YES

NO
2
MAKE SURE THE APU MASTER
SWITCH IS IN THE "OFF"
POSITION.

DISCONNECT THE NEGATIVE LEAD FROM THE STARTER MOTOR. MOVE THE APU MASTER SWITCH TO THE "START" POSITION.
____ AFTER THE AIR INLET
NOTE: DOOR OPENS, THERE WILL BE 28V DC AT THE POSITIVE LEAD ON THE STARTER MOTOR FOR 90 SECONDS.
DO A CHECK OF THE VOLTAGE AT THE POSITIVE LEAD ON THE STARTER MOTOR, M161 (WDM 49-31-01).
IS THERE MORE THAN 8V DC AT THE POSITIVE TERMINAL?

54 MOVE THE APU MASTER SWITCH TO THE "OFF" POSITION. CONNECT THE NEGATIVE LEAD TO THE STARTER MOTOR, M161. REPLACE THE APU BATTERY (AMM 24-31-11/201).
YES
YES

3 MOVE THE APU MASTER SWITCH
TO THE "OFF" POSITION.
 CONNECT THE NEGATIVE LEAD
TO THE STARTER MOTOR, M161.
MANUALLY TURN THE APU
(AMM 49-21-00/201).

ARE THERE UNUSUAL NOISES WHEN THE APU TURNS OR DOES THEAPU NOT TURN AS USUAL?

Starter Motor Turns Slowly
Figure 111 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
STARTER MOTOR
PREREQUISITES
TURNS BUT THE APU
MAKE SURE THIS SYSTEM WILL OPERATE:
ENGINE TURNS SLOWLY
APU (AMM 49-11-00/201)
OR DOES NOT TURN

POSSIBLE CAUSES:
1.
STARTER MOTOR, M161, PROBLEM (AMM 49-41-11/401)

2.
APU INTERNAL DAMAGE (AMM 49-11-00/401).

FAULT ISOLATION:
YES

1 START THE APU
(AMM 49-11-00/201).
 DID THE APU START COR-RECTLY?

MANUALLY TURN THE APU.(AMM 49-21-00/201).
 ARE THERE UNUSUAL APU NOISES WHEN THE APU TURNS OR DOES THE APU NOT TURN AS USUAL?

Starter Motor Turns but the APU
Engine Turns Slowly or Does Not Turn
Figure 112

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
STARTER MOTOR TURNS  PREREQUISITES 
THE APU ENGINE BUT  MAKE SURE THIS SYSTEM WILL OPERATE: 
THERE IS NO COMBUS- APU (AMM 49-11-00/201) 
TION (NO INCREASE  MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION: 
IN EGT)  ELECTRICAL POWER IS ON (AMM 24-22-00/201) 

POSSIBLE CAUSES:
1.
IGNITION SYSTEM: . IGNITER PLUG PROBLEM (AMM 49-41-51/401) . IGNITION UNIT PROBLEM (AMM 49-41-31/401) . IGNITER CABLE PROBLEM.

2.
FUEL SYSTEM: . APU FUEL VALVE, V43, PROBLEM (AMM 28-22-31/401) . FUEL TUBE DAMAGE OR LEAKAGE . FUEL SOLENOID VALVE PROBLEM (AMM 49-31-31/401) . FUEL CONTROL UNIT PROBLEM (AMM 49-31-11/401) . CLOGGED FILTER FOR THE LOW-PRESSURE FUEL (AMM 49-31-21/401) . CLOGGED FILTER FOR THE HIGH-PRESSURE FUEL (AMM 49-31-81/301) . COMBUSTOR UNIT PROBLEM (AMM 49-31-42/401).

3.
OIL PUMP PROBLEM (AMM 49-91-11/401)

4.
THE SEQUENCING SWITCH FOR THE OIL PRESSURE PROBLEM (AMM 49-61-41/401)

5.
ELECTRONIC SPEED SWITCH, S634, PROBLEM (AMM 49-61-22/401)

6.
APU CONTROL UNIT, M280, PROBLEM (AMM 49-61-11/401).

FAULT ISOLATION:
YES SEE SHEET 5

1 DO THE APU DRY MOTORING

(BLOCK 10)
(AMM 49-11-00/201). LISTEN FOR THE NORMAL
SOUND OF THE IGNITION SYSTEM. DO YOU HEAR THE NORMAL SOUND OF THE IGNITION SYSTEM?

NO NO

2 EXAMINE THE IGNITER PLUG
(AMM 49-41-51/601).
IS THE IGNITER PLUG IN
GOOD CONDITION?

YES SEE SHEET 2
(BLOCK 3)

Starter Motor Turns the APU Engine but There Is No Combustion (No Increase in EGT)
Figure 113 (Sheet 1)

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