Chosen Solution
I have seen a lot of posts regarding the stage light effect on the MacBooks, but I have a 27 inch iMac that had the same issue for about 2 weeks. It was sporadic, as sometimes it would be there and others not. Today the screen is totally black. Is the stage light effect indicitive of what the cause of the display going black might be?
The stage-light effect is caused by either the LED driver failing or the cable connection to the display assembly. Rarely is it the display its self in the iMac’s. The only time I’ve seen a bad display is when someone damage it. The more common issue is the LED driver logic is failing and as you’ve lost the backlight fully now that’s what I focus in on. Update (09/07/2019) Here’s the needed part Backlight LED driver board Apple P/N 661-5980 iMac Intel 27" EMC 2429 LED Driver Board Replacement
