PANASONIC - TH-42PX75U TH-50PX77U LED BLINKS ONCE AT A TIME

FAULT:
"A" board is defective. Communication error.

Disconnect AC power to set, and disconnect [A5, A6 & A7] from "A" board.  The TV should turn ON automatically, and display a white screen.  If so, make sure that "A" board should be replaced.