I assume the monitor is a Sanyo 20EZ. That's the monitor that came in most Nintendo upright arcade games.
A picture of the screen would really help us understand what the issue might be.
But if I had to take a stab at it...I'd say you are definitely in need of a cap kit if you haven't already done one. The capacitors on that chassis are 35 years old and must be replaced. If that doesn't fix it then I'd turn my attention towards the flyback.
HOWEVER, this is assuming you have already tried adjusting the following:
- Brightness pot on the remote board
- Sub-brightness on the center of the chassis (careful with this one while the monitor is on)
- Screen pot on the flyback itself.
It would also be a good idea to make sure you B+ is set to 108VDC. THIS IS A MUST! SUPER IMPORTANT
Again, Sanyo Flybacks are relatively reliable so don't worry about that until last.
Also, you MUST watch Buffett's video on calibrating a Sanyo. It will teach you alot about how the colors work and what to adjust and in what order. Also how to adjust the B+
Roll up your sleeves...you are going to need to become familiar with everything on this chassis.
Just a little hard to make an assessment without pictures of everything first.