John Gill wrote:

Dave:
I have had some experience with this problem on Dell/Sony GDM-17SE2T
monitors. Behind the flyback, there is a small transformer in location
T403. Mine had the number 998-11 on it.
These transformers develop small cracks in the core that is on the
outside of the windings. This somehow affects the horizontal width.
I had two monitors with narrow widths. Replacing the transformers
with ones from junked chassis fixed the problem.

ARRGGHHH!! I had high hopes for this but unfortunately replacing the
relevant T403, (which had a cracked core), hasn't resolved the problem -
the raster is still 50-60mm too narrow, so back to the drawing board.

Dave