Thin Red Line
Why is there a thin red vertical line on my 2017 iMac display across all platforms. It's annoying and as the warranty just ran out Mac wants $800 bucks to fix???
iMac 21.5″ 4K, 12.2
Question marked as
Keeping in mind that we are just users like you and may not be able to pinpoint the cause.
I’m going to suggest that you attach an external display and see if it shows the red line. If it does show the line it would suggest a problem with the video chip. If the red line doesn’t appear on the external display it would suggest a problem with the built-in display panel.
A couple of basic things to try are to reset the SMC 3 or 4 times in a row and/or see what happens in Safe Mode.
