Clay's articles are a real boon in helping you fix a machine, EM or otherwise, but the late Russ Jensen also produced a really good book on how to fix EMs and how to read a schematic. Like many pople, schematics were little more than hyrogliphics to me until I read, and kept re-reading his book until I finally grasped what he meant.
The golden rule to an EM machines' working is the 3 part one: Power, Switch, Load; i.e the 25v power supply [to a coil for instance] through to a switch [flipper button etc] then onto the load, the solenoid or coil. Of course, not all machines circuitry share such a simple route, as other items can also be linked-up which can cloud a fault finding exercise, but so long as you stick to the principle, you wont go far wrong.
And of course theres one more tip: Dont be tempted to adjust switch contacts unless its really necessary! A better bet is to just tighten the screws that hold the switches onto their mounts because once a machine warms up, things tend to expand. If you've just 'adjusted' a switch and then your machine begins to play up after an hour or twos play, thats what youve done wrong. Tighten the screws, THEN check the adjustment.
