Help with 2017 iMac random shut downs

[mollyc]

I am having difficulty with my 2017 iMac and random shut downs. Actually it isn't even shutting down, it just goes completely off.

I noticed it once about a week or so ago when I had left it alone for a few hours. I came back and it was seemingly off. I tried holding the power button to get it to restart, but I was only able to restart it after unplugging it and plugging it back in. I thought at the time it was a one-off glitch.

Yesterday I was using it for about an hour and it went black with no warning. Again, the only way to restart was to unplug the machine from the wall. I have tried the following things:

• unplug all peripherals
• boot in diagnostic mode (no errors found)
• reset pram/nvram (no change)
• boot in safe mode. This got me about 8 minutes yesterday of on time, then it happened again. subsequent safe boot would crash immediately upon getting to the home screen.

I finally gave up yesterday and left it unplugged all night. I now have it on and was able to copy some critical files to my MBA. The other thing I did just now was to unplug the ethernet cable which I had not done yesterday. At present it has been on for about 15 minutes with no issue, but I honestly think it will turn itself off again within the hour.

What other trouble shooting things can I try? I am loathe to try to update it for fear it crashes in the middle of an update and my hard drive gets ruined. My husband is willing to replace the power supply if we think that is the culprit; I am out of warranty and he has opened previous iMacs and can build a PC, so I am not concerned about the swapping, more just if it is likely that is the issue.

These are the specs of my machine:

• 2017 iMac, 5k 27"
• 4.2 GHz i7
• 40MB 2400 MMz DDR4 (32GB is after market, the original Apple 8GB still installed--I have not taken out the additional RAM yet)
• Radeon Pr 580 8GB
• 1TB SSD drive
• Mojave 10.14.6

I would appreciate any help or suggestions someone might have. The shutdowns happen regardless what program I am using, so I don't think it is inherently software related, other than perhaps needing an update of some sort.

 

[TwoH]

Have you tried taking out the after market ram and seeing if it lasts any longer ?

edit: sorry just seen you said you haven’t - this would be my first culprit for random shutdowns.

 

[mollyc]

Have you tried taking out the after market ram and seeing if it lasts any longer ?

edit: sorry just seen you said you haven’t - this would be my first culprit for random shutdowns.

Thank you, I might try that.

Actually though I have been doing some more work on it and I have a strong suscipicion now that the culprit is actually my NAS. I discovered that one of the drives has crashed and I think when my iMac was trying to mount it that was causing the shutdowns.

I mounted the crashed drive through my MBA and was able to back it up, but since having it unmounted from my iMac I have not had any issues. I noticed in the NAS software that it recorded the first crash seven days ago, which correlates to when I think I had the first random shutdown.

 

[vitale]

My 2017 4K iMac was doing the same thing for about a week back in January. At some point it resolved itself, so I think it may have been software-related. It's been running for over three months now without incident (I left it unplugged for a few weeks), so not really a 'great' solution I can offer, just know that it's not just you.

 

[Fishrrman]

"Actually it isn't even shutting down, it just goes completely off."

Completely black?
No fans, no nothing?

Sounds like the power supply, or perhaps a loose connection thereto.
Have you tried re-seating the power cord at BOTH ends?

 

[mollyc]

"Actually it isn't even shutting down, it just goes completely off."

Completely black?
No fans, no nothing?

Sounds like the power supply, or perhaps a loose connection thereto.
Have you tried re-seating the power cord at BOTH ends?

Yes I did try that. and yes it went from on to immediate black screen. Solid off black, not even the matte powering up black.

But since I have unmounted the NAS with the corrupted drive I have had no issues. I think there was a weird glitch when trying to mount it while showing as crashed.

I am going to replace the nas drive (which obviously needs to happen) and see if that changes things. In the meantime I am just not mounting the nas.

 

[mrBirdie]

So, did anyone get this resolved? My 2017 iMac with 580 pro has randomly died like 10 times, last 2 weeks. Completely random. Sometimes 1 hours after startup, sometimes 6 hours, sometimes 1 minute.

Tried swapping around/removing ram.
Tried booting windows from external drive.
Checked temperatures.
Tried UPS and switching power outlets

I let the apple 'experts' look at it. They had it on for 8 hours, and said it was no hardware-related errors. Recommendation from Apple: Try re-installing Mac OS. Even though I made it clear that I already booted windows from external drive and had there same problem. I don't know if they employ these people directly from the sewers. ****ing rats.

There aren't any logs. I've checked. Is there any way to know where the fault lies?

Its either the PSU or the Logic board - and I don't want to replace both if its unnessecary.

 

[mollyc]

I am the OP. My husband replaced the power supply for me in July and I haven't had any issues with it since. ? He got a kit on ifixit with the requisite PSU.

 

[mrBirdie]

Thank you for the quick reply.

So frustrating. I will do the same and hope for the best.

 

[vitale]

It's definitely the PSU!