Level 3

778 points

2017 iMac keeps suddenly shutting down

Today my 2017 iMac has started suddenly shutting down, as if the power has been cut (it hasn’t). After it’s shut down, I can’t turn it back on unless I also turn off and restart the attached power bar. This has happened around ten times and counting.

Assorted points:

There’s no warning or anything. Just the faintest of flashing sounds and the screen goes black. Indicator lights in attached external hard drives also turn off.
After a crash, if I press or hold the power button on the iMac, nothing happens. If I turn the power bar on and off, I’m able to restart the computer immediately. I don’t know if I’d be able to eventually restart the computer without switching the power bar on and off; perhaps I just haven’t waited long enough.
I’ve tried changing the specific plug (but same wall socket) - still shuts down.
I’ve tried a different power bar - still shuts down.
I booted in Safe Mode - still shuts down. (Twice I tried rebooting in Safe Mode and gave up after waiting 30+ minutes; then I restarted in normal mode, that worked, and restarted in Safe Mode from that. But it crashed in Safe Mode pretty quickly.)
I haven’t yet been able to keep it working long enough for Etre Check to run.
When it crashes, it always seems to be the instant I do something: select a different app, run a command. I don’t think it’s been triggered from just typing in an app. I haven’t found any consistency with which action “triggers” the crash (if indeed that’s what’s happening, rather than just a coincidence.) I’ll do a bunch of stuff without issue, and then the next action will crash it.
Since the problem started this morning, the longest I’ve been able to use the computer without it crashing is about 30 minutes (and often more like two minutes), but it successfully stayed on for a couple of hours while I was out for a walk, and it did at least two Time Machine backups at that time. Right now I’m letting the iMac run a SuperDuper clone, and I’ll see how far it gets.
I can’t find any crash reports. In Console, when I look at system.log, there doesn’t seem to be any indication of a problem - just running normally. I can only find the point where it crashed by looking for “BOOT_TIME” in the log.

Beyond my general request for help, is there anything I’m missing in Console to give a better log of what’s happening? In the past I’ve had things like “You restarted your Mac because of a problem,” but this time there’s nothing - when I turn the system back on, it reopens all the old windows, with no indication at all that anything untoward has happened. And then it’ll crash again.

iMac, macOS Mojave (10.14.1), 2017 iMac

Posted on Dec 1, 2018 12:42 AM

24 replies

etresoft

Level 9

56,308 points

Dec 17, 2018 10:37 AM in response to Lost in Asia

1. OK, I'll try that. Just to confirm before I embark on this process: I assume I need to ...

Back up everything (I've got two Time Machine drives going, plus SuperDuper clones I normally do every three days).

Generally you very rarely hear anyone say “****! I wish I hadn’t backed up my computer!”

Wipe the system, reinstall new OS: I plan to follow the iMore steps1. for wiping the system.

Not so fast. You have to restore your machine at a very low level. To restore your Fusion drive, you will have to follow these instructions: https://www.techrepublic.com/article/pro-tip-how-to-create-and-disable-a-fusion-drive/

This will require booting from a High Sierra boot drive and reinstalling High Sierra. Mojave won’t work for a number of complicated reasons.

See if the SSD is functioning on the "new" system. How should I test this?1. I can go into About this Mac / Storage, and see if it's 2TB or more than 2TB. Or: right now, when I look in About this Mac / System Report / Storage, and look at my Macintosh HD, I see only the HDD listed - there's no entry for the SSD. Should there be one? Are there other useful ways to see if the SSD is working?

If you are able to restore the Fusion drive and reinstall High Sierra, then that is as good as you’ll get.

Gulp. Last time I restored from a backup, just three months ago, it took days for the system to reinstall everything, and then maybe a week for iCloud to sort itself out.

I wouldn’t worry too much about that. I’m quite confident you’ll never get that far. I wrote my last reply while traveling. Now that I’m not as tired, it is pretty clear that you need to take your machine to Apple right away. Don’t bother with any of what I wrote above.

For my curiosity about when this got scrambled: remember this thread started because of a sudden shutdown issue (which, oddly, hasn't happened in a couple of days). I still wonder if the sudden shutdowns and the detached SSD are related or completely distinct issues.

Sure looks related to me.

(I'm curious how common a problem this detached SSD is. I haven't been able to find any other instances, but perhaps my Google skills are lacking; however, there are very few unique problems.

I’ve seen a number of them just in the past couple of days. I think it is a combination of Apple’s Mojave which just happens to be the most complex operating system every made by any company, compounded by people trying to do low-level command line hacks on the operating system.

Lost in Asia Author

Level 3

778 points

Dec 18, 2018 5:16 AM in response to etresoft

They don’t seem to provide on-site service here in Taiwan. I asked at the small and nearby on-campus retailer where I bought the machine: they can move the computer on to a service center for me, but it’ll be sent out somewhere else, and will come back in one or two weeks. Or I can carry it across the city to the single Apple Store and try to get things sorted out there, with apparently a typical 2-3 day turnaround time. I prefer the latter because if the computer is being shipped back and forth at one-two week individuals I can envision several repeats of “No, you didn’t fix the problem”, whereas at least at a Genius Bar I can turn the machine on and show them what the issues are.

