If they've all stopped working at once, I'd check for a broken return-wire that is common to them all. You can have all the voltage in the world applied to the units, but if there is no way for the current to get back to the supply, there will be no work done. A quick check would be to measure the voltage across the sw motor itself; no voltage means no current. If there is voltage on the unit from the supply, the common wire is off. Do NOT measure Ohms unless all the power is off.... You'll blow your meter!
Have fun.... George
If you could post a wiring diagram, some of us could probably point you to the likely areas of failure.
Karl
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