Same problem here. I bought same LG model two years ago ( so is out of warranty) and last week suddenly the image became scrambled and after few seconds the image was distorted .
I turned it off, disconnected network cable and unplugged power cord for few minutes. When I turned it on the tv tuner won't pick up channels.
I updated firmware of the tv, no change. Restored factory settings, same problem.
I took it to a friend who works at a TV repair service and the problem was with the tuner. He had to weld again the tv tuner on the main board.
That solved half of the problem. Now I can watch analog tv channels but digital tuner doesn't work: the image is scrambled.
If you found other solution, let me know.