Hi Tom
Not the check detection bar but the coin detection bar may need to be adjusted, if the machine is complete it should have two horizontal bars on the escalator and two vertical bars on the mech, the lower bar is for the coin detection and has a small screw that holds a pin that senses the coin and will allow the handle to be pulled down, if that is even a little bit out of adjustment you wont be able to pull the handle.
Try this before you go and make all bunch of adjustments, wile holding the bottom horizontal bar from going forwards with your fingers, pull the handle and see if the machine plays, if you can play the machine than just loosen the screw and adjust the pin out a little bit, small amounts at the time, the upper check detection bar is not needed for regular play.