Is this a CRT set? CRT-based projection televisions require that their geometry and convergence be adjusted before the picture is straight and square. How much control you have over this process depends on the brand and model of TV set. Some brands only allow these adjustments in a hidden service menu that you can't get into without knowing the secret handshake. Others have a built-in feature that uses a little CCD camera inside the set which does the bulk of the work automagically for you. What brand and model is it?

If you don't have any experience adjusting the set's geometry, you will probably be able to get it "close" without professional help. But the extra step of getting it "perfect" takes special procedures by someone factory-trained as a calibrator.

As an example, I know all the service menus on my Mits set, and I know what they do, but I can only get the geometry and convergence about 99 percent there. Even with some great "secret" tips I got from a professional calibrator, I can't get the red and blue guns 100 percent perfect on the extreme edges. Now, anyone else looking at the set would think it looked perfect and wouldn't notice the variances I see, but I'm really uptight about these things.

Oh, and Andy is right. Sometimes a failed component within the set can cause the problem you describe. On my set, for example, it's a common problem for the convergence IC's to die.