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

Sadly I just experienced my first random reboot under Sierra final build. I was really surprised as I have gone on almost 3 months without a random reboot. I also looked through the logs for the -128 error and did not find any.

Then it seems that it is a different issue.

I haven't read all 20 pages, but maybe we who experience this have something in common?

Like software running? This is clearly not an issue with every single iMac, otherwise it would be in the news a long time ago.

Me, I use the built in firewall but I have customized the rules on the OS level so I run a custom /etc/pf.conf.

Anyone else?

Also I had the logic board and the PSU replaced this summer, so if it's hardware related, I cannot see any component other than the Airport/bluetooth card.

The BT chipset on mine is 20702B0, firmware v118c9123.

The software I have constantly running are iTerm 2, Safari and Outlook 2016

For my case (-128 reboot):

I had a MAC mini late 2012 before, then i restored the mini backup to iMac late 2015.

THEN i had this reboots which i NEVER had before on mini!

(Same external hardware and software)

So there is some kind of combination which MAC model and OS.

Here's my overall activities from this issue (which has solved this issue, so it currently seems).

*Issue - 5k iMac 27" Late 2014 - after updating to 10.10.4 the iMac would go straight to black, no freezing, no advance warning, just off. Turning it back on required physically unplugging the power cord from the wall, waiting 10+ seconds, and then plugging it back in. At times, once logged in [and others on the login screen] it would repeat itself at random and cut to black again, or after a while cut to black again - completely random times.

1) Logic board was replaced - this did not fix the issue.

2) Upgrading to 10.10.5, El Capitan or Sierra did not fix it, neither did downgrading to Yosemite [via Internet Recovery].

3) The Authorised Reseller Technician replaced BOTH the Hard Drive & Solid State Drive [as I had a Fusion Drive].*

This seemingly has solved the issue. I've had it on a couple of days now, with no issues.

*The Technician thought it might have been the hard drive as whilst I was backing up the computer on Time Machine (by playing a video repeatedly so it wouldn't idle or cut out) it literally took an ENTIRE week. Backing up 1.67 TB should not take 7 full days.Whilst I was transferring files back onto the new install after the HDD SSD replacements, the migration of 1.67TB of files took 56 hours, which, when I did the math, checked out okay.

So.... I'm hoping that this now solves other peoples issues. Fusion Drives have been an issue in the past, as I know of, the previous iMac non-retina version also had a HDD & SSD replacement in a worldwide replacement scheme. So it's not an uncommon thought that Fusion Drives may be the culprit we have been looking for.

I doubt I will ever upgrade this again [except for when the new filing system comes in] as Sierra is pretty stable and I don't want another issue like this happening again - I couldn't afford it when it's out of warranty.

Again, I'll repeat, my issue was different to many others here, mine gave no warning and didn't randomly restart. It just cut out. Persist that they fix things, replacing the Fusion Drives would not nearly be as costly as the entire machine, so no doubt Apple will hopefully start there at a minimum. Good luck!

Interesting. How about physically removing the bluetooth/airport hardware from the iMac, hook up a USB mouse/keyboard, and run the machine on ethernet and wait. If it doesn't randomly restart after 3 days, I'd say you're definitely on to something big.

https://www.ifixit.com/Guide/iMac+Intel+27-Inch+Retina+5k+Display+AirPort-Blueto oth+Card+Replacement/30513

I bought my iMac back in December went to Apple and finally got a brand new replacement. For a while I had no issues but recently it has started to restart again, freezing at first. Really don't know where to go from here as I love this thing but spending all this money on a faulty computer is not something I can live with.

