Hi PinballRush
at the end of Your post-1 You +/- write "want to learn about EM-Technology" - SteveFury made an excellent video - the starting of an FOUR Player late Williams (ifever You have to deal with an Williams or Bally FOUR (!!!) Player Pin:

Here http://www.ipdb.org/showpic.pl?id=325&picno=311 I read in the Backglass "Balls to Play" - this means Your pin is almost an ADD-A-Ball-Pin. In general - the only differenc between "late Williams" and "late Bally" is "Williams uses 24VAC" and "Bally uses 48VAC" - but reading the schematics is the same. xsvtoys made an excellent documentation to his true Add-A-Ball-Pin - he takes You by the hand and walks with You through everything - here: https://pinside.com/pinball/forum/topic/em-schematic-fully-described-from-beginning-to-end-bally-bon-voyage (((about stepping on the ball: do not get very deep into this "sub-sbject")))

SteveFury discusses many stuff - a collection of several different "problems" - here: https://pinside.com/pinball/forum/topic/em-pinball-circuits-basics-to-not-so-basic

From here http://www.pinwiki.com/wiki/ to EM-Games - http://www.pinwiki.com/wiki/index.php?title=EM_Repair - everything is good

From here http://www.pinrepair.com/ to 1930s to 1978 EM - http://www.pinrepair.com/em/index.htm - everything is good. Greetings Rolf