5k iMac reboots on it's own after installing 10.11.4

Do you know if there is a way to make Apple aware of it? Is it possible to file a complaint/report without making an appointment and bringing in the iMac? The reboot is getting annoying... I wonder why few people are complaining about this. It can't be just a handful of iMacs that get affected. Maybe most people just turn their computers off every time after they use them?

I have had my iMac back now for a week after replacement of logic board and power supply.

The testing by an Authorised Service Provider definitely showed a hardware fault, but they were unable to specify exactly what that fault was.

I have so far had no further problems, but time alone will tell.

I had restored OSX 10.11.3 before they took the computer in and I was still having random restarts from 5 minutes to 12 hours.

I have since updated again to 10.11.4 which would also have installed the firmware update on the new logic board with no adverse effects so far (remember that if on the previous board 10.11.4 installed the firmware update then going back to 10.11.3 would not have solved any firmware-related problem, since you cannot undo a firmware update.

Since I have a new logic board and no problems with the 10.11.4 firmware update this time round, then that should probably also rule out a firmware-hardware problem causing the crashes.

I am still more convinced that the issue is a graphics related one (the restarts do not always seem to affect the OS, since the screen often comes back exactly where it left off with no genuine reboot or login involved... plus the AMD GPU is on the replaced logic board). What we don't know is whether people getting the logic board repair are getting upgraded hardware, which might confirm the issue.

"I hope Apple is aware of this issue", you say.

Well, I have since received an Apple survey asking about my level of satisfaction with the Authorised Service Provider, which luckily allowed me to express any issues relating to the repair - I therefore used the space to tell them of the excellent repair service, BUT also told them that there had not yet been sufficient time to confirm that my support Case had been fully resolved, together with the fact that at least a dozen other people were still in the same situation, plus the fact that I had already now had two repairs within four months of buying a top-of-the-range computer (the other was a new £350 display after just 1 month!). This did not give me any confidence in, or guarantee regarding, current quality standards: this was the first time in 30+ years of using Apple Macs that I had had any issues with either personal or faculty hardware. I suggested they should be more clear and honest with their customers about this issue.

I am therefore sure in my own mind that somebody at Apple quality assurance is fully aware, as is the Authorised Service Provider whom I provided with all the technical evidence so far.

I can only say that others really must raise an Apple Support Case on their web page by getting them to phone you at their expense and insist that you are fully aware that quite a few others have the same issue on the Apple Support Communities site and therefore at the very least a logic board replacement is in order. You will still have to take your Mac in or get them to arrange with your nearest Authorised Service Provider to test the machine to allow this - only then will you get necessary support.

Waiting for 10.11.5 to come along does not seem to me to be the correct 'consumer' response to this quality issue, especially given such an expensive machine.

You wouldn't wait for the next engine replacement if your car kept breaking down for no apparent reason!

Have not had a reboot since I stopped using Safari the last time I rebooted (3 days 5 hrs ago) as I said I would try in my earlier posting. Will continue to monitor, but so far so good. I had issues with Safari freezing my older iMac. Using Firefox at the moment without any reboot/restart. If this works for the next week or so without restarts I will start loading up the Graphics processor with open apps, run 4k movies on QT and FCP etc and see if the restart occurs again. If not, I'll try Safari again and see what happens.

Today, I tried not using Safari at all but it made no difference. It already crashed and restarted 3 times today.

So for those who have their logic boards changed, can you say that it definitely fixed the problem? I may have to insist that my service provider do so as well.

Hi together,

since a few days the behavior changed: the imac freezes without rebooting itself. You have to hard power off the machine. Mostly it occurs during the night, when it's not used. This changed my opinion - perhaps it is really a hardware fault? But what i don't understand - why has all this started with OS X 10.4.11 - this is that pleads for an software issue.

Well right now im a little helpless - i spent a lot of money for a computer that's not really reliable. The phone call with the apple support didn't help me. So what's next? How can Apple be motivated to fix this issues - no matter if software or hardware-related?

