I have a Panasonic TV, about 15-20 years old, which works great except that the screen, after being on for a while, occasionally collapses to a very bright line across the center, showing all colors as if the video is all there in that one line. If I cycle power, it goes back to normal. Sometimes it goes back on its own after a few seconds. Does this mean it’s nearing its end of life? Is there anything I can do to improve it (I’m not going to open it up)? We watch DVDs mostly, but it seems to happen regardless of source, maybe once or twice in several hours of being on.