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

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

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

So I must have the quickest resolution in this thread. Taking the information learned, I jumped past all the techs directly to Customer Retentions. After listening to what I have to say came back with an offer that wasn't perfect, but satisfied my requirement. She would cover the replacement of the logic board... (well sort of). She did however offer to allow me to purchase Apple Care and have it back dated to the purchase date of the computer. This afforded coverage for today's problem and going forward for over a year. So the $700 repair I was facing cost my only $180 for the extended warranty. I can handle that.

Thanks Apple for working with me...

I have the same iMac and now it's been just randomly shutting down for the few months but now its so bad I basically can't even use it. It won't restart unless I unplug the computer for a few minutes and then it will restart but then after a few uses it will again just shut down...very frustrating when you spend that kind of money on a computer to have it start doing that after only 2 years of use.

I first called Apple Care and they told me to update the OS which we did. It seemed fine for awhile but then it started doing it again. I then took it to the Genius Bar and they ran diagnostics on it and said everything was fine but it obviously was not because once I got home it started doing it again. So I think they may want to rethink the whole "Genius" part of that title.

I took it to a local computer guy and after seeing it do the same thing he thinks that the logic board is fried from getting overheated.

I pretty much don't know what to do at this point. The Genius Bar was useless so I'm not sure if I even want to take it back to them to tell them what the local repair guy said.

One of the take-aways from this extremely long thread is that the issues experienced are not necessarily confined to one particular year model. In reading these entries, it appears several people has similar experiences but were narrowed down to logic board failure.

I have the Retina 5K, 27-inch, Late 2014 model and have had no problems at all... UNTIL.... I have always ran the beta test versions, mostly because I like to stay ahead of what is coming out. But last week, I think around the 19th, Apple pushed macOS beta version 10.12.4 out to the beta testers. I did the update just like any other update not expecting any complications as I already updated my MacBook Air without issue. As the update was wrapping up, I was prompted to reboot, and that is when .................. Nothing else from the computer, dead, and done. Of course it is out of warranty, naturally why would this happen when the warranty was still valid? I called online support and she put me through several diagnostics, that I of course already completed. She recommended I take it to the Genius Bar.

After a few minutes with the tech, he determined my computer needed to be admitted and that the power source was faulty. Keep in mind, I DID NOT have random restarts or other issues discussed in this thread. The only issue that I had that concerned me was the USB ports worked intermittently. So the next day they operated on my iMac and determined the power source what not the issue, but rather the Logic Board had gone out. The tech hem-hawed around possible causes, but things like the logic board and power supply just don't quit working on their own. They die a slow symptomatic death or something catastrophic happens (as in my case).

I don't know what was in that update, but whatever it was, it took out my computer and Apple is saying its my problem. I read more than once in this and other threads, that updates to the OS have led to catastrophic failures leading to a logic board replacement. As a beta tester, am I not doing Apple a favor....? Seems logical to me that 10.12.4 took out my logic board and they should replace it as simple as that. Knowing the OS updates in the past have caused catastrophic failures, there should be NO question.

Armed with the collective experiences gained in this and other threads, I am about to call customer support and try my hardest to get them to cover the repair.

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.

On 10.12.4 I had crashes every two weeks or so, and had almost decided to give up and live with this annoyance.

Then I upgraded to 10.12.5 yesterday, and already have had two crashes of a different kind than the old "boot out of nowhere" I used to see. Now the iMac suddenly hangs. Nothing but the mouse responds to any input, and then it's only the pointer moving. I cannot click anything. All I can do is to reboot with the power button.

This is getting a tad annoying…

-KJ

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.

Since you replaced your ram with the kingston ones, has the problem come back up since? I have OWC ram installed in mine and am wondering if that's the culprit.

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.