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

Emptynet, how did the power supply replacement work out for you? I found a YouTube link where someone was posting that a Logic Board replacement AND a power supply replacement has fixed his issue. (https://www.youtube.com/watch?v=ka7lUIeiH5E) I'm hoping it will fix mine also.

I've tried some other workarounds I've found from other issues (turn off bluetooth - bought $29 wired keyboard&mouse, turned off Safari Web GL) but even after the Logic Board replacement this is still occurring for me. Backing up everything at the moment and handing in my iMac until they fix it again. Hopefully it'll come up with something. It's been almost 6 months now.

Hi Dyslexicant. After the Geniuses replaced the PSU they *then* saw evidence of issues with the graphics part of the MLB, so that got replaced too. However, during the repeated assembly / disassembly the hard drive connector was damaged, so that *also* got replaced. I finally got the machine back in my hands yesterday, so I've not had time to know if it's completely sane yet. I will monitor for the next month or so and either post an all clear or any further weirdness. I have 90 days warranty on the current crop of replacements.]

Cheers, Mike

So I dropped my Imac on August 30 and explain my situation. He ran a program to check if there was a hardware issue. The results showed no damage to the hardware and wanted me to leave the Imac for more testing. After 2 days I got an email to pick up my Imac, I was excited but also confused because the email said they will call me 3-5 days. Only 2 days of testing is not enough thats what I told them when I got to the apple store. They said they could not replicate my problem and there was no hardware issue. I was very frustrated and in a rush so I told them I want to leave it longer in the store for more testing.

After 2 days I got an email saying they have some information for my device. I called the store and they said the same thing. They said there are no signs of hardware issue and could not replicate the random freezing and restarts after leaving the computer on many hours stress testing it. I gave them one more day for testing and decided to call the following day in case they failed to call me. I called september 4 that was a sunday, they told me they were able to repeat my problem. They said its not a hardware problem but a software problem that affects certain Imacs or mac.

They told me I need to wait for apple to update their firmware. Seriously this started happening since updating my system to 10.11.4 and so on. My problem began since march to September, that's a lot of months of random freezes and restarts. So I have my Imac back but the problems are still occurring. Its really making me angry and frustrated when the problem occurs.

I feel your pain.

Mine has been taken in twice to no avail also stating they could not replicate the fault.

It was then picked up and the logic board replaced , they said this had fixed it and sent it back to me, I had it on for 25mins and it was restarting, it had also come back with a different serial number??? So I called them the same day and it was collected the following day. It's now been there 5 weeks. I called them on the second week for an update, they stated they were going to again replace the logic board with regard to the serial number issue but as far as the restarting they had no idea.

I heard from them yesterday after a frustrated email, I bought this imac brand spanking new for work and uni going on 7months ago and haven't had a solid days use out if it, biggest waste of £2000 , and they just don't give a crap.

They have apparently isolated the problem to the ram , so it has been ordered and I'm now waiting for this.

I'll believe it when I see it

Cheers to paying full price for faulty items

Over the last 5 days I've tried a few things ( in the effort of making a new TM backup so I can send mine in for repairs again) and I've noticed something...

First of all, I'm trying to get a new Time Machine backup which (after removing and backing up stuff elsewhere to save time - and the fact I ran out of space on external hard drives) has so far taken 4 days to backup 600GB out of 1.6TB, my iMac has not crashed once.

I've had it dimmed overnight and during the day when asleep, kept a video playing on repeat, to not allow it to sleep or anything, but most importantly I bought a wired mouse and keyboard and turned Bluetooth OFF. So far, 4 days straight whilst backing up and no issues.

Prior to this, opening up files with Preview killed it instantly. This was a bug from 10.11.3 so I've read.

I am not game to touch safari or anything else until my TM backup is done, I've got no TM backup currently (it's doing its initial one again). So I'll let you all know what happens once the TM backup is done. Some people did mention Bluetooth being an issue with responsiveness etc. maybe it's something, maybe nothing, but I'll see how things go.

I did have troubles with bluetooth off and it did crash but I believe that was due to the Preview thing, but so far there's no issue in 5 days.

It seems not to isolate to 5k Macs with 10.11.5. My iMac Late 2013, Mavericks, began these days too with Random Restarts, preferably at night.

Same for my late 2015 imac (Fusiondrive and M390).

In my case it seems that it is since RAM change (Corsair, Apple certified, 32GB), I'll now insert original 8GB and check if it happens again.

BUT it seems from other users that RAM is NOT the issue, most likely the logic board...

I can throw a spanner into the works. 2 logic board changes did nothing to mine., I got it back two days ago after they said theyhave just swapped one of the ram cards that was faulty. It seems pretty stable at the moment....??

Yes, my reboots are all at night.

And i have no standby activated, only screen and HDD powerdown.

I found that taking the o/s back to 11.10.4 completely solved the problem.

But Apple in its infinite wisdom, insists on upgrading me to 11.10.6. So far I'm saying heck no. Any way to get the script to stop suggesting the upgrade?

Thanks!

btw it is NOT the RAM 😉

Anyone tried latest Sierra build (GM)?

I've upgraded to Sierra GM last night. No issues so far, but then again I had been using EC for the last week and not touching it whilst it did a TM backup. I'll let you know how things go (mine was the black power out issue - not he restarting problem like others).

Thx! Reboot today at 2pm (not in the night anymore...)

I'll backup now and also upgrade to Sierra this evening (GMT)

I speak too soon. Happened again last night, on Sierra GM.

Usually it would happen repeatedly after I turn it back on, but this time it didn't. It was fine afterwards and I had it on for a little while longer with no issues. I am wondering if it is a power issue.