Chosen Solution
My iMac started to show strange horizontal bars (perfectly dividing the screen into 4 areas), with flickering lines. The colors of these bars are blue/black. Adjusting the brightness cause the bars get less or more visible. Replaced my HDD with an SSD 6 months ago without issues until now. I was reading about opening the iMac and damaging the LCD display connectors. The display works perfectly when it’s connected to an external monitor, wired or via airplay. Did any kind of tests, even Apple Service Diagnostics, no issues found.
Thanks in advance
What does an external display look like? If its clean then the display assembly is damaged, it the external show the same markings then the logic board has problems.
Since you can connect to an external monitor IMHO I think you are correct. It sounds like the LCD display connectors have been damaged. I’ve never repaired/replaced that but perhaps the iFixIt archives will have something? Good luck.
I seem to have the same issue. iMac screen is messed up but “clears up” after some time. Hooked up to external monitor no problem. Brought my machine to Apple and they couldn’t 100 Percent give an answer. Computer is in working order except for the mysterious screen issue that comes and goes. Nobody knows what to do.
