Old TV's (Sony's especially in my experience) suffer from dry soldered joints, often resulting in symptoms similar to this.
It can be a time consuming repair. So on a 15 year old TV I'd ask for an estimate first.
Sometimes, dry joints or especially crystallized joints (often found in the power supply), can cause overheating, resulting in carbonized printed circuit at the joint. This is potentially dangerous, so it's important that only a qualified person inspect the TV or carry out any repair.
Cobweb, January 2005