Did you reflow the solder to the sync pin?
I am assuming that this is a Sanyo 20EZ since it is a Nintendo cabinet. I just did a capkit on my Donkey Kong machine last night in fact.
The EZ in 20EZ does not stand for "easy" as far as cap kits are concerned. Might as well reflow sync pin solder and do the cap kit while you have the monitor boards out of the cabinet. Just take your time removing the monitor boards (you will have to also remove the transformer, audio amp, adjustment pot board, and neckboard)
Not knowing whether it is the game board or the monitor the first step is to replace the monitor caps and reflow cold solder joints. The reason for this is because it is $10 and a couple hours of labor. If we can fix it with minimal effort then great. If this doesn't fix it then at least your monitor now has a new cap kit!!!
Troubleshooting the gameboard opens a whole new can of worms.