If your LG TV has sound but no picture or a black screen with sound, then you can diagnose the cause, and find out how to fix it, using this video.
In 60% of cases, you have a backlight failure, but sometimes the cause can be with the internal components, or even something as simple as a software glitch.
Read the full article:
https://www.lapseoftheshutter.com/lg-tv-sound-but-no-picture/