A quarter section of screen of LG LED 60LS5750 is faded gray-no black

A quarter section of screen of LG LED 60LS5750 is faded gray-no black

TV still works, but exactly one quarter of screen is faded. When display is light (daylight scene) it is hardly noticeable, but scenes with darker colors show whole left quarter section of screen several shades lighter. I checked connections and switched over T-CON cables, but no difference. Any ideas? Thx.

ANSWERS: