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

Apple's canned response, "The logic board replacement may have solved the issue on their computer but we don't know if their machine is restarting for the same reason as yours. We need to run more tests before we can determine if it is a hardware issue or software issue."

It is a $300 part we are talking about here and this would significantly cut into Apples $624 billion net worth.

I was having a similar problem, but it would just power off, not restart. Took it to the Apple store. They wiped my computer clean and re-installed the OS. I took it home and that didn't fix it. Took it back and they said it was the RAM, so I ordered all new RAM. It worked for a week or so, then the problem came back. I took it back in, they replaced the logic board and the power supply. That didn't work either. After a couple months of back and fourth taking it to them they finally realized they couldn't fix it and just gave me a new iMac. I'm considering selling this one and getting a different computer because I'm not confident that I'm not going to have more problems with it. Even before this issue I was having tons of problems with the computer and had it replaced once before and then the display replaced. It's a shame, it's an amazing computer, and the most expensive computer I ever purchased, and I've never had so many problems with a computer before. I had to buy a second mac because of how often this one has been in in the store for repairs.

I have to say, I read your post and, despite being INCREDIBLY skeptical that this is a software issue, was increasingly filled with optimism throughout the day as my computer, which NEVER goes more than 6 hrs without a freeze/restart was humming uninterrupted for 12+ hours as I worked on a mammoth project. Hallelujah!, I thought. Maybe it was just the Flash extension wreaking havoc as a background process or something and the update cured all.

And then, of course: freeze/restart. This seems to be the pattern: Every time I've taken it into the Apple Store, or done clean-up/maintenance/reinstalls on my own, the problem will seem to be ameliorated. For a spell. Then it returns, and eventually returns to the same pattern (Every 3-4 hrs, sometime occurring in little clusters every 45 minutes.) That might just be randomness tho, that I'm imposing a pattern on.

Regardless: for me at least, not the Flash player. As always seems to be the case, potential solution is presented (not criticizing you, ReynoldsYoung, any suggestion is of course welcome), and it kinda maybe seems to make things better at first--maybe?--and then problem returns. Whatever it is, it is deep deep deep in the computer.

-Jon

I posted on here twice.

Had all this exact issue happening to my iMac.

The second time I took it into the apple store, they replaced the logic board.

Computer has not restarted since. It's been a week and a half, and it's working like a normal computer, and it feels great.

I recommend RECORDING your restarts, and when you have time to bring your iMac in, show them the videos.

I was able to email them to some one who was working on my computer, when I showed the guy at the genius bar.

Record the restarts, and kindly suggest a new logic board. Get a working iMac. (hopefully mine stays working)

Good luck.

YMMV but when I took my iMac to the Greensboro NC Apple store they kept it for a couple of days, saw the restarts in person, replaced the logic board and I got it back in about a week (Apple store is about 1.5 hours from me.) That was first week of June and it has been on pretty much non stop since with NO restarts. I know I was fortunate for the genius/tech guys to see the restarts in person but let's be clear, replacing the logic board on my computer fixed the problem. Period. Good luck.

Every time I got my computer back it worked for a few weeks, even a month once, but always failed eventually. Hopefully that is not the case for you. But I would recommend leaving your computer on at night for a while so if it's going to happen again, that may speed up the process. The last thing you want to happen is for it to work for a while and then fail after your warranty runs out.

Been having the same issue for months now (restarts multiple times a day all random), went to Apple support after escalating to Engineering sending log files, etc…they plainly just told me it was my upgraded RAM. Well suffice to say it wasn't after reinstalling OS X multiple times, going back to stock RAM, wiping the entire machine and starting from scratch…last night I unplugged both of my external Samsung 4K 28" monitors (u28e590d) magical no more restarts after over 14 hours, as soon as I plugged both of them back in within 30 mins or so freeze & restart.

My question to everyone else out there are you guys running multiple monitors? I was told this particular setup which was completely maxed out from Apple when I built it would be able to handle two large 4K externals?

My machine specs:

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

4 GHz Intel Core i7

40 GB 1867 MHz DDR3

Macintosh SSD

AMD Radeon R9 M395X 4096 MB

I'm not running any external monitors but my USB ports are maxed out with peripherals: an Apogee audio interface, 2 large external drives and then a hub with various little things (MIDI devices, printer, etc.) running into it.

Someone on this site looking over crash/diagnostic info said that Apogee stuff was popping up around some of the crashes but it was unclear if that actually a cause or simply a symptom.

Greg Kucharo, dunno if you're still reading this thread, but you seemed to have a perspective about this and knowledge about the inner workings of the iMac that was useful, and you seemed convinced, if I remember correctly, that this issue is somehow connected to a power failure/power issue (the lack of any system notice at the moment of crash, like the power cord was yanked out or something, makes me subscribe to that theory as well.) Any of the ports connected to peripherals supply power and are gonna be connected to the power system, yes? Could it be some deep firmware issue with those ports having some miscommunication with the main power supply system and messing the whole system up? Just spitballing.

-Jon

I've got the following plugged into my USB ports:

Samsung 250 GB SSD

Logitech Performance MX Mouse

Standard Apple USB keyboard w/number pad

So there's still on open one but I'm also wondering if its a power issue that would also make sense, I'm pretty sure this 4GB video card is capable of powering the 5K and (2) 4Ks but then again I could be wrong?

It seems like a power problem, but I could be wrong. The abruptness of the shutdown and the lack of ability of the OS to log anything would point seem to point there but it could be a bunch of other things.

FWIW, I am running a very stock system. No external peripherals, hardware wise it is exactly the system I ordered from Apple. My keyboard, mouse and trackpad are all Apple. I have very few applications I use regularly and some of them are not installed via the Mac App Store. Curiously, the Ghostery Safari extension that Apple asked me to uninstall was installed via the Safari Extensions Gallery. I am assuming those extensions are vetted in the same way as Mac App Store apps and have to run in the sandbox, etc.

I just say again that what seems like the same problem may be the same result with all different root causes. This may be why Apple is replacing logic boards on some and not others.

Just got off the phone with Apple and after almost 3 months of going back and forth with them they're finally having me take it into the store for a test and hopefully replace the logic board there or order me a new setup. I can't take it in till next Friday however I'll make sure to post back the results.

Just talked with my advisor and the engineers are now suggesting that I uninstall Fantastical. I'm going to do that and see what happens. Previous suggestion was uninstall the Ghostery Safari extension, so clearly they are methodically going through every non-Apple thing looking for a culprit, without my doing a full reinstall of the OS.

I asked about the logic board replacement, but there was nothing in the logs that would indicate a hardware issue at the moment. YMMV.

Just another update on my iMac 5k:

Per the request of the engineers, I uninstalled Adobe Creative Cloud AND Google Chrome––within 45 minutes, the computer randomly restarted, again with the error -128.

This has been occurring now for almost a month (looking back at the restart records, which I started keeping going back to June 22nd)

Again, I'm crossing my fingers that I'll finally get the correct fix: replacing the logic board.

I'll just add my story for all those reading this thread. I've been wanting a 5k iMac for a while and have been really worried about purchasing it for this very reason. I ended up making the purchase. I received my computer (fully maxed out in every way, 512 flash drive) about a week ago and have been running it hard (creative cloud, final cut, resolve, etc.) ever since and it hasn't reboot once on me. It came to me with 10.11.5 installed on it.

I know this doesn't really help anyone that is having a problem.. but I wanted to share my experience anyway in case someone was in a similar situation wanting to purchase the 5k iMac.

Good story to have here! I think the iMac 5k is a fine machine––my prettiest and most powerful Mac yet. My employer is ordering one for our office use (my iMac 5k is both a personal and professional machine in my home studio) at my recommendation.

For three months, my iMac 5k it was running 110%.

What seems to be the problem is that something in 10.11.5, in certain machines, bricks critical hardware components in certain iMac 5ks.

And that's the really scary part of this whole thing, because Apple has now designed both their mobile OS and their Mac OS around the idea of constantly updating your software. The fact that a software update bricked hardware is thus a really frightening one.