Chosen Solution
So the other day my iMac 5K 2015 died when I accidentally flipped a power switch on a power strip during an update from OS X 10.14.5 to 10.14.6. Now all that happens when I turn it on is that the fan goes on (pretty lightly) and off with a 3 second interval. Nothing more. Black screen. I’ve now turned it in to a repair guy but he hasn’t found the fault yet. Things that have been tried: All types of resets (SMC, NVRAM) and short commandsLeaving it off without the power cord plugged in for 24 hoursRemoving all RAM and starting (then it beeps and the fan goes on)Trying the RAMs separately one by one in the top slotReplacing the power supply ..and some more. Does anyone know what the issue might be?
Sorry to say you mangled your systems firmware. Killing the power in the middle of an OS update can kill your logic boards EEROM chip’s programing (EFI firmware). Well you are between a rock and a hard place here! You’ll need to visit an Apple Store for them to Gulp! replace the logic board. Apple won’t reprogram the firmware only replace the part. The newer Thin Series iMac firmware is very different than the older 2011 and older models. I tried once to do it and only made a mess!
Did Apple warn you that their update had the possibility of killing your machine? I don’t think so. I’d take it to Apple and tell them the update killed it and have them repair it gratis. I would not mention the power interruption.
