Why is screen black still audio ok

ALOK SHARMA “screen turns black sometimes suddenly” could be an LED backlight issue. LG has had trouble with bad backlight strips. This “sometimes after getting horizontal lines falling one upon other” is not a backlight issue but would be a panel issue. You will need to let us know the exact model of your TV and take a look at the boards. Measure the power output from the power board to the LED’s and see if that voltage is correct. Measure when you have a picture and when you have none. Check for any obviously damaged looking components, as well as burn marks etc. Post some good pictures of what you see with your QUESTION. That way we can see what you see. Adding images to an existing question