I’m glad I kept the box - that makes carrying the machine easier.

Nope, no Apple Care - roughly four weeks left on the warranty.

The most frustrating part of the whole thing is I’d originally intended to buy a 500GB SSD, but reluctantly opted for the larger Fusion Drive because, at the time I bought the machine, it seemed that Apple didn’t let you use Time Machine to back up a Photos Library stored on an external drive. And about a week after I bought the Fusion Drive, the information changed, and externally stored Photos Libraries were declared fine for Time Machine.

Lost in Asia Author

Level 3

778 points

Dec 24, 2018 3:13 AM in response to Lost in Asia

Progress report: last week in the Apple Store the third Genius I worked with managed to get the Fusion Drive, well, fused again - I was seeing the 2.12TB storage, for example. Yay! And they kept it in the shop for tests re: the sudden shutdowns. They called me a couple of days ago and said I could pick it up; I went in, and they explained they’d had the machine running at a high CPU rate for a while (I think?), and hadn’t had any shutdowns. I pointed out that the shutdowns had had nothing to do with high CPU load, and had often happened when I just had one app opened, and was simply in the middle of typing: the system shut down upon me inputting something, and wasn’t correlated with how much work the machine was doing.

I persuaded them to do more testing with it, and they should call me in a few days. Surely there must be some kind of record in the logs they can look at, even if I don’t know what to look for. I kept suggesting they check the power supply, even though I’m not 100% sure that’s even a thing, and I’m sure they’re sick to death of people like me who have read a few threads on the internet and therefore consider themselves experts.

Dunno if I’m being a jerk with it, but taking the computer back and forth is VERY annoying and I really don’t want to have to do it again, especially since there’s only one Apple Store in this city and it’s very busy and as far as I can tell it’s impossible to make an appointment. As in, every time I check, there are no appointments available over the next eight days, and they won’t let you look further ahead than that. At least this time they let me leave the empty box in the store, rather than trucking it back across the city yet again.

etresoft

Level 9

56,308 points

Dec 24, 2018 5:39 AM in response to Lost in Asia

It sounds pretty good so far. Any logs from your old configuration are not going to be useful. That broken configuration itself is reason enough for the crashes. A high CPU load is a more typical cause for such a problem so they are taking a logical approach. There is no guarantee that they will be able to reproduce the crash. There is still the question of how your machine got into this configuration. If there was some kind of hardware fault, then you may still have trouble in the future.

Dec 30, 2018 3:16 PM in response to Lost in Asia

I have the same issue, I wiped out the whole system and reinstalled everything and they did all their tests several times, but it still happens without any specific pattern!

https://discussions.apple.com/thread/8586415

etresoft

Level 9

56,308 points

Dec 30, 2018 5:06 PM in response to Lost in Asia

I’m still confused why there’s no way to look at the system logs and see “Oh hey the computer shut down because of a sudden loss of power these multiple times”, but this certainly isn’t the first time that computer diagnostics have confused me, and it won’t be the last.

The diagnostics aren’t that good. There is a value for “last shutdown cause” but it is only for the last shutdown. Unless there is an actual panic, there is no direct record of these kinds of shutdown. There may be some evidence in the logs, but the logs are a mess and not worth anyone’s time to try to read. To be honest, with your system in that state, no amount of diagnostics would be worth the effort. When there is something so obviously wrong, any diagnostics collected at that time have no value.

You are doing as good as you can.

etresoft

Level 9

56,308 points

Feb 1, 2019 8:19 AM in response to Lost in Asia

Thank you for the follow-up!

ajcooke01

Level 2

311 points

Dec 1, 2018 4:52 PM in response to Lost in Asia

I have a hunch that your iMacs power supply is going bad. Too bad I can't give you instructions on how to test for a bad power supply though. Make an appointment and take your iMac into an Apple Store to be looked at. Don't let the "geiniuses" overcharge you though. Use common sense and when they tell you what they are going to replace think about if it makes logical sense that this could be the problem.

Contact Apple Support

Lost in Asia Author

Level 3

778 points

Dec 19, 2018 2:07 AM in response to Lost in Asia

Question: is there anything I can show the Genius Bar, on my computer, to demonstrate that the Fusion Drive isn’t working properly? They keep looking at me like I’m sort of mad, when I’m pointing out that my computer has total Storage of 2 TB, and the sample iMac at the next desk over has total storage of 2.12 TB. (I’m also running into a Chinese/English language barrier here.)

EDIT: OK, I’m also looking in Disk Utility, and I see that my IMac has two separate internal hard drive, HDD & SSD: and their iMacs have one drive, just called Macintosh HD.

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2017 iMac keeps suddenly shutting down