iMac display/lcd has a horizontal lines colored according to the color displayed by the screen
my iMac 21.5 inch late 2009 ati radeon 4670 screen has a horizontal lines after update to macOS el capitan from snow leopard. and now has shadow on the screen after update to High Sierra. Btw, the flat line is colored according to the color displayed by the screen. Is the gpu or led problem? when i take a screenshot the picture is normal. how to fix that?
This the preview.
iMac, macOS 10.13