Start by checking the vertical deflection yoke resistance. It should be about 55Ω. While you are at it, inspect the yoke connector on the board. If nothing obvious, and if you haven't already, clean off the old solder and resolder them.
If all seems to be okay, check the voltages on the vertical output transistors, X401 and X402 (I've attached a file with the GO7 voltages in case you don't have that info).
If they are way out of tolerance, you are getting closer to figuring out the problem.
Welcome to the fascinating world of CRT arcade monitor troubleshooting. You have a great, simple, chassis to begin learning with. Don't give up!