the documentation is here:
if your control unit is stalling due to sticky clutches, ya might as well stop and deal with it. The game won't work properly and you are risking cooking the stator winding or damaging the gears in the gearbox.
the general sequence for an unmodified game is:
1] turn on game and it resets the credits
2] deposit coin. Game cycles and it may or may not add credits depending on configuration of wiring to multiplay relay. During cycling, the playfield shutter opens and many switches on the shutter cams reset a bunch of the units. Timer cam switches may step some of the units immediately.
3] the first ball is raised. The timer unit steps up once
4] you play additional coins/credits to enable more cards and the features after the 6th coin
5] you eventually shoot the first ball. When it exits the runway, the ball lift motor turns on and raises the second ball. The timer unit steps to the second step and the playfield shutter closes (this happens while the first ball is rolling around the top of the playfield arch).
6] after shooting four balls, the R button is enabled to allow scanning for wins. If a win is detected, the game pauses and lets you choose to collect the win or try for double-or-nothing.
the features modify the doubling stuff a bit, but that's the general idea of what happens. When the playfield shutter is not closing, usually it's the timer unit not stepping. Common reasons are poor plug connections or dirty/misadjusted switch on ball lift cam, or especially dirty/misadjusted open-at-top switch on the side of the timer unit.
'course, if the shutter is never closing, then it's never opening again and the timer unit may not be getting reset. If you tilt the game so the tilt trip relay trips, the shutter should close.