Hobart 120CU20, Operation And Maintenance Manual With Illustrated Parts List

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OM-2228 / Operation and Maintenance Manual
120CU20 / Series 500120 / 400 Hz. Generator Set
October 15, 2013 Chapter 1-1
Page 17
(2) Regulated-diagnostic switch (located on the REG).
When the “ REGULATED/DIAGNOSTIC” switch is in the “ REGULATED” (down) position, the
generator output voltage is regulated by the PC board for 115/200 VAC output to an aircraft.
When this switch is placed in the “
DIAGNOSTIC” (up) position, 12 VDC is applied to the
generator exciter with the engine running at rated RPM, in order to check the operation of the
generator. This is done to determine if a particular power output malfunction is caused by a
defective generator or by a defective voltage regulator. When this switch is in the
MAINTENANCE position, no current is supplied to the generator exciter. In this condition, a low-
level, unregulated voltage of approximately 30 VAC will be produced at the generator output
terminals due to the residual magnetism of the exciter.
(3) Circuit breakers (CB1, CB4, CB7)
A 10-ampere “ENGINE” circuit breaker, protects the 12 VDC engine electrical and fault circuits,
and another 10-ampere “MARKER LIGHTS” circuit breaker protects the 12 VDC lighting system.
A 5-ampere “CONTROL” circuit breaker protects the 12 VDC control system.
(4) Digital Control PC Board [CTL] (A3)
The digital control PC board is the center for all communications throughout the entire control
system. All push-button panel commands run through the digital control PC board, which
communicates the commands to the appropriate area (i.e. other PC boards) in the control
system. The digital control PC board also controls the real time clock, monitors the over/under
voltage and overload protection, push-button panel indicator lights, generator output meters, EF
bypass switches, and communicates with the optional service tool.
Figure 7: Digital Control PC Board