Please help, I have a phillips magnavox 50" chassis # PTV835, Model # 9P5034 C101. When first

turned on the picture goes to a concave type with colors around a white picture and 1/2 size, and the volume would go up and down, however after being left on for about 15 minutes the picture goes back to normal, It keeps getting worse and worse The sound seemed to get worse along with the picture. I have a limited knowledge of TV's but do know electronics pretty well. I'm guessing I have a voltage problem but do not know how to diagnose the part that's bad. Can you offer any suggestions?

dana.dalbey@baytown.org