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

After the 2nd trip to the Apple store, they reformatted but loaded El Capitan 10.11.6 instead of Sierra. Got home and had the same issue. Called Apple Care (for like the 15th time) and they assigned me to a senior advisor who had me download a disk image and run an application. After that was completed used their online services to send the files to Apple Support where it will be escalated to a engineer.

They said I should get a call back in 3-4 days and hopefully they can figure this out.

Here is a portion of the screen shot with Panic Report and Kernel version data which was sent to Apple Support.

I'll join in and bump this if I may.

I own a late 2015 27" Retina iMac. Bought it as soon as it was released so it's just over 2 years old. I too have been experiencing this random shutdown issue for the past few months. It began with unexpected restarts, mainly when the machine was idle or asleep. I'd wake it up to see a dialogue telling me my computer restarted unexpectedly. To be honest I didn't pay much attention to it at first, casually assumed it to be down to a software update or something. Recently it's been shutting down completely with no warning.

I've read tonnes of threads and looked at countless websites to try and get a fix for this issue. I posted my own woes on here a few weeks back:

iMac keeps shutting down randomly

I've still got a years Applecare left and have spoken to Apple twice about this issue. The first time on the phone was the basic sort of advice and was no help whatsoever. Resetting PRAM and SMC etc. Didn't do diddly. Went back to the internet for help. Considered that it could be the power in my flat (it's quite an old building with dodgy electrics). Bought a new power cable for the machine and forked out for an AMC UPS. Unfortunately the UPS broke as soon as I plugged a cable into it but that's another story (I'm in the process of returning it). The new cable didn't make a difference. Tried difference sockets in the lounge, nothing. The machine isn't overheating and is cool to the touch.

After each shutdown the machine won't turn on unless I've pulled the cable out of the back or unplugged from the mains (same as everyone else). I check the console once I've restarted and each time when I search for shutdown cause I get:

kernel: Previous shutdown cause: 0

This relates to a power issue. I suspect the power supply is knackered but after reading this entire thread I'm worried I'll need other parts replacing too. This happens several times a day.

This is my second ever iMac, I owned a late 2009 27" iMac from new for 6 years until the HDD died but that machine spent more time getting repaired than it did on my desk. Love it.

This one looks like it's following suit. Annoying how it's take 2 years to suddenly start playing up but I guess that's technology these days, nothing is built to last, especially Apple products.

Anyway, I digress. I'm booked in to see one of these so called 'geniuses' on Tuesday at the Apple Store, Regent Street which should be entertaining. I live in Central London but don't have access to a car so I'll have to cart this off in a taxi and enjoy my experience in the busiest Apple store in the UK. Joy. At least this iMac weighs a lot less than my previous one, that was a **** of a workout dragging that thing around. Applecare used to collect for repair a few years ago, alas no more.

Would it be wise to wipe my HDD and do a fresh install before taking it in to get looked at?

I'm still running OS X El Capitan 10.11.6. I don't think upgrading to High Sierra will fix this problem from what I've read.

Nice to know I'm part of a big family of frustrated iMac owners.

Cheers

Just letting folks know, I got in touch with Apple Support late November and whined and whined about the issues I was having with my mac. The guy on the phone got me to do all the usual procedures (remove extra RAM, disconnect all peripherals etc, etc) and attempted a diagnostic over the phone. No issues. Told me to get in touch if it rebooted spontaneously again.

48hrs later I was back on the phone where another tech referred me to a local Apple Certified Store The technician there diagnosed a faulty motherboard immediately and replaced it. I had 2 days with it and thought it was looking good. Screen artifacting and glitches all seemed to be gone. Unfortunately I had to go on holidays for 6 weeks and have only now just spent the last two weeks with my "fixed" iMac.

It seems that the problem isn't fixed. I have noticed that the artifacts were appearing again. Like, if I am in Photoshop and rollover the dock, the magnification swell that overlays the app becomes static and as I move the mouse along the dock the magnification effect breaks - I know it's a minor thing but it is indicative of the graphics card not functioning as it should.

