Q: 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