I have also had the same problems with unexpected reboots. Here is my story.

iMac 5k retina worked fine until upgrade to 10.11.4.

Then one day I was working and the iMac froze and the rebooted to the login screen; NOTE not a kernel panic NO message about the reboot.

This happened several times for the next several day, so I took it to the local Apple Store. They checked it out and said they could not find a problem.

So I took the iMac home and 2 hours later it happened again.

So I started to document the problem with the Console app and screen shots.

Every time there was a unexpected reboot I would use Console and search for "BOOT_TIME" and then take a screen shot ( this will give you the time of the reboot).

Then in console I search for "Previous shutdown" and look at the error code and take a screen shot; normal shutdown is 0 or 5 and what I was seeing was -128.

Lastly, I would open a Terminal window and do "last reboot" to show the list of reboots.

After several days of doing this I went back to the local Apple Store and explained the problem still existed and showed them the screen shots.

I made sure they understood it was not a kernel panic and that no messages appeared on the screen about the reboot.

They took the machine and after a week returned it with "new logic board and memory".

The key point for me was having the screen shots and having them understand that they had to use Console to detect the unexpected restarts.

Just to add to the thread (and update), after I reset the SMC, my iMac was fine for 5 days until an unexpected reboot occurred - as always while the machine was unattended. Next was installing the combo update of 10.11.4. Machine was fine for 6 days until I got the now usual unexpected reboot. Next was setting the energy saver control panel to defaults (the only difference I remember from default was that I unchecked put hard disks to sleep). Machine was fine for 6 days until another unexpected reboot. So all in all, in my experience, the unexpected reboot/previous shutdown cause -128 issue appears to take several days to manifest itself when taking steps to attempt to resolve, i.e., reinstalling software and so on.

Pretty frustrating that the issue traces itself directly back to the 10.11.4 update and no end-user remedy seems to resolve the issue. So here we are. Waiting with no assurance that the issue is even acknowledged by Apple or whether the next update will resolve it whenever they get around to pushing it out. In any event, without any confidence at all that it will do any good, I sent a bug report via Apple's feedback page. I've been a Mac user since day one (yes all the way back then) and this (as well as other far less serious OS issues) is by far the worse that Apple has ever put its name to.

Since I've updated to OS 10.11.4 my iMac (Retina 5K, 27-inch, end 2015, 3,3 GHz Intel Core i5, 16 GB 1867 MHz DDR3, AMD Radeon R9 M395 2048 MB) randomly reboots several times a day. Without any sign or warning, the screen goes black and my iMac reboots.

Currently I'm only using Chrome, not Safari. I've tried all the routine checks, repaired permissions, reset the SMC, reset the P-RAM, rebuilt the volume directory from a Techtool e-drive with DiskWarrior, all without success.

I've installed the original update to 10.11.4 through the Combo Update, and have re-installed the Combo Update several times, to no avail.

My advice to all of you experiencing unexplainable reboots: Please take your computer to an authorizied Apple repair service shop, because this is clearly a hardware issue. Apple wouldn't be replacing motherboards and/or power supplys if this was just a software issue. I got my motherboard replaced, so did my friend here DocLaban, and also several others both in this forum and elsewhere. And the problems with reboots are gone after I got the new motherboard. The hardware issue and the reboots may have been triggered by OS X 10.11.4, but it's still a hardware issue, and I'm pretty sure time is wasted if you hang around waiting for OS X 10.11.5 hoping that might solve the problem.

Sending in your computers with a full description of the problem, and referring to all of us that have had their motherboards replaced, is also a far better way of making Apple aware of the extent of the problem than just posting here. My two cents...

Cheers,

Eivind

Hi all

I have an iMac 5K 4GHz (late 2014) and had after upgrading to OS X 10.11.4 been struggling with daily problems similar to those described in this thread:

1) Random screen freezes followed by an automatic restart (the dreaded "previous shutdown cause: -128")

2) Some freezes and blank screens that required a manual (hard) restart and showed the white kernel panic text when restarting

3) Random occurrences where the Mac would suddenly log me out and show the login screen while I was in the middle of working

1) and 2) could both occur while I was working on the machine and while the machine was "sleeping".

