Picture goes off after 30 sec

@tim3g this could be power board issue as well as a mainboard or backlight issue. A common failure symptom of a defective inverter circuit (this will depend on which boards your TV has. Again, pictures will be great) is momentary operation with a panel flash then complete shutdown. You did not tell us what you have checked. You also want to let us know if the picture returns immediately if you turn the set off and then back on, or if you will have to wait a bit. I'd suggest that you unplug the set and remove the back from it. Then check your boards for any obvious damage like bulging, leaking capacitors etc. Post some images of all of your boards with your question. That way we can see what you see. Use this guide Adding images to an existing question for that.