Why do my AD300 and PS904 shut down when I plug in a Handheld Device?
Assumption: The AD300 chassis/body is connected to earth ground via a grounded metal door frame and/or strike.
If the positive side of the power supply (+) becomes shorted to the lock body due to a pinched or nicked wire:
1. The positive side of the power supply is shorted to earth ground through the metal door frame/strike;
2. The lock will operate normally as long as no HHD is connected, since power supply negative and earth ground are isolated;
3. When the USB plug is inserted into any of the AD300 units connected to the power supply:
a. Earth ground is connected to power supply negative;
b. The positive and negative power supply terminals are shorted together;
c. The PS904 shuts down due to an overcurrent condition, taking down all connected locks.
4. Disconnecting the USB plug from the lock removes the power supply short and restores normal operation.
The power supply short to earth ground could occur in any of the connected locks, in a grounded metal conduit, or in an electrified hinge; the end result is the same.
The power supply short to earth ground could be a resistive, rather than a direct, short. This could result in erratic lock/power supply behavior before total shutdown.
In a normal configuration, the resistance between the positive power supply terminal and the lock body/earth ground should register as infinite when measured with a digital multi-meter.
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