S 025-002
 (1)  
Remove the bypass indicator for the fuel filter (Ref 49-31-05/401).

 S 865-004

 (2)  
Supply electrical power (Ref 24-22-00/201).

 S 485-005

 (3)  
Install the test fixture:

 (a)  
Install the new packing on the filter bypass indicator.

 (b)  
Install the filter bypass indicator in the test fixture.

 (c)  
Connect the compressed air source or the fuel supply, the pressure gage, the vent valve, and the shutoff valve (Fig. 502).

TEST
FIXTURE FUEL BYPASS INDICATOR

"UPSTREAM" PORT
VENT VALVE PRESSURE GAUGE
SHUTOFF VALVE

Fuel Filter Bypass Indicator Test Schematic
A85797
Figure 502

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747-400
MAINTENANCE MANUAL

 S 865-003
 (4)  Connect the P3 electrical connector: (a) Remove the cap from the P3 electrical connector. (b) Connect the P3 electrical connector to the filter bypass indicator.
 (c)  Tighten the connector with your hand.
 NOTE:____ The connector is fully tight when you cannot see the red color band.
 S 865-006
 (5)  Remove the DO-NOT-CLOSE tags and close these circuit breakers. (a) P6 Main Power Supply Panel 1) 6K18 APU ALTN CONT (b) P83 Panel, E8 Aft Equipment Center 1) APU PRIMARY CONT
 S 725-005
 (6)  Do the test for the filter bypass indicator: (a) If you use fuel to test the filter bypass indicator, put a container under the test fixture.
 (b) (c) (d) (e) (f) (g)  Show the APU maintenance page (Ref 31-61-00/201).Move the GROUND TEST switch to the ENABLE position.Look at the F FILTER display on the APU maintenance page. 1) Make sure the F FILTER display shows NORM.Slowly increase the air pressure or the fuel pressure.Make sure the F FILTER display on the APU maintenance page shows BYPASS when the pressure gage shows 21-29 psi (145-200 kPa).Open the vent valve to release the pressure
 S 865-008
 (7)  Open these circuit breakers and attach DO-NOT-CLOSE tags. (a) P6 Main Power Supply Panel 1) 6K18 APU ALTN CONT (b) P83 Panel, E8 Aft Equipment Center 1) APU PRIMARY CONT
 S 085-006
 (8)  Remove the test fixture: (a) Disconnect the electrical connector from the bypass indicator. (b) Remove the bypass indicator from the test fixture. (c) Disconnect the pressure line from the test fixture.
 S 425-007
 (9)  Install the bypass indicator (Ref 49-31-05/401).

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747-400 MAINTENANCE MANUAL
 APU IGNITION AND STARTING SYSTEM - DESCRIPTION AND OPERATION
____________________________________________________________
General (Fig. 1)
_______
 A.  The APU ignition and starting system spools up the APU to starting speed and ignites the fuel/air mixture in the combustor. The system consists of the APU battery, APU start transformer-rectifier unit (TRU), starter motor, ignition exciter, ignition cables and two igniter plugs.
APU Battery (Fig. 2)
___________
 A.  The APU battery supplies the 28 volts dc necessary for the APU controller prior to engine start and for the turning of the APU starter. The APU battery is installed in the E33 equipment rack. For a complete description of the APU battery refer to 24-31-00/001.
APU Start Transformer Rectifier Unit (TRU) (Fig. 3)
__________________________________________
 A.  The APU start TRU uses ac voltage from the number two ac bus to supply the 28 volts dc necessary to turn the APU starter. The APU start TRU is installed in the E33 equipment rack. For a complete description of the APU start TRU refer to 24-32-00/001.
Starter Motor
_____________
 A.  The starter motor is mounted on the accessory gearbox and drives the gas generator rotor assembly through a series of bevel gears and the AGB tower shaft. The starter motor rotates the gas generator rotor assembly to provide airflow to initiate combustion. After APU ignition has taken place, the starter is de-energized. The starter motor is of the 4-pole, compound type with a series/parallel shunt field.
　
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