Some time when you have closed caption active like text1 or text2, and the broadcast have other format like cc1, cc2, you only get the black square in the screen (but you have a partial video , outside of the square and perfect sound), because you TV set only can decode part of the signal and is waiting to receive more data to show in the screen. Try to turn off the c.c. feature, and see what happened. Good luck. Bye.