You learn a lot from other good people and Aussie Pinball.
Basic knowldege of how a machine works is highly recommended and repair involves a process of elimination similar to car repairs.
A very basic book for starters available on internet is "Pinball Machine Care and Maintenance" by B.B. Kamoroff. More specialised works require specific manufacturer manuals or system reference books.
The web and this forum are valuable for chasing up parts, referene and first hand experience.
