iMac 27" 5K Late 2015 screen artefacts on shutdown

I just got a replacement for my iMac 27" 5k late 2015 with Sierra OS and after 2 days am starting to have this problem again. I am new at this and have no clue as to why. The computer works ok otherwise. Back to the PC world?

I have the exact same problem. It showed up when I first got the iMac (iMac retina 5k late 2015 model, 3.2GHz Intel Core i5, AMD Radeon M380, 1tb Fusion Drive) which scared me because that's what killed my old iMac. Stopped for a few months and is showing up again. Wonder if there's anything to do with the USB port...Because the blue lines came back after I attached an external HD for my time machine.

My old iMac died after the screen did the same thing. It's very scary seeing those lines. Anyone has any updates on it?

Thought I'd give OS Sierra a go again today as El Capitan had been giving me a bunch of issues of late (randomly freezing and crashing). The problem reappeared instantly in a completely fresh/clean install of OS Sierra. No external monitors connected or anything.

A few-month-old Mac (Retina 5K, 27-inch, Late 2015). Sierra 10.12.3.

I already returned my iMac once, when first purchased, due to this issue. The new (current) iMac has had the same problem. Waiting for fix like everyone else. I'm going to live with the issue for now, I guess. I'm done with downgrading back to El Capitan.

I have and after a bunch of hoop jumping Apple replaced my iMac because it was still under service and they could not fix the issue. From what I have seen it is a problem with these 2015 iMacs. This new one has had the issue once but it was restricted to the lower right of the screen not like the old one that had the entire screen full of the horizontal blue and green lines. No one I know can figure out why this happens. For me it was once in a while but my old iMac also had other issues.

It never occurred under El Capitan, only Sierra, so I would think its not the iMac as this would be a much bigger issue, its a driver/kext issue I would imagine introduced with Sierra. Also I think some people are mixing up the shut down issue with actual hardware problems by the looks of some of the posts.

I'm seeing it intermittently (cyan/magenta scramble on the screen) on shutdown, but in the following sequence: (1) screen goes dark (not black), indicating that it is still getting power, (2) the scramble, (3) screen goes back to dark, (4) after another second or so, the screen goes completely black, indicating that it is no longer getting power. Don't know if this helps anyone figure out the problem, but the glitching seems to happen well before the computer finally shuts down.

Here's hoping Apple comes up with a software or firmware fix for the problem.

I sent the fourth iMac 27 "late 2015 and this the 20 early days I worked well.

And now back to appear the stripes to the turn off it.

Is frustrating as have past the days of a return u now it would have that repair.

I don't think I do that four iMacs this defective must be otherwise.

What occurs that does not enjoy of my iMac why am pending of that leave them lines blue magenta etc in the screen.

:-(

I've sent my iMac to the service center 4 times (it's an iMac Retina 5k, 27inch,late 2015). It still have the multi colored artefacts during shutdown after collecting it from the service center for the 3rd time. The 4th time i went there, I told the service center to do a downgrade to El Capitan since I suspect it might be the OS issue and the service center did a full MRI and nothing is wrong with the hardware. In less than a day since i did the downgrade my whole iMac hang while i was working on Adobe CC Illustrator. Now every time i turn on my iMac and log in, it will hang at the desktop and then restart.

I've called AppleCare requesting for a refund. As this issue has really stressed me out since last year October, and my work production has been delayed (I had to make a total of 16 trips to the service center and it's really far away from where I live. Carrying a 27inch iMac is no joke, it's really heavy).

Took Apple about a week to get my reply on the refund and their answer was to simply replace my iMac and if it's defected they will repair it. That's it. Seriously...how is this any different from what i already went through?? I'm really angry and frustrated as an Apple customer this is really a HUGE disappointment. Tomorrow they will be calling me back again to get my answer on whether or not they will be replacing my iMac with a "brand new one". It's not like I have a choice in this issue.

Replacement with the same thing seems to be how Apple operated having a similar issue and "resolution". None of the diagnostic tools find any issues yet the problem persists. I have been watching this forum for some time and it appears that we are not alone in dealing with this issue and while it took Apple over a year to replace my computer the replacement has some of the same issues just not as often. Because Apple can't or won't fix the issue it would appear that while they have my money for this computer the words "return to PC's" comes to mind as I surely don't want to spend more of my hard earned money on a system or company that doesn't stand behind a defective product. I say defective product as my son has several older Apple products and none of them has the issues this one has. Good luck, I thing a lot of us could use some.

I wish I had read all these posts before buying / returning 3 iMacs during the last month. I've tried 2 different models (M390 and M395 GPUs) and BOTH of them have this shut down issue.

It's weird that Apple Store employees were not aware of this issue...

Why this has not been addressed seem to be a priority issue with bugs...seems to me that one of these betas should have done it. Worried this is more than software now that most of my units are out of warranty.

I'd just like to add that I have been following this thread and have the exact same problem all of you have. My lines upon shut down were very random for the last month or two, but now seem to occur each time I shut down.

I have the exact same issue, it some times wont do it for a few weeks then suddenly it will do it every time I shut down or shutdown and reboot. It doesn't matter how many times I speak to Apple, they look into it and I don't hear anything back from them even if I send them an email to the person who I have spoken to they never return my emails, Apple customer care is crap - I doubt I will ever get another one of their computers again! It took them nearly a year to get my iMac booked in to get repaired, as soon as I purchased it it used to just reboot without warning and the fans would spin up, I kept telling them it was a hardware issue, in the end I lost my temper with them and they finally got it in for repair - turned out the logic board was faulty they replaced it and it has not done it since. Then this issue with the coloured lines on the screen, I wanted them to replace it but they wouldn't they said they will try and fix the problem but they still have done nothing to rectify it, I can't even find anywhere where I can make a formal complaint about the way I have been treated, so this is the next best thing I can do.

My last iMac was a mid 2011 21.5" model and I had no problems with that at all so this is why I decided to buy another, I wish I never bothered. - Apple don't seem to care that their customers are unhappy they have our money thats all that they care about.

anyway rant over - for now!

I thought I'd give Apple support another call. Each time I call in I get a different response.

A few weeks ago, when I first called support for THIS iMac (returned the previous one for same issue), they gave me the vague answer that there would probably a fix in an upcoming version of Sierra. This past week, a different support rep told me that this was something they'd never heard of before, and forwarded my information to the Apple Engineers. Note** She suggested that going through support would be the ONLY way they would catch wind of the problem, so I hope everyone here has tried to go that far.

She then told me to book an appointment with the Geniuses--but after reading this forum, I see no point in playing with random hardware replacements. I already replaced this iMac once, and the problem only appears the moment I upgrade to Sierra.

I made the decision to extend Applecare in case this does prove to be hardware (probably their plan all along). I really hope they figure something out in the next two years. That should be ample time, no? Considering the high-end Windows rig I could have for what I paid on this iMac, I'm really starting to question my decision on choosing Apple.

P.S. I've found a novel solution in the meantime: Don't turn off the iMac.

According to Apple Support, it uses more power to turn it on and shutdown each day. The few times I've left it running for a week, I also haven't had the glitch on shutdown.