How the pop bumper driver board fires its coil
When the cup switch closes it triggers a 74121 one-shot; the timed pulse is buffered by a 7416 and switches a Darlington power transistor that grounds the coil. The coil on-time is set by the timing resistor and capacitor on the 74121. Every pop board is the same and any one can replace another.
Systems
Related tips
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Source: System 80 Service Manual, Gottlieb