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

well the problem is solved without go to service

How ? i just upgrade to OSX Sierra and "all the problems in the post above solved " .

i wait 3 days to see that there is no freeze or restart again before i post this massage .

So try it before going to service

Amir Arama

Israel

My iMac (Retina 5K, 27-inch, Late 2015) arrived in June 2016. It rebooted on the first day. It has been doing so ever since with brief periods lasting several days when it does not. It has been to the local Genius Bar who suggested that my RAM was faulty and unsupported (64GB OWC), which has been replaced twice.

My primary use is VMware Fusion and VMware have diagnosed that the CPU is running an old version of the Intel Microcode. Apple were informed almost immediately, but support staff who promise to take ownership of a ticket are replaced at the drop of a hat and rarely do what is promised, let alone understand what Microcode is. My current support CSO has been with this issue for less than a month but is working on getting engineering to escalate my issue.

I have proof that the microcode on my CPU has a replacement available and have forwarded that to Apple. This is what that looks like (based on a Linux command-line in a VMware Guest):

root@eek:/tmp# aunpack ~/Downloads/microcode-20161104.tgz

microcode.dat

microcode-20161104.tgz: extracted to `microcode.dat'

root@eek:/tmp# modprobe cpuid && iucode_tool -tb -lS /tmp/micro

iucode_tool: system has processor(s) with signature 0x000506e3

selected microcodes:

001: sig 0x000506e3, pf mask 0x36, 2016-06-22, rev 0x009e, size 97280

root@eek:/tmp# dmesg | grep microc

[ 0.555335] microcode: CPU0 sig=0x506e3, pf=0x1, revision=0xa0

[ 0.555369] microcode: Microcode Update Driver: v2.00 <tigran@aivazian.fsnet.co.uk>, Peter Oruba

This thread has 319 (with mine 320) posts from 58 (59 including me) people who are all describing similar things. What I've not seen is a consistent log of what each machine has in common. I've seen posts about different hardware, different versions of the OS and different results and remedies.

Despite my extreme frustration, I'm reluctant to call my machine a lemon, or point the finger at any particular cause and while the support I've received from Apple was less than encouraging and completely inconsistent, as a community we have not actually made it possible to treat our issue as a single issue.

So, here are my stats:

Model Name: iMac

Model Identifier: iMac17,1

Processor Name: Intel Core i7

Processor Speed: 4 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 8 MB

Memory: 64 GB

Boot ROM Version: IM171.0105.B15

SMC Version (system): 2.34f2

System Software Overview:

System Version: OS X 10.11.6 (15G1217)

Kernel Version: Darwin 15.6.0

Boot Volume: Macintosh HD

Boot Mode: Normal

Secure Virtual Memory: Enabled

System Integrity Protection: Enabled

Time since boot: 4:49

Onno

Thank you Onno,

This is exactly my configuration and:

"It has been to the local Genius Bar who suggested that my RAM was faulty and unsupported (64GB OWC), which has been replaced twice."

same story here and even put back the original memories and went back to the Geniuses but same story.

@Amir Arama

Not sure about the others, but I have upgraded, downgraded the OS, formatted and reformatted and reinstalled a fresh macos sierra but works for couple of day and restarts again.

I strongly suggest that you open coupe of application like video or photo editing and stress the iMac for 2-3 hours before you close this case because many times I thought that the issue was fixed but as soon I start working for 2-3 hours straight on the iMac, it will keep restarting again,

Just my 2cents

Cheers

Hello,

I have the same iMac config, and it is the second time I am facing this issue.

The first time was in October 2016, my iMac was shutting down randomly more and more often. I obviously checked everything related to software, logs, reinstall Sierra, install back El Capitan, etc. In the end, AppleCare was of great help, and they replaced the motherboard and power supply in November.

But, 3 weeks ago, it started again.. So, I've done the same software checks, reinstall, etc. As the motherboard and power supply are 4 months old, I suspect the SSD to be responsible. But AppleCare decided to change my power supply again...... Today, a guy will replace my new power supply by a new-new one. What a non-sense. I will have to wait for the problem to happen again and hope that Apple will not change the power supply for the 3rd time... What a nightmare for a computer which should have been bulletproof.

Ok, the guy came to change my power supply for the second time. I asked him why would it be relevant to change it again after only few months (and why not changing another part). He answered that Apple is providing new or reconditioned repairing parts, and that he cannot know if the provided parts are new or not. He told me that it could be definitely fixed on the first repair or on the tenth ! (Depending on the safety/quality of the repairing parts he receive).

So, I hope that you took AppleCare..

