TM11-6125-256-34
Section II. IN-AIRCRAFT MAINTENANCE
3-5. Operational Test
An error in output frequency could result in
the aircraft being several miles off course over
a long flight period On the 4B48-6-A, en-
b Power Requirements Connect an external power
sure that frequency adjust resistor R15 is
supply to the external power connector on the aircraft
set to the proper output frequency as de-
while making the operational test (Refer to the appli-
scribed in steps (7) and (8) below On the
cable aircraft technical manual) The power supply
4B93-1-A, this adjustment is not made so
must be capable of delivering 285 amperes at 27 5
perform only step (8) below
volts dc
c Procedure
(7) On the 4B48-6-A only, apply a full load
(1) Turn the main power and other appropriate
and turn frequency adjust resistor R15 through its full
switches in the aircraft to the ON position Check to
range No variation should occur in the range specified
see that the motor-generator starts and that the aircraft
in step (6) above Turn off the aircraft components
dc voltmeter reads 28 volts
and reset R15 to provide a 400-Hz output
(2) Plug the prods of electrical power test set
(8) Turn on the aircraft components, one at a
AN/UPM-93 into the motor-generator test joint jacks
time, until the motor-generator is fully loaded Voltage
(fig 3-1) Remove the control box cover
variation between no load and full load must be less
(3) Adjust the AN/UPM-93 range selector to
than 5 volts The frequency variation must be less
the 150 position
than 20 Hz from the 400-Hz setting
(4) Operate the motor-generator at no load (no
ac components of the aircraft operating) Loosen lock-
NOTE
If the voltage and frequency outputs are not
nut on voltage adjust resistor R14 or R23 as applicable
within the limits specified in step (8) above,
(fig 3-1) and turn through its full range Voltage indi-
the motor-generator must be removed from
cated on the voltmeter of the AN/UPM-93 must not
be less than 110 or more than 120
the aircraft for maintenance
(5) Apply a full load to the motor-generator by
(9) Upon completion of the operational test, re-
turning on all the aircraft equipment that operates from
move the AN/UPM-93 prods from the motor-genera-
the ac supplied by the motor-generator (Refer to the
tor Turn off the aircraft master switch and disconnect
applicable aircraft technical manual) Repeat the pro-
the external power source from the aircraft Replace
cedure given in step (4) No variation should occur
the control box cover
in the adjustment range specified Turn off the aircraft
ac components and set voltage adjustment resistor R14
In-Aircraft
Troubleshooting
Table
or R23, as applicable, so that a 115-volt output is indi-
cated on the voltmeter of the AN/URM-93 Tighten
If the operational test of paragraph 3-5 indicates a
the locknut
malfunction, localize it, using in-aircraft troubleshoot-
(6) On 4B48-6-A, operate the motor-generator
ing table 3-1 If the procedures in the table fail to
at no load and turn frequency adjust resistor R15 (fig
correct the fault, or if a malfunction not mentioned in
3-1) through its full range The limits, as indicated on
the table is noted, remove the motor-generator from
the frequency meter of the AN/UPM-93, must be
the aircraft and bench test as described in section III
