Chosen Solution
My screen just flickers and doesn’t change after shutdown and restart. The external screen is operating as it should. Is this possibly a cable coming loose or logic board replacement? I appreciate any assistance of resolution. Update (08/18/2021)
Let me know if this is not viewable?
@Kwin - Sorry I lost track of your problem ;-{ Sadly it does look like your T-CON board on the back side of the display assembly has failed. If you remember back in the day when we had CRT based TV’s if you messed with the horizontal setting you would see the image of the display roll like yours, once you play the video slowly! This is the same problem you are facing as the horizontal lock is not working! Time for a new display assembly: 27” iMac Display Assembly, Apple P/N 661-7169 and here’s the guide to put it in iMac Intel 27" EMC 2639 Display Replacement Make sure you get the full kit iMac Intel 27" (2012-2019) Adhesive Strips so you get the needed tool and I would get a second set of tapes just in case! Lastly, you’ll want a pile of these (4 will do) Plastic Cards
