I have recently been given a 21" Sony (Compaq badged) Monitor Model
M50LMD15X. Date of manufacture of this unit is September '98. I think most
recent Sony 21' have pretty much the same internals sparing a few changes
here and there.

The problem with this unit is that the picture jitters up and down the
screen constantly, with temperature and a good whack having no effect. I
have checked the power supply and it seems fine with very slight variations
in voltage (.1V on the +/- 15V rails etc). Had a general inspection of the
deflection board and no obvious blown components

Im thinking a capacitor is breaking down under load with my next step being
to replace all the electrolytics in the vertical defection circuit. A good
idea? or any other suggestions?

Cheers,
Shaun