an off for months. Because this is my home machine I don't use it during the day. From this thread it looks like the only thing solving it is a new logic board.

Sep 17, 2016 11:43 AM in response to MrFinch

do you have -128 reboots?

wait for sierra update, mine is stable till now.

MrFinch

Level 1

4 points

Sep 17, 2016 11:51 AM in response to longtom99

Yes I do. I checked in the console. Did you load the beta version of sierra?

jevel

Level 1

4 points

Sep 17, 2016 11:58 AM in response to Jeremy Liu

I have upgraded to the Sierra GM and are waiting to see if the iMac will reboot again. My record on 10.11.x was 12 days. On Sierra I'm now @5 days.

-KJ

Sep 25, 2016 5:24 PM in response to Jeremy Liu

For those of you who have upgraded to 10.12, what are your results?

Unfortunately, I have seen no change. Random reboot behavior persists as it did prior to upgrading to Sierra.

Sep 25, 2016 9:53 PM in response to andrewfromashton

For me the issue is solved with Sierra.

I had random reboots with -128 Error.

StigBull

Level 1

20 points

Sep 26, 2016 1:29 AM in response to Jeremy Liu

Any news on the Sierra update? I have a mid-2015 iMac 27" 5K. Same thing here, the reboots seems to only happens at night when the computer is sleeping.

I had the PSU and logic board replaced this summer, but it made no difference so I'm quite sure it's not hardware related.

Unfortunately I cannot upgrade to Sierra right now because the computer is a DAW, and Steinberg has indicated that Cubase (as well as the drivers for the external audio card) is not Sierra compliant at the moment.

TJ-Alex

Level 1

4 points

Sep 26, 2016 4:50 PM in response to Jeremy Liu

Well its been a total of 6 days since I updated my Imac from El capitan to macOs Sierra. I have not encounter any random freezing and restarts. For me it looks like it was the update El Capitan 10.11.4 and so on that caused those problems. I have only experienced random wierd color pixaled picture when my Imac is shutting down but the computer is still usable. I noticed safari crashed one time with an error so I use Firefox instead. The imac I own is 5k Retina, 27inch, late 2015) 3.3 GHz Intel Core i5, Memory: 8 GB 1867 MHz DDR3, Graphics: AMD Radeon R9 M395 2048 MB bought at Best buy.

MrFinch

Level 1

4 points

Sep 26, 2016 7:57 PM in response to longtom99

Issue appears to be fixed for me too since I updated to Sierra. Going on one week and no issues. Keeping my fingers crossed!

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iMac (Retina 5K, 27-inch, Late 2015) Randomly Restarts Without Errors