S634, CONNECTOR D1245, FROM
PIN G TO PIN H (WDM 49-31-01).
IS THE RESISTANCE 4000-6000 OHMS?

YES
NO
5 MEASURE THE RESISTANCE AT
THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245, FROM
PINS A TO G, M TO F, L TO E,
B TO G (WDM 49-31-01).
ARE THE RESISTANCES A MINIMUM OF 1000K OHMS?
YESYES

6 EXAMINE THE CIRCUIT FROM
THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245, PIN H,

TO THE TACHOMETER GENERATOR,
CONNECTOR D1262, PIN A
(WDM 49-31-01; 49-41-01).

IS THERE A SHORT CIRCUIT?

APU CONTROL UNIT, M280, TO THE P5-4 MODULE FOR THE APU AND AC SYSTEM GENERATOR (WDM 24-27-11; 49-31-01; 49-41-01).
IS THE CIRCUIT OK?
YES

APU GEN OFF BUS Light Does Not Come on When the APU Engine Speed Gets to 95%
Figure 117 (Sheet 2)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
 49-00-00
 PART NUMBER 305593  ú
 ú  02  Page 180A
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
E05916
////////////////////////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 NO

1 START THE APU
21 DO THE APU USUAL SHUTDOWN
(AMM 49-11-00/201). (AMM 49-11-00/201).

PRESS THE LENS OF THE "APU REPLACE THE BULBS.GEN OFF BUS" LIGHT ON THE P5 DOES THE PROBLEM CONTINUE? FORWARD OVERHEAD PANEL.

YES
DID THE LIGHT COME ON?
52 REPLACE THE P5-4 MODULE

YES FOR THE APU AND AC SYSTEM GENERATOR (WDM 24-27-11; 49-41-01).
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 SEE SHEