REMOVE THE COMBUSTOR UNIT (AMM 49-31-42/401). EXAMINE THE COMBUSTOR FOR TOO MUCH CARBON. DOES THE COMBUSTOR UNIT HAVE TOO MUCH CARBON?

NO
SEE SHEET 2
(BLOCK 3)

APU Engine Has an Explosive PUFF, BANG or Flame During an APU Start
Figure 116 (Sheet 1)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
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FROM SHEET 1 (BLOCK 2)

NO NO NO
3 DO A TEST FOR THE OPENING
23 ADJUST THE OPENING PRES-PRESSURE OF THE ACCELERATION SURE FOR THE ACCELERATION
LIMITER VALVE (AMM 49-11-00/ LIMITER VALVE
501).(AMM 49-11-00/501).
IS THE OPENING PRESSURE ____ IF THE OPENING PRESSURENOTE:OK?
CANNOT BE ADJUSTED, YES
REPLACE THE FUEL CON-TROL UNIT (AMM 49-31-11/401).
START AND OPERATE THE APU
(AMM 49-11-00/201).
DOES THE PROBLEM CONTINUE?
YES
YES

4 DO AN INSPECTION OF THE

FUEL DRAIN ON THE APU
(AMM 49-31-71//601).
IS THE FUEL DRAIN CLOGGED?

NO
YES

5 EXAMINE THE APU SHROUD

DRAINS.
ARE THE APU SHROUD DRAINS CLOGGED?

NO
YES

6 REMOVE CONNECTOR D1264
FROM THE FUEL SOLENOID VALVE.
DISCONNECT THE FUEL LINE

TO THE FUEL ATOMIZER FROM THEFUEL SOLENOID VALVE.
DO THE APU DRY MOTORING(AMM 49-11-00/201).
 DID FUEL FLOW FROM THE FUEL SOLENOID VALVE?

APU Engine Has an Explosive PUFF, BANG or Flame During an APU Start
Figure 116 (Sheet 2)

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A13879
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
"APU GEN OFF BUS"  PREREQUISITES 
LIGHT DOES NOT COME  MAKE SURE THIS SYSTEM WILL OPERATE: 
ON WHEN THE APU  APU (AMM 49-11-00/201) 
ENGINE SPEED GETS  MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION: 
TO 95%  ELECTRICAL POWER IS ON (AMM 24-22-00/201) 

POSSIBLE CAUSES:
1.
APU CONTROL UNIT, M280, PROBLEM (AMM 49-61-11/401)

2.
ELECTRONIC SPEED SWITCH, S634, PROBLEM (AMM 49-61-22/401)

3.
TACHOMETER GENERATOR PROBLEM (AMM 49-61-61/401)

4.
P5-4 MODULE FOR THE APU AND AC SYSTEM GENERATOR PROBLEM.

FAULT ISOLATION:
NO

1 START THE APU
(AMM 49-11-00/201).
PRESS THE LENS OF THE "APU
GEN OFF BUS" LIGHT ON THE P5

21 DO THE APU USUAL SHUTDOWN
(AMM 49-11-00/201).
REPLACE THE BULBS.
DOES THE PROBLEM CONTINUE?
NO

FORWARD OVERHEAD PANEL.
YESDID THE LIGHT COME ON?
YES NO

2 MOVE THE APU MASTER SWITCH

TO THE "OFF" POSITION.
MEASURE THE RESISTANCE AT THE TACHOMETER GENERATOR,CONNECTOR D1262, FROM PIN A TO PIN B (WDM 49-41-01).
IS THE RESISTANCE 15-35 OHMS?

YES NO

3 MEASURE THE RESISTANCE AT
THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245, FROM
PINS C TO D, J TO M, K TO L

52 REPLACE THE P5-4 MODULE FOR THE APU AND AC SYSTEM GENERATOR (WDM 24-27-11; 49-41-01).
(WDM 49-31-01). ARE THE RESISTANCES 0-1 OHMS (MAXIMUM)?

YES
SEE SHEET 2 (BLOCK 4)
APU GEN OFF BUS Light Does Not Come on When the APU Engine Speed Gets to 95%
Figure 117 (Sheet 1)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A14015
FROM SHEET 1 (BLOCK 3)

YES
NO
4 MEASURE THE RESISTANCE AT THE ELECTRONIC SPEED SWITCH,
　
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