Capacitor kits (or capkits) will usually fix these problems/symptoms:
Blacking out (intermittently going dead/no video)
Uneven brightness across the face of the tube
Washed out picture
Darker than normal picture
Some focus/smearing problems
Geometric distortion ("keystoning/pincushioning")
Bars or dark bands ("jailbars")
Color edge bleeding
Lines or squiggles in picture
Horizontal and/or vertical hold problems
Most capkits cost around $10 and contain between 12 and 20 electroyltic capacitors to replace the known problem causing ones on you particular brand & model of commercial arcade video monitor. Zanen Electronics (phone: 806-793-6337) in Texas sells cap kits as does Bob Roberts.
Capkits will NOT fix:
Picture tube burn-in (that's a permanent condition that only replacing the picture tube with a brand new one will cure)
A bad yoke or flyback
Picture tube (a.k.a. CRT) with weak/bad cathodes, burnt out filament, internal shorts, or bad focus. For this type of trouble the picture tube needs to be connected to a "restorer/analyzer" like the B&K model 467 to test it's condition. If the tube is found to have a repairable condition then the restorer/analyzer can 'zap' new life into the tube.