This is an 8 year old TV but it has an otherwise great picture and would like to fix it if possible. The issue that I'm having is that the picture keeps blacking out and then reappearing. It can happen 100 times in a minute or just once and then stay black. If i give it a good WHACK on the side, the picture is restored, usually until I turn it off.

The frequency of this problem seems to increase over time. When I get too fed up with it, I remove all the screws and slip the tube and circuitry out of the case. When it is in this open state, I cannot reproduce the problem via poking and prodding (with a wooden stick), and when I put it back together, the problem won't reappear until weeks or months later. And then the sequence repeats...

I'm not expecting miracles with this discription, but does anyone have any ideas what might be going on? I don't know anything about TV electronics (but could probably replace or solder a part if I knew what was causing the problem) and am just hoping that there is something obvious that someone may be able to pin point. Thanks for any help...