mitsubishi tv powers off 2 seconds after powering on?

Sounds like bad power supply. If it comes on and shuts off immediately, and even if you do it fast, does it still come on and shut off every time? Power supply is probably the only thing that you should check out initially. Is there a thermal reset that you can hear or see on the power supply? It could also be other problem, like power transistors or a capacitor popped, but unable to check till it powers up. If dead end on power supply, do a good visual on the interior pc boards, etc, look for burned or yellowed areas on boards. Todays tvs are usually unplug a pc board and plug new one in, few troubleshoot to component level when its easier and faster for the tech to change a board.
The built in safety features are working. Most all newer tv's have built in troubleshooting, so IF you had the scanner, or can find one online, it may tell you exactly whats up, so you dont try throwing parts at it. You may not even need a scanner, sometimes there is just a simple tool I think they plug in and self diagnosis menu pops up on the screen. Of course if no display, that doesnt work. It only takes a few minutes to troubleshoot it, so most of the time is searching for parts and waiting for them to come in and be installed.
POWER SUPPLIES ARE HIGH VOLTAGE and DEADLY, dont touch anything EVEN WHEN UNPLUGGED ! Use a wooden stick or plastic handle kitchen utensil to root around in there.

Rawdawg
May 2010