Help w/ weird big-screen tuning issue?

I just purchased a used Sony KP-61HS10 61" RPTV. I also have a smaller, older Sony set. Last night, I was watching the ballgame on the small set, thought I'd fire up the new one, see how it looked. I hooked up the cable to the RPTV, picture looked great, I switched to the very same channel that I had been watching the ballgame on the small tv, and voila...no ballgame! In fact, instead of TNT, I got the Food Channel! Two tvs, same cable, no other electronics attached or involved. The "local" channels, 1-13 were identical on both sets, but beyond that, I had many more channels appearing on the small set than on the RPTV. Also, if this is any clue, the Food Channel (which appeared where TNT should have been) was a poor quality picture. Any idea what's going on? Thanks! Ben