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 MIL-HDBK-1023/4
(3) If hum or vibration occurs, the input voltage is available; there may be a fault in
the remote-energizing control circuit, in the regulator, or the incoming voltage may be too low.
c) If no hum or vibration occurs, check the input circuit for blown fuses, tripped
circuit breakers, opened cutouts, and switches in the "OFF" position.
(1) If the switches or circuit breakers are in the "OFF" position or a cutout is open,
make certain that no one is or will be working on the circuits. Then close the switch, circuit
breakers, or cutouts.
(2) If fuses are blown or a circuit breaker is tripped, replace the fuse or reset the
circuit breaker only once to determine if it now holds as the regulator is energized again.
(a) If the fuse or circuit breaker holds, the trouble is over, but notate the
incident in case the device ever opens again.
(b) If the fuse blows or the circuit breaker trips again, check for any possible
overloads which could cause this protective device to fail; e.g., grounds or shorts on the input
circuit, inadequate capacity of the fuse or circuit breaker to handle the total possible load, other
loads beside the regulator which could overload this component in normal or faulty operation, or
two or more brightness relays closed or energized at the same time creating a short on the
transformer in the regulator. Only after other possible causes of this overload have been
eliminated, assume that the fault is in the regulator.
(3) If the switches are in the proper position and the overcurrent protective devices
still provide continuity, deenergize the circuit and check for opens, especially at connections,
terminals, terminal bushing, switches, circuit breakers, fuse cutouts, and input switch contacts.
Also check the taps on the regulator input for proper seating and the input winding of the input
transformer of the regulator for continuity.
(a) If an open circuit is found, make the repairs.
(b) If the tap-selector switch (if used) is not seated properly, reset the switch to
the "CURRENT" position.
(c) If the input switch contact is burned off or fails to close, then the input
switch has been overloaded or worn.
(d) If the input winding of the input transformer of the regulator is open, the
regulator has failed internally.
(e) If there are no opens in the input circuit, measure the input voltage at the
input terminals of the regulator as follows. Disconnect the input circuit from the primary supply
system and connect a suitable potential transformer and/or voltmeter (using adequate leads) to
the input terminals of the regulator. Reconnect the input voltage to the regulator, energize the
normal load, and determine the input voltage to the regulator.
WARNING:
Use extreme care in measuring high voltages. Do not come in contact with the
potential transformer, the voltmeter, or the leads, while the circuit is energized.
1. If the input voltage is present but does not agree with the taps or tap-
selector switch setting, reset the taps or tap-selector switch to correspond with the input voltage
when the regulator is energizing its normal load. Note that regulators larger than 7 1/2 kW will
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