Read http://www.shopjimmy.com/tv-repair-tips and try AVS Forum or whatever forum you find replies from any techs.
I have a 55 inch LG Smart TV. A few days ago our tv started flashing on and off. Once turned off and back on with the remote, the bottom of the screen was dim but we were able to watch the tv. It did that for a few days and now, once it is turned on the picture is perfect for 3-5 minutes and the picture goes black but we can still here the sound. Any suggestions as to what is causing this?