Learn basic board repair before working on these boards
These boards are easy to ruin by clumsy soldering, and many repair shops refuse to touch a board that has already been botched at home. Practise soldering and desoldering on scrap boards first, or send the board out.
Systems
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part One, Clay Harrell (pinrepair.com)