MAINTENANCE OF THE CONTROL BOX ASSEMBLY
All the controls and instruments necessary for the
operation of the generator are contained in the control
box. These controls and instruments include the
voltage regulator, frequency converter, variable resis-
tor, interference suppression components, terminal
board, and the necessary wiring harness.
8-2 Control Box (AC Unit)
a. Removal and Disassembly.
(1) Remove the control box (para 6-3).
(2) Refer to figure 8-1 and disassemble the con-
b. Cleaning and inspection.
(1) Clean all parts thoroughly.
(2) Inspect all parts for signs of burning or over-
heating and for cracks, breaks, defective threads, and
(3) Inspect the variable resistor for proper oper-
ation and for proper resistance. Resistance should
vary smoothly from 0 to 1,100 ohms ± 20% when the
unit is turned through its range. Replace a defective
(4) inspect wire leads for breaks, poor connec-
tions at the terminals and for broken or frayed insula-
tion. Replace defective wire leads.
(5) Inspect the voltage regulator and transducer
for cracks, signs of overheating, and other damage.
Replace a defective voltage regulator or transducer.
Apply one coat of clear varnish meeting
specification MILV-173 to the exposed cir-
cait area of the voltage regulator and trans-
(6) Inspect the frequency converter by compar-
ing with a unit known to be good.
(7) Replace all defective parts.
c. Assembly and Installation.
(1) Refer to figure 8-1 and assemble the control
(2) After the assembly of the control box, apply
one coat of clear varnish meeting specification MIL-
V-173, Type II.
(3) Install the control box (para 6-3).
d. Test. Test the AC control box components as
(1) Frequency meter.
(a) Remove load cables and start the genera-
(b) With a multimeter, measure DC current
across the terminals of the frequency meter. This read-
ing will be in DC micro amps. Reading at minimum
deflection of the frequency meter (55 Hz) should be 0
micro amps. Reading at maximum deflection of the
frequency meter should be 200 micro amps. Normal
reading at 60 Hz should be 100 micro amps ± 10%(90
to 110 micro amps).
(c) If reading is not within specifications, stop
the generator set and connect a frequency meter of
known accuracy in series with the set frequency meter.
Be sure to observe polarity.
(d) Restart the generator set and compare
reading on the set meter and test meter. Frequency
variation of test meter and set meter should not exceed
(e) If frequency variation exceeds 1% of full
scale valve (1 Hz), replace the frequency meter.
(f) Disconnect frequency meter used for test.
(2) Voltage regulator.
(a) Select desired voltage setting on the
voltage changeover switch (120 V or 240 V) and start
the generator set. Load cables should not be attached
to the output terminals.
(b) Using a multimeter, check voltage across
output terminals to verify reading on set voltmeter.
If the voltage is low and adjustment of the vari-
able resistor will not correct the deficiency, check
the exciter voltage across terminals 5 and 6 of the
voltage regulator. This voltage will vary but should be
about 25 volts. If no voltage appears on