Lost sound in left channel of jukebox. When machine is in non-playing mode I hear hissing coming from the speakers. When a song is selected, the hissing seems to stop but get no sound. Right side plays OK. When I cut power to the unit I hear a loud "pop" through the speakers. I believe the problem is in the CD interface board (#56877-A) on the front of the player. I have 3 of these boards, each has a different issue. I replaced the cable from the board to the amp with no improvement. Anyone out there who has a working board, or can repair mine?