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Question: Audio Only HD channel

I receive my HD channels directly via my Charter Coax cable. I do not have a cable box. On two of my HD ready TV's I can receive ABC, CBS, Fox, and NBC without issues. However, on this model of TV (46z4100) there is no picture for the NBC channel. When I turn to that channel I hear the sound, but a small popup
windows states "Audio Only". I have tried readding my digital channels, but no luck. Any ideas?