TM 11-6125-220-20
Table 3-3. Troubleshooting (cont.)
Possible cause
Malfunction
Corrective action
b.
Readjust increase volts adjustment resistor
b.
Misadjustment of increase volts
as described in paragraph 3-9.
adjustment resistor.
a.
a.
Ac output voltage is high . . . . . . . . . .
Dc input voltage is higher
Check dc voltage at power supply and correct.
than 30V.
b.
Readjust as described in paragraph 3-9.
b.
Misadjustment of voltage
adjustment resistor.
c.
Refer inverter to higher category maintenance.
c.
Regulator failure.
Refer inverter to higher category maintenance.
Misadjustment of internal
Speed (frequency) is too
frequency adjustment resistor.
high or too low.
a. Check and tighten connections as necessary.
a.
Loose connections.
Output voltage unstable . . . . . . . . . .
If trouble persists refer to higher
category maintenance.
b. Check and refer to higher category
b. Poor commutation or poor
maintenance.
brush contact at sliprings.
Refer inverter to higher category mainte-
Misadjustment of increase
Speed (frequency) is too
nance.
high or too low.
adjustment resistor.
a. Check and tighten connections as necessary.
Output voltage unstable.
a. Loose connections.
If trouble persists refer to higher
category maintenance.
b. Check and refer to higher category
b. Poor commutation or poor brush
maintenance.
contact at sliprings.
3-8.
Maintenance.
3-9. Output Voltage Adjustment
Periodic inspection of the ac contact brushes is the only
The VOLTAGE adjustment (fig. 1-1, 1-2, or 1-3) is ad-
maintenance performed at the organizational level. This
justed to provide 115-volts ac output, Follow the pro-
inspection may be performed in the aircraft if the inver-
cedures given below.
ter can be reached easily. Otherwise, remove the inverter
a. Turn on the necessary aircraft switches to start
as described in paragraph 2-4.
the inverter. Set the AN/URM-105 range to 1000 AC
WARNING
VOLTS and connect the test leads to the test point jacks
If the inverters are located in the nose of a
on the front of the inverter regulator housing. Note the
helicopter, adjustment of the VOLTAGE con-
output voltage reading.
trol must be made with the aircraft engine in-
operative and an auxiliary power unit (apu)
b. Loosen the locknut on the VOLTAGE adjustment
connected as the source of aircraft power.
shaft. Using a screwdriver, turn the VOLTAGE adjust-
Should an apu not be available and the air-
ment shaft clockwise to increase the output or counter-
craft engine required to be operating for po-
clockwise to decrease the output voltage until the AN/
wer, access to the inverters must be made
URM indicates a reading of 115 vac.
through the nose compartment access door to
c. After adjustment has been made, tighten the lock-
keep the person making the adjustment clear
nut on the VOLTAGE adjustment shaft. Disconnect the
of the aircraft flight controls.
leads of the AN/URM-105 from the inverter. Turn off
the aircraft switches to remove power from the inverters.
3-4
