I have a Zenith A27B33W. It about 8 years old. Its always worked great until it sat for a season. I auto programed the tv and it say it found 78 channels but they are all the same tv station. I hope you can understand what I am trying to say. It is very weird. And by the way it sucks watching the same channel.
This TV set sounds like the tunning voltage is stuck on one voltage. It is going to be a tuner problem or a problem in the PLL circuit. It uses a 9-1999 module, but Zenith says its no longer available. You could most likly get it repaired, but do you really want to invest maybe 150 bucks or so on a set this age? Please let us know if you got the set fixed and what it took to fix it. Good Luck