I've resolved my issue by replacing the LED BackLight board (cost me about 45 EUR via AliExpress). Got it fixed within hour by following iFixIt tutorial. Was quite easy to do, just take your time. If i need to do it again i could do it within 15 minutes... :-) Display hasn't failed once since i replaced it!
I bought an used iMac with this problem for a good price to solve the problem, just like you. I got it temporary worked around, maybe you can try it. Unplugging the power for a while and putting display brightness to lowest seem to have worked around the problem for a while. I think the built in power adapter or backlight board is the issue. These are both always powered when plugged in. This week this workaround didn't work anymore and I'll replace both. I'll let you know what the culprit was. If you have it resolved before me please let me know what you did. Dennis van der Pool
I bought an iMac with this problem for a good price to solve the problem. I got it temporary worked around, maybe you can try it. Unplugging the power for a while and putting display brightness to lowest seem to have worked around the problem for a while. I think the built in power adapter or backlight board is the issue. These are both always powered when plugged in. This week this workaround didn't work anymore and I'll replace both. I'll let you know what the culprit was. Dennis van der Pool