Got a hold of clients machine and raced it to the Apple store for a logic board replacement. After 9 days, no random restarts have occurred -- on a machine that would would restart 1-2 times a day. If anyone still has this issue for their late 2015 imac 5k, they have a solid fix for the issue.

In my case, they changed both the motherboard and the power supply in November, but 3 weeks ago the issue came back. Yesterday, they changed the power supply again. No problem for the moment, but I expect to see it coming in few weeks.

I have the exact same problem with the exact same build. It happens to me in Final Cut 3-5 times a day. I spent almost a year on the phone with Apple talking about it and doing tests at home for them, then finally they had me take it into a store. At the genius bar they first told me that my 3rd party RAM was bad ( it wasn't ), then replaced the logic board (literally just because), and then replaced the entire computer with a new one. THIS NEW COMPUTER HAS THE EXACT SAME PROBLEM. It has to be something with this specific hardware interacting with Apple's software.

Is there any way to bump this up so that Apple can fix the issue and stop looking for bad hardware?!?

Just did a quick meeting with a local photographer here, and they have the exact same issues with all four of their iMacs, just not as often as I have with mine.

I agree that it would seem to be something with the hardware combinations here.

Even though I have tested the third party ram quite extensively in a PC, I think I'll have to find some other ram to test with. Just to be sure.

-KJ

Hi folks

Well, I think I'm finally at the end of my journey. My iMac has been back and forth to the Apple Store, and has in turn had the following replacement parts: Main Logic Board; Hard drive cable; Power supply; Rear panel and power inlet (when it started turning off with *no* warning, the *second* visit resulted in arcing detected on the power input pins)

But despite all this (and to Apple's credit they've all been done under warranty), when it began doing the "turn off with no warning, require SMC reset to turn on" trick AGAIN, I went back for another visit, despite the machine now being out of AppleCare entirely.

To my pleasant surprise, Apple decided to replace the machine entirely with a new model, and so far my only 'cost' is my time, the many intervals of no machine and the 16GB RAM upgrade from the old machine that's incompatible with the new version.

Best of luck to those still struggling, but be persistent, polite and persuasive. It paid off for me.

So; the shop where I bought the memory agreed to let me borrow some different brand memory...

jevel$ uptime

9:10 up 37 days, 10 mins, 15 users, load averages: 9.92 11.23 6.87

Never seen above 14 days before.

Going to swap on the other four computers as well. If that fixes things on their end as well I'd say we have enough data to point at the Crucial sticks.

-KJ

I have the exact same problem. The automatic restarts seem to happen randomly and almost daily. The iMac 27 Late 2015 may be in power save mode or in use (gaming, or simply using terminal or browser. The only upgrade made was installing 32GB of memory that runs slightly faster.

I'm glad to hear that I am not the only person with the same issue. I've been thinking of bringing in the iMac to Apple to help diagnose the issue.

I replaced by original Apple 8GB of memory with the following:

G.SKILL Ripjaws Series 16GB (2 x 8G) 204-Pin DDR3 SO-DIMM DDR3L 2133 (PC3L 17000) Laptop Memory Model F3-2133C11D-16GRSL

I'm wondering whether I should try to replace the original Apple memory.

What is the exact model of the Kingston memory you are using including the specs?

I used the Kingston HyperX Impact DDR3L 1866 MHz CL11.

From the Crucial product page I see that their memory is CL13, but when I insert my Mac model in the compability checker, I get this:

This part is compatible! view all compatible parts

iMac (Retina 5K, 27-inch, Late 2015) iMac17,1

Edit: Here's a link to the exact Kingston kit I got:

HX318LS11IBK2/16 - Kingston

-KJ

Good for you for Apple Care. I'm glad you got things sorted out. But that they have some underlying issue that they have not identified, or that they are consistently misdiagnosing and costing themselves and all of us time and money is a serious issue. Especially for those of us not on Apple Care or on warranty. 2 months after my warranty expired my machine inexplicably bricked, and they've immediately jumped on hardware which I very much doubt. Like you, I have a friend who had an issue, was told it was the logic board, then the mother board, then the hard drive cable and power supply, then the rear panel and power inlet, then ended up buying a refurbished machine on a discount. Awful story even for people who have the extended warranty who eventually got a replacement. Chances are your original machine had no hardware issue at all but could have had a file system consistency issue, or memory sector allocation issue. The diagnosis process flowchart, and utilities to me are inadequate or flawed though my expertise is more in maintaining/repairing PCs. Genius Bar seems to quickly want to do a GPU/Logicboard swap after trying a few cookie-cutter things.