It's a slim shot, but you might try (when powered down) measuring resistance
from the output side of all voltage regulators and rectifiers looking for a
short to ground. (Often the rectifiers are TO-220 packages).
Saved my ass once recently. A Samsung plasma with power supply issues - and
the board no longer available from Samsung. Robbed a TO-220 rectifier of the
same type off a scrap board.
Mark Z.
A common cause of this problem is a shorted sustain card. This
appears to use an LG panel. One troubleshooting method on these
panels is to unplug the TV, disconnect the cable linking the power
supply to a sustain card, then plug the TV in again and see if the
power supply turns on. If that didn't help,disconnect the next
sustain card.
PlainBill