The Finder relaunches occasionally out of the blue and sometimes gets stuck and unresponsive. Especially if I try to restart. It also takes about 6 mins for the 7 items in my Login Items list to load up.

And just had a spontaneous reboot. Screen went black for 5-10 seconds and then boots up into the login screen.

I am at a loss what to do. Ask for a new machine (this is already a replacement for my first machine)? Install Sierra and hope things work? Throw mac out the window?

Anyway, just letting folks know. I had high hopes the motherboard replacement would work and it looked good for about 2 weeks but the issues seem to have returned somehow.

Same problem here. iMac (Retina 5k, 27 inch, Late 2015). Started to shut down randomly 2-3 times a day. Called Apple Care and they ran through the textbook software troubleshooting. After 2-3 days of working with them over the phone, they suggested I bring it to the Genius Bar for a tech to look at it.

After lugging it down there and leaving it for a day they could not duplicate the issue and did a clean install of the operating system. Brought it back to the office and spend the entire day reloading apps, etc and about 5 hours later it started shutting down again.

I called Apple Care again and they set another appointment with the Genius Bar, so here I go again.

Same here, iMac (Retina 5K, 27-inch, Late 2015) Randomly Restarts Without Errors, I have formatted multiple times and did a clean install of macOS Sierra 10.12.3 (16D32), still same problem, as usual Apple store Guinness are clueless.

Anyone has any suggestions?

Thanks

I really, really feel your pain. After I posted the above rant I contacted Apple Support last Thursday and went though the usual diagnostics with the support guy who then asked me to try and work in Safe Mode for 24 hours to see if the random reboots occur again. Pointless.

We booted into safe mode and after the horizontal bars effect kicked in I opened Chrome and was presented with a beautiful glitchy screen. Here's a 30 second youtube clip: https://youtu.be/QGt1nGy8yVI

The support guy said this shouldn't be happening and elevated me up to... a higher up guy, who said this was definitely not normal and we should move onto more drastic measures, like wiping, reformatting and reinstalling the OS. This did seem drastic. I told him that I was fundamentally sick of this lemon and that the only process I wanted to go through now was to get either a new machine or a complete refund. He said that he understood my frustration (ha!) and that we had a number of steps to go though before "bringing it to that level". Fair enough.

I was told to get a hard-drive and do a Time Machine backup and we would commence the reinstall. I asked if I could just use one of my existing backups, and was told no, that the backup would have to be reformatted as well to prepare it, etc, etc, etc which I thought was overkill and a waste of time, as I now had to purchase an external and wait for the Time Machine to perform the backup.

The dude said he'd ring back in 24 hours and go through the steps.

24 hours passed, the external was purchased and successfully backed up to and a completely different person rang and I had to bring them up to speed with the situation. We went through the preparation steps, (recovery mode, disk utility, etc) and then he asked me to click erase, which I did, and boom, the erase failed because "Core Logical Volume not found" or something to that effect.

This freaked the high-up technician who said he has never encountered that before, put me on hold for 10 mins and then came back saying that it looks like a hard-drive failure and that I should take it to a repair store and have them look at it "immediately".

Which I did, the next morning, to the same guys who replaced the logic board a few weeks earlier. I explained to them that all I was there for was to have one of the techs confirm that there was a hardware fault and that they were to get in touch with this higher-up guy to establish what was wrong. The kid behind the desk seemed to take all this onboard but somehow none of this information was given to the actual tech who looked at the machine.

Who spent 2 whole days diagnosing that one of the 16GB RAM modules had a fault (and this obviously explained every issue I was having) and because it was third-party materials wasn't covered by my warranty. I explained that I had these issues before the RAM was put in and that all they had to do was try and reinstall the OS and see the error that I had brought the machine in for.

I was told that the installation of software wasn't covered by the warranty and that I would have to pay the charge to do that.

Meanwhile, they finally get in touch with the senior Apple Support "higher up" guy who, incredibly, bizarrely, somehow supplies them with 3 diagnostic reports dated 4 days AFTER I dropped the mac into the repair shop that, inexplicably and unbelievably, corroborates their diagnostics that there is a memory module damaged! I don't know how that is possible.

