I have seen a similar problem, it went away when I put an isolation transformer (Available from Radio Shack) between the Cable TV Antenna connection and the TV; apperantly a groudloop issue in my case.
Harmon Kardon + TV = no sound after 5min
I have a Harmon Kardon AVR300 receiver hooked to a Sony TV - when I try to listen to the tv through the receiver I'll get about 5-10 minutes of audio and then the receiver will shut off....if I am just playing music through a CD player or tape cassette this does not happen. Any idea why my receiver is cutting out when I run the tv audio through the receiver???