Chosen Solution
My iMac’s display functions normal through boot up but then goes black anywhere from 10 seconds up to a minute or so after fully loaded. It works perfectly fine on a external display. Often when I leave my computer to sleep and come back to it, it will once again come back on for a short amount of time. This started gradually probably 6 months ago. It would go black after using it for an hour or so and over time would go black quicker and quicker. I brought it to Apple and they determined it was a backlit issue, which they replaced. It worked for maybe a week before it started happening again. Any help would be very, very appreciated! Thank you for your time in advance.
As long as can see the screen, the GPU is good and so it the LCD. Replace the driver board: iMac Intel 27" EMC 2309 and 2374 LED Driver Board Replacement