I drop into the store yesterday with the original Apple 2x4GB Ram modules when all this comes out and, so I am about to go loco on this poor hapless uber-geeky kid when a senior tech comes out of the back of the store, listens to my case and then, like Winston Wolfe, comes up with a plan to solve all the issues.

He's taken the diagnostics on board, is removing the modules, reformatting and testing the mac and will let me know if it is fixed or bust. Hopefully later this afternoon.

If I get an iMac back that is finally fixed (I will not believe it) then fine and dandy. If it is an Apple hardware issue than I can only guess at what the outcome will be.

I am not looking forward to THAT round of negotiations.

Apologies for all the extraneous information. I just need to get it down in writing so I can be clear on the hoops I have had to jump through. I could have done the reformatting all by myself. I kind of didn't want to go down that route but when an Apple Genius tells you to do something...

I also have the same problem of it randomly shutting down. Mine is a late 2015 5K retina. Just like you I also removed the factory RAM for OWC ram so its interesting to note its not the RAM.

Currently I'm on El Capitan. After trying Sierra for a bit, my 5k would randomly start glitching and on the shut down I'd often get a fuzzy pinkish grey screen. The bottom line is, I think you may be right about a whole batch of monitors perhaps were sent out.

Apple engineer reviewed the panic reports and determined that there was a "damaged index." I worked with a Sr Advisor with Apple and they walked me through the steps to repair. After waiting 24 hours letting the reindexing to take place, it appears to be working correctly. No shut downs for over two days.

The bad news is that I have a Airport Time Machine which is my wireless router and Time Machine backup. The Sr Advisor wanted me to reindex this as well by physically connecting it to the computer however I could not disconnect wifi for 24 hours so we bypassed this step. When I turn on Time Machine for a back up the computer begins to shut down again.

It appears the damaged index was the issue as the Time Machine apparently still has the damaged index.

Hopefully this helps some of you to troubleshoot.

A full week later and no shut downs. The corrupt index was the culprit and so easy to fix. To bad it took Apple 3 weeks of basic troubleshooting and several trips to Apple store lugging my computer around to get to this point.

As for the Airport Time Machine, after calling Apple Care back and taking to different Sr. Tech, he said there was no need to physically connect my Time Machine to the computer to have the back up reindexed. He spent under 10 minutes with me and it was fixed.

Apple Tech was adamant that I needed to pull the unit from my electronics stack and physically connect to my computer with eithernet cord. I call back and talk to someone else and they have a different solution. The one thing I have determined through this whole ordeal is that Apple Care Techs are reading from some "How To" manual and not much help. You need to talk to a Sr. Advisor or escalate to a Engineer.

Thankfully this is over and good luck dealing with Apple if you need any help.

Ugh, this is unbelievable..

I Indexed all drives and still this pice of junk keep restarting in middle of the workflow, can't believe the most expensive iMac on the planet it is simply a pice of junk. If this happening to a $5000+ iMac and Apple has no idea why this happening except keep asking to book appointments and drag this iJunk to the store to waste more time and money , I can only imagine whats happens to a cheaper model. Shame on you Apple that your entire focus is to get only new customers and totally abandoning your loyal customers of decades, first the MBP 15" 2009 logic board without replacing it, right after that was the MBP 17" 2011 graphic/screen flicking issue and now this ... Shame!

Its unbelievable

i have also the same problem of random restarts & freezes for more then two weeks .

After reading all the people posts hear , its clear , that there is a defect in the 27" Retina late 2015 .

I don't know if other version have the same problems , But Apple should face with this problem ,

Since its shear a lot of frustrating costumers that paid a lot of money to buy "the bast & expensive computer in the world ".

i expect from apple to solve this problem with apology free to there loyal costumers .

i will go with my IMAC to apple store and will tel them about this defect , and if they not replace the defective parts

free , based on this there'd i will go to court !

Amir Arama

ISRAEL .

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.