2017 iMac Issues with External Displays

[Sneakz]

10.14 is causing issues with my 2017 iMac (iMac 18,3) with a Radeon 570. When outputting to a older Samsung Plasma TV using a USB-C to HDMI adaptor, the display is clearly discolored with a purple hue. The same setup works just fine under 10.13.6 and using the adaptor with my 2016 MBP with a Radeon 460 works just fine in 10.13 or 10.14. So I'm certain the iMac is the problem or in particular, 10.14 AMD drivers for the GPU. Is anyone else experiencing an issues like this?

 

[SCMedic]

At least yours is working. My 2017 iMac won't even send a display signal to my Dell Ultrawide. Started with latest Mojave install.

 

[Sneakz]

I also have a LG 31MU97 connected at it works just fine at 4096x2160. But the TV issue is puzzling.