JPS,
The capacitor discharge unit itself is the means to keeping switch machines from getting sluggish. If they still don't snap well after inserting one of them in the circuit, like the Miniatronics PDC1, then you have a substantial mechanical problem with the machines, and/or linkages and points as well.
Miniatronics has not posted its instruction sheet for the PDC1 online, and I don't personally have a paper copy to review it, but your hunch on supply voltage is likely right on target.
What it has published is this:
Click here for more: Miniatronics Super-Zapper Capacitive Discharge Unit)
As a rule of thumb for all electronics I wouldn't go more than 10% over the recommended operating voltage in order to be safe (and many people say 5% to be extra safe).
As a result, applying 20 VAC probably killed it.
And, it would be a good idea to check out the mechanicals of your switch machine installation before proceeding with replacing your PDC1.
Mike
