wow, that's a new one to me.
Just changing that cap wouldn't do something like that. Most of those caps just help filter and smooth out the power going to certain systems.
the only time changing a caps value really matters is for timing circuits.
They can affect the timing pretty bad.
this looks like perhaps a video amp issue (lm1203n i believe) it's on the neck card. I can't think of anything on the deflection board that could cause a white band to scroll on the screen like that.
perhaps "rickn" could help you out better.