iMac keeps going off

[cazthebabe]

My iMac keeps going off like the plug has been pulled. Not sure if it was after the 10.11.5 update or not, but it does not re-boot automatically. I have to disconnect power cable then go through the SMC routine and sometimes it reboots. I have run an Apple diagnostic which has turned up no errors or faults.

It is driving me nuts! Anyone any ideas?

Some details:
27" iMac
El Capitan 10.11.5

Thanks

 

[MCAsan]

Got the latest firmware? https://support.apple.com/en-us/HT201518

Did you try resetting the Mac's PRAM, SMC, and NVRAM?

 

[cazthebabe]

Yes, tried resetting.Still doing the same.

 

[MCAsan]

Maybe time for a full OS reinstall. Of course only after making sure you have incremental backups such as from TM.

 

[cazthebabe]

Hi, yes done that with 12 minutes left on the install it just went off again. Finally got it on again and finished reinstalling booted up as normal to virgin desktop and 5 minutes later it went again. Would not reboot without SMC. It switches off like the power has gone.

 

[MCAsan]

Could indeed be a problem in the power supply. Definitely time for a trip to Apple Store or other authorized repair center.

 

[JohnDS]

What do the system logs say immediately before the shutdown? Your symptoms sound like overheating.

 

[cazthebabe]

Hi, ended up taking it to Apple Genius and apparently it is the LCD display and they are going to replace it under Consumer Law. Thought I would let you know as you have been so helpful.

 

[MCAsan]

Sorry you had the problem but very glad Apple is taking care of it!