TV Problem

Hi
I was wondering if anybody no anything about TVs. Ive got a Sony TV and when its been on for 20-30 mins the picture starts to fade and the sound starts to fade away. If you leave on for longer the picture goes completely. Ive opened it up, blowed away the dust it was caked in and reflowed a few joints, but this hasn’t helped. I was just wondering if this was a common problem ?that some could point me towards the cause.
Thanks

Bad joints are common in Sony TV's, resolder all regulator IC's, and anything mounted on a heatsink (or with a heatsink clipped onto it). Quite often various of these are under plastic chassis supports, so you may need to take the board out of the plastic cradle it sits in.

As you didn't mention what model it is, I can't suggest anything further.