I heard small pop then lost power while watching my lg 50pg20. No red or blue lights on the power switch. What could be wrong?

You are describing a power supply defect. IT may be as simple as the main fuse. I believe the one in this set is a 6.5 amp located on the ps board right by cord connection. IF after replacing the fuse opens a second time you will need to replace the power board.
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I have recently had an issue with a dead 50PG20 LG plasma tv.
when you plug this tv in you should hear a relay click on, even before power up. If completely dead I found cold solder connection on a multipin IC in the middle of the power supply module. If you wiggle the heat sync tv may start and stop. Resolder and enjoy your viewing once again.