Generally speaking a convergence problem will show up as a picture that appears like a 3D image with a bowing from the top and bottom. If this describes the problem, then try resoldering the pins on the convergence ICs. If that fails to resolve the problem, replace the ICs. These are large black ICs attached to a heatsink that should be marked STKxxx.

Keep me posted.
Dan

P.S.

I am sorry about the late response. With the site changes, the questions aimed directly to me were no longer on the initial page and I was not aware of this.