after an hour screen goes blank but sound still on.need to unplug tv

Chris Teago  while the screen goes black but you still have sound shine a flashlight beam at an angle against the screen. Check to see if you can make out shapes and silhouettes. If so you know it is your backlight. If not then you will have to measure the output from your main board to your power board as well as the voltages on your LED connectors. If you let us know what model your TV is (Philips love to use Chassis numbers so let us know that as well) and post a couple of good pictures of your boards we can try and help you to narrow it down