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OM-2084 / Operation and Maintenance Manual
90CU24 / Series 500392 Generator Sets
f. Re-checking the entire unit after testing
(1) With the engine running at normal governed speed, check the entire unit for vibration and for any
parts which may have become loosened during the above checks. Tighten any loose attaching
hardware as required.
(2) Check engine oil pressure at rated speed (2400 RPM). The oil pressure gage should indicate at
least 45 psi (310 kPa) when engine is hot. Also at rated speed, check engine coolant
temperature. The needle in the temperature gage should indicate in the range of 180° F to 200°
F (82.2º C to 94º C), depending upon ambient temperature.
WARNING
(3) Check 400 Hz generator bearings. Use a stethoscope or metal sounding rod to listen for
unusual noises. If using a metal rod, place on end on the generator housing and hold the other
end near the ear. Hold the rod with three fingers and use the index finger and thumb to form a
sounding chamber between the rod and the ear. Do NOT allow the rod to touch the ear. Listen
for grinding or pounding sounds which would indicate a defective bearing. An engine noise may
be telegraphed to the generator and misinterpreted as a generator noise. Send the unit to
overhaul if in doubt of bearing serviceability.
Generator Set Adjustment
3.
a. Generator Adjustment
The 400 Hz generator is a brushless type requiring no adjustments of any kind.
b. Adjust 400 Hz voltage regulator.
When a voltage regulator is first put into service, or when output (generator-to-aircraft) cables are
changed, the regulator may require adjustments of output voltage value and line-drop compen-
sation.
For making these adjustments, the voltage regulator has three potentiometers:
• Coarse output voltage potentiometer
• Fine output voltage potentiometer
• Line-drop compensation potentiometer. See Figure 1, Sheet 2 for identification of
components used for regulator adjustment.
For regulator adjustment, the generator set must be running at rated RPM, under no-load conditions.
(1) Adjustment
a. Adjust Voltage Control
The output voltage at which the generator is regulated is adjustable by the PC board fine
output voltage adjustment potentiometer (36, Fig. 1). Turn the potentiometer adjustment
clockwise (cw) to increase generator output voltage, and counterclockwise (ccw) to decrease
voltage.
Observe the output voltage as indicated by the voltmeter which is located on the control panel
of the generator set. Set output voltage at 115-V AC line-to-neutral (200-V AC line-to-line).
b. Adjust Line Drop Compensation
Adjustment of line drop compensation is made with the line drop compensation potentiometer
(38, Fig. 1). Turning the potentiometer knob clockwise increases the magnitude of the
compensation, and turning the potentiometer knob counterclockwise decreases the
magnitude. To adjust the line drop compensation, proceed as follows:
November 27/1997
If a metal sounding rod is used to detect bearing noises, exercise extreme care
to avoid injury.
Chapter 2-3
Page 9
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Table of Contents
Troubleshooting