Just received my refurb late 2015 iMac 27" (17,1) and guess what, it restarted even during the setup of the OS! Then another 4 times in the next few hours. Makes me think that's why it was in the refurb section 😟

I mainly wanted to say I am very grateful for all of you who have posted. It helps me manage my expectations and has given me some things to try. Here is what I've taken from the thread:

- Some have seen good results from Sierra (I am downloading that now)
- Most only saw results from a new logic board

- Also worth trying trying turning off bluetooth

- Most took months to get that new board, needing to be persistent to say the least

- A video of the restarts might help

I have an additional problem in that the machine was bought in the UK and sent to me in South Africa. They may or may not want to fix it here under the warranty (at least one store said Apple Care did work here even though they are only an affiliate, but I don't have AC just the first year warranty). They might also try to argue it was damaged in transit. They might not even have the part (logic board with M295X) as I haven't seen these BTO's on sale.

Will report back in time of any results.

Sierra has solved this problem for me - so far no random reboots. And it seems to have updated the firmware it is now IM171.0105.B09 so I guess Apple did figure out how to fix the problem without replacing hardware.rateful

Again grateful for this thread - I had actually been planning on staying on 10.11 as I thought it might be more stable!

Same issue with restarts.

Made a clean install on a second portion with El Capitan—restarted while installation process and afterwards.

Today I upgraded this clean install to Sierra ... no randomly reboots since that. When it remains stable, i'll try the solution on my main drive.

Thanks for the lots of information in this thread!

Same as the others Sierra has solved the issue no random restart since installing it last week, stoked!

chrisrobinsonSD wrote:

Same as the others Sierra has solved the issue no random restart since installing it last week, stoked!

I promptly installed Sierra, too, because of the EFI update, but it did nothing in my case: I still have random freezes and reboots in both my Sierra and Windows 10 Boot Camp partition.

My first visit to my local Apple Store resulted in nothing: they kept the computer for almost a week and said that they couldn't replicate my issue and that the hardware was ok.

I can believe them as the behaviour is quite erratic: it can go on without problems for days, then suddenly become a nightmare and rebooting, quite often without kernel panics, several times in a day for weeks.

I lost more time troubleshooting and trying this and that than using the computer; and this is going on since February.

Now Apple Support suggested they send me a courier and they take the computer in some big centre in Milan for further analysis.

I'll update this thread with the results.

Before upgrading to Sierra I had these random restarts at least a couple of times per week. After Sierra I've seen the iMac hit > 20 days uptime.

But I now have a new problem which seems to be a new take on the old one. Same symptoms when it happens. Out of the blue I cannot manipulate anything on screen anymore. Mouse seems normal at this stage, but as I try to click windows and menus it'll change to beach ball. Notifiers in the status bar freezes and all I am able to do is eventually change window focus with a very long delay. (2 - 3 minutes after clicking a window it'll pop into focus.)

Nothing at all is working at this point, and the CPU fans are slowly rising until they are at full blast 10 - 20 minutes after the symptoms first startet. With the old problem, the system would behave the same up to the point where the beach ball started, and then just reboot after a little while.

I've tried scouring the logs to see if I can find anything, but must admit that I've lost interest in the machine at this point. To me this is a tool, a faulty one at that. The dealer will not take it back as they cannot find anything wrong with it, and I am using my laptop more and more in stead.

-KJ

My cut-to-black screen issue continued from my last post about 3 weeks after I had both the HD and SSD (Fusion Drive) replaced. I was doing Screen-Share with 2 Apple supervisors when it cut out. They then suggested a power supply replacement. It's currently in now and so far after 3 days, no issues. But I have been fooled before, and like I said, the HD/SSD replacement took a few weeks until the problem occurred again.

Not the same issue as the majority in this thread, but just keeping people up to date who have the same issue. There's nothing left to replace if this happens again. I'm hoping it won't though. Anyhow, will update if there's more issues, otherwise the power replacement might have fixed it. Here's to hoping.

Cerchiobottista wrote:

Now Apple Support suggested they send me a courier and they take the computer in some big centre in Milan for further analysis.

I'll update this thread with the results.

A brief update as it's been almost a month since I promised some news: had to wait before sending the computer to Milan in order to complete some work.

The computer is still there, has been there for two weeks, and today they told me that they're waiting for a logic board from Apple that should arrive tomorrow.

So seems I'll get the iMac back with the logic board replaced in a few days: I'll update the thread when I have some news on the situation.