Yes, neck boards are pretty easy to fix.
Unfortunately, you have blown something, so it may be harder. It may not be on the neck board now. Hell, it may be in the actual game now. When you run that much power (and AC at that) into circuits designed fro 5vdc, you have semiconductor failures through everything it's connected to.
When you watch it, does it move at all? Is it a full blue screen with no motion or flickering at all?
Do you have another monitor you could test the game with? Or another game you can test the monitor with?
Your monitor power supply is good, because you have HV. Since the screen is full, you have vertical and horizontal deflection. Since you have no black, that means your blanking circuit is good. You are left with the video processors and amps, and of course the game.
To test the game output, you have to have a voltmeter. Turn the game on and put the black probe on the connector at pin 1 (one of the grounds) and the red probe at the connector at the red, green, and blue. You should see the meter jump between .1 and 1.8 or higher volts. If you see that at the board, you have a video signal. That means the game is sending the signal. If you are getting a signal, that's excellent. It means your board is good, and you can move on to the monitor.
The next thing to do is download a manual of that monitor. There are tons of sites google will give you to get to the PDF of the manual. identify the transistors that go from the video inputs on the board to the neck board. There should be at least 2, one on the main board and one on the neck board per each color. They should all be identical. Start there. If you replace one set and it's still bad, you will have an IC issue with the video amp.
It sounds pretty involved, but hell, if you want to own games you have to learn to fix this kinda stuff. I recommend you get some chips and your PC out and watch Randy Fromm's videos on Youtube. There are 4 - two hour lectures on exactly how these things work and you can be armed. Here's the link :
CRT monitors-Part 1of 4If that doesn't work, youtube search for Randy Fromm CRT Monitors Part 1 of 4
Once you understand it, it will be clear what you need to do.