In this episode I go over a data east pinball circuit board that needed to be troubleshooted and repaired. in this video I show how to test diodes, transistors, and even go over how to solder for those that are new to electronic repair.
SR1, 2, and 3 are silicon controlled rectifiers. They act like a switch that allows current flow from the time they're turned on by the gate lead until the voltage goes to zero, or crosses zero. They typically control the duty cycle of the wave and are used in dimmer circuits as well as other circuits where they're controlling AC, or a rough DC. These appear to supply power to coils A, B, C.
Thanks for putting this out. In future you should show final product working when possible. Or ask customers to send you short clip of final item fixed and working.