BPL
Moisture on Picture tube

I own a BPL TV (Quadra Point Focus).
During rains it catches moisture, and gradually the picture starts diminishing. Now it has totally lost the picture. I have to keep the TV on atleast 4 hrs. bfore, in order to watch a prog.. Last year I paid 1200 rs. to get this prob. solved, but come rain and the prob. is back... Can somebody help me..COZ.. i dont wanna spend thousands every year on repair...