I've got a Batman 66 here that refuses to start multiball. With locks lit, shots into the lock will correctly register the first two. The third ball goes in, and rather than awarding it, the game completely loses track of the ball and goes into wait-and-hunt mode, periodically spinning the turntable and cycling the coils. It never starts multiball, though with three balls locked, you can often start it yourself by flicking them with your finger.
The three lock switches in the turntable are working - both with fingers and with balls. (Hmm - I guess that could have been phrased better.) As far as I can tell, the problem is that when all three balls are in the lock, and the lock post is up, they're packed so tightly that the ball furthest from the post (lock 1) actually lifts up enough to deactivate its switch. There seems to be no way to adjust the length of the lock lane. Either this, or a software error.
Before I go bending brand-new switches around to try and get it working, has anyone else experienced / solved this behavior? I couldn't find anything on it in the forums or the Stern website, but it feels like the kind of thing that might be a known issue - hence this post.