I know this is an old post but I'm glad it's here because it helped me fix a problem with my Target Alpha. Score motor kept running so I advanced the player unit which reset the machine. Before I saw this post, I thought it was the AX acting up again.

I removed the screw and then tilted the stepper down. The piece towards the back left which is ultimately stepped when the coil fires was not advancing the cam. A small small drop of lube on it allowed it to move correctly and advanced the cam.

One thing I always do is check the manufacturer rather than the specific game because many parts and solutions are similar.