Low contrast, dark picture with washed out color or colors missing?
If so, I see these symptoms often with customers adding external equipment eg. DVD, digital receivers to older TV's. If so, check your AV connections are secure and any RGB settings are compatible with the TV. Alternativey switch equipment to composite Video output in their set-up menus or use RF connection instead if available to determine if problem is with AV connection.
Otherwise, depending on model could be IF or RF modulator instability (often dry joints in older Sony/Mitsubishi 4:3 sets), or less often video processor failure.
Cobweb
November 2004