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(d)  
Attach a DO-NOT-OPERATE tag to the APU master switch on the P5 forward overhead panel.

 (e)  
If you found air leakage, repair the cause of it.

 S 794-010
 (4)  APUs WITHOUT ALLIEDSIGNAL SB GTCP85-49-7096; Examine the check valve for leakage:
 (a)  
Start and operate the APU (AMM 49-11-00/201).

 (b)  
Do the APU usual shutdown (AMM 49-11-00/201).

 (c)  
Attach a DO-NOT-OPERATE tag to the APU master switch on the P5 forward overhead panel.

 (d)  
Visually examine the check valve and the air line connection for any signs of leakage: 1) If you found signs of air leakage, repair the cause of it.

 S 414-009
 (5)  Close the APU cowl door:
 (a)  
Disconnect the door support rods.

 (b)  
Put the door support rods in the clips on the APU cowl door.

 (c)  
Close the APU cowl door.

 (d)  
Close the latches for the APU cowl door.

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APU IGNITION AND START SYSTEM - DESCRIPTION AND OPERATION
_________________________________________________________
 1.  General
_______
 A.  The APU ignition and start system turns the APU engine to the start speed and supplies the spark for combustion. The APU ignition and start system operates automatically. The APU start system has the starter motor and start relay R5. The APU ignition system has the ignition unit, igniter plug and igniter cable.
 2.  Starter Motor (Fig. 1)
_____________
 A.  The starter motor supplies the initial power to turn the APU engine until the APU engine speed is sufficient to supply good airflow for combustion. The starter motor is installed on the gearbox. The starter motor has an electrical motor, spring-loaded friction clutch, and pawl-engagement mechanism. When the starter motor speed increases, the centrifugal force moves the pawls to engage with the ratchet on the accessory drive shaft. The shock of the engagement is absorbed by the spring-loaded friction clutch. The spring-loaded friction clutch also controls the starting torque. The starting torque uses the current from the battery during the initial phase of the APU start. When the electrical power is removed from the starter motor, the APU engine speed will be greater than the starter motor speed. The ratchet will override the pawls until the starter motor speed decreases sufficiently to permit the spring to retract the pawls.
 3.  Start Relay R5 (Fig. 1)
______________
 A.  The start relay R5 transmits the heavy electrical load during the operation of the starter motor. The start relay R5 is found on a floor beam to the right of the E3-1 electrical shelf. To get to the start relay R5, you must remove the right panel between the forward cargo compartment and the electronics bay.
 4.  Ignition Unit
_____________
 A.  The ignition unit supplies the high voltage current to the igniter cable. The ignition unit has a transformer, vibrator, rectifier, booster coil, and a series of capacitors. The ignition unit is in a hermetically-sealed metal container. The ignition unit is installed on the turbine plenum at approximately the six o'clock position.
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APU Ignition and Starting System Component Location
Figure 1 (Sheet 1)

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