Owned a Black Hole for a while. During that ownership I learned how to test and replace fuses, resistors, capacitors, and diodes. Learned everything about replacing coils and mechs. Became a master at soldering to include working on boards. Achieved a beginner's to medium level of reading schematics. All in all I learned 2 big things. 1) how to find a problem in a pinball machine and 2) Never own a Gottlieb system 80 again.