Just had a call recently on Westinghouse ERL with linear operator doors slamming open and closed. Checked the standard things, switches etc. But couldn't find a culprit. Started to focus, under advice of another tech, on the diodes mounted on top of resistor/switch box for door operator. One had been cut out of circuit and bypassed, so in turn, I cut out bypassed the other one. They are labeled in wiring diagram as Z1 and Z2 , so I assume they are zenner diodes. I know that zenner diode are used to drop a certain set amount of voltage,that said, I don't understand why they are used in shunting around door motor armature when they are already using a resistor in series. I don't see any reason to track down part and reinstall in circuit since doors are working fine enough, and this equipment is overdue for mod.

Mainly just curious why Westinghouse engineered it this way in the first place.

Also figured out that open resistor bands actually controlled close speeds, and vice versa. Someone in the past told me that this is common.

I'm comfortable with Dover and Otis relay logic, but Westinghouse makes me want to pull my hair out sometimes.