I've been working on a friend's Bally Fireball, and after replacing the 100 and/or 1000 pt bell solenoid (the old one locked on and melted), he was noticing a buzzing of the bell (the plunger striking the bell rapidly several times) - similar to that of an old-fashioned phone - when a ball would move over a switch slowly. Looking at the schematic below, I understand that both the 100 and 1000 pt relays (which control the bell solenoid) have a locking switch which keeps the relay on, in series with drum unit EOS switches that open the circuit when the plunger for the drum unit has completed its motion. But if the ball (or my finger) keeps a switch closed that activates either of those relays, there's nothing to turn off the relay, correct? As long as the ball is keeping a switch closed, the EOS switches don't matter - the relay stays powered on and the drum unit plunger stays pulled in, and the bell coil stays powered on - is that right?
If so, then a buzz on an AC bell coil would be normal behavior?

When I replaced the bell solenoid, the replacement coil was just ever so slightly taller than the old coil - we wound up having to move the upper bracket that holds the coil up just a hair, resulting in the upper end of the coil being slightly higher (and thus closer to the bell) than it was originally. So the plunger is slightly deeper in the coil when it strikes the bell than it was originally. Could that be causing an increased buzz? I wonder if raising the bell slightly would matter.

If that was clear.....any thoughts?
Fireball 100 and 1000 pt relays (resized).JPG

Thanks Mark - I wondered if the plunger wasn't able to get high enough to avoid hitting the bell as it oscillated. The bottom bracket holding the bell solenoid is welded to the frame, so I don't think I can lower the solenoid - I'll rig something up to raise the bell then, and see what happens.

I also wondered about putting a diode (and resistor?) in the bell solenoid circuit to effectively change it to dc...would that be wise? I'm sure a DC solenoid plunger oscillates too if able to move freely, but because this one buzzes for as long as the switch is held closed, I'm assuming that it's the alternating nature of the current that's affecting this.

Is it a smart design to allow the bell (and drum unit) solenoid(s) to lock on like that? Those things (especially the bell solenoid) are high current and get really hot very quickly, so if you had a stuck switch under the pf, or a ball got stuck in a position where it was closing a switch, it seems like you could burn out one of those solenoids pretty fast if no one was there watching the machine.

Thanks, Mark - sounds like I need to adjust the height of the bell then to try to find a place where the plunger doesn't oscillate so much after the rebound. Thanks for the input, as always!