The problem and solution it turns out was very simple:

I ran Memtest86 and discovered several random memory failures. I started removing memory modules to diagnose where the problem was. It turned out that the guy who installed my extra 2x8GB memory had not paired these modules and the original Apple 4GB memory modules correctly (with 2 similar DIMMs paired in each of the 2-slot memory banks). Once I swapped the DIMMs to a correct configuration / pairing, I got a clean bill of health in Memtest86 and the OS x 10.11.4 random crashes have now been gone for more than a week.

So it seems that OS X 10.11.4 might have installed a firmware update that somehow makes the iMac more sensitive to incorrect / incompatible memory configurations and perhaps also to slightly faulty memory (or even memory modules sitting loose in their slots). So I would suggest everyone experiencing these problems to try the following:

A) Ensure that memory is paired correctly with 2 identical modules in each bank (i.e. slot 1&2 and slot 3&4 each need to be fitted with identical modules)

B) Ensure that all memory modules are fully pressed into their slots and not sitting loose

C) Run Memtest86 (http://www.memtest86.com/) to detect any faulty DIMMs (perhaps the upgraded firmware has changed something about the voltage / the physical interface to memory, pushing some types of memory / memory configurations to behave in a faulty way).

It is at least worth a try. Good luck!

PS: The machine was rock solid with the incorrectly paired memory for more than a year and the problems only started when I installed OS X 10.11.4.

Thanks for the tip, MMartiny! Yesterday I ran Memtest86—beware: the testrun clocked 9,5 hrs.—and no errors or memory failures at all showed up.

One of these days I'll inspect the physical memory slots too. The past ten days or so, random restarts seem to have stopped without me having done anything beyond day to day ordinary work on my iMac.

Posting and troubleshooting from the Netherlands. I've been trying to resolve this issue for a customer of mine for some days now. As added information I performed the following troubleshooting efforts:

- Disk Utility check from rescue partition

- Boot in single user mode and check permissions

- Boot in single user and file system check disk (fsck -fy)

- EtreCheck (to check for warnings and anomalies)

- Check Acitivity Monitor and Console for irregular performance or logged issues/crashes.

- Deleted old User settings files and general files

- Deleted Apple Mail 'Containers'

- Deleted com.apple.xbs

- Deleted .isdata files (icons cache)

- Updated Adobe Flash Player plug-ins. (PPapi and NPapi components, known issue with Safari)

- Tried the iMac 5K without Spotify (there was a known bug)

- Deleted and re-indexed Spotlight index as there was a lot of mdworker processes going on in Activity Monitor

- Applied Apple 10.11.4 Combo update

History: iMac 5K (december 2015) with 32GB RAM (2 x 8 + 2 x 8). I had a real hard time finding the correct timing RAM modules (DDR3 1867MHZ PC3-14900) only to find to my dismay Apple used 1600MHz themselves! System profile also shows 1600MHz (as PC's and Mac's tend to opt for slowest common RAM denominator)

Next up is removing my RAM modules in order to rule this out.

iMac 5K was running fine without crashes, but started behaving erratically after 10.11.4 update and now crashes at least 3 to 5 times a day with a beachball and an eventual reboot without error codes onscreen.

I have not had restarts that frequently, but I was still getting them. Most of the time they occur during sleep or waking from sleep. I tried the Memtest mentioned above posts, but it yielded no errors. I spoke with an Apple engineer last night. They do review these forums and were investigating the possibility that this was a bluetooth related issue. He had me upload a bluetooth diagnostic report done in terminal.

This morning, 10.11.5 was released, so I updated. No restarts yet. If I get any more restarts, I will turn off bluetooth and switch to a wired keyboard and mouse to see if the restarts continue. Hopefully the update has addressed the issue.

Not one restart since installing 10.11.5 yesterday, mine was getting worse with one or two restarts each day/night. My restarts would only happen in standby never when awake and in use. Hopefully it's been fully fixed in this release.