Hello magicbrainz,
There is a possibility that the protection circuits are shutting the TV down. There's either
an over voltage fault or the fault lies in the protection circuit itself.
Firstly, prior to the set shutting down, check the voltage on the main filter capacitor.
Next, you need to check the main HT rail from the power supply. Though you really need
to find out its value for a more accurate evaluation.
You can also disable the HT rail, then fit a 100W globe across that said rail to determine
if its a PSU problem or a fault with the rest of the set.
Can you please provide us with the model number of your telly? I might be able to find a
schematic of the power supply at least.
Regards.
Relayer