Are you talking about the solenoid?
It becomes energized when a bet is made on the button deck and sends the logic signal to the processor which in turn , triggers a driver on the MPU to shoot out logic to specific IC components to release power to the solenoid...of course, the solenoid then pulls a release cam up off the stop roller ratchet gears so you are able to pull on the handle if you wish, or press the play/max bet buttons - which is wired somewhat in parallel, with the handle.
As far as I know, there's no "relay" on that line but possibly there might be a voltage rectifier IC under the tape around the the solenoid...I could be wrong.
THAT part can go bad on the gate solenoids on coin-in mechanisms on the door but usually problems with a handle working incorrectly is because of worn roller pawl sleeves, gunk in the ratchet stop roller gears, or melted rubber bushing.
On the S+ MPU, U15 (Opto, Couplr, Triac MOC3031) and Q16 (Triac 8A, 250v MAC303-8) are the IC soldered components that are open/close controls and direct the power going to the solenoid.
I don't really know how to test triacs really to see if they work correctly.
All I know is that they direct power when energized by another IC component on the MPU.
I'd have to google that and I'm pretty sure you'd have to take them off the MPU to check for operational ability.
If you want to know more about S+ circuitry, I suggest that you get yourself a copy of the Service & Parts Manual.