[Ronbo]

Long ago (over 10 years) we had a 50" Hitachi projection TV that started doing exactly the same thing, and I compensated by increasing brightness and contrast until I hit the maximum settings. The picture slowly kept getting darker until it became unwatchable and I just replaced the set. It wasn't dirt on the projection lenses as I kept them clean. In short, it's dying and the fix is probably more costly than the set is worth.