quoting from
http://arcade.50megs.com/capkit/capkit.htm"An arcade monitors control board will typically contain a dozen or so electrolytic capacitors. Over time the electrolytic dries up, leaks out, etc. and the capacitor will eventually stop working. Even before the capacitor stops working it will change its tolerance levels due to deterioration.
Bad capacitors cause many visible problems in a monitor. The monitor might suffer from ghosts, warping, dimness, blacking out, smearing, jail bars, shrinking, missing scan lines, etc. Eventually a bad capacitor will cause other components to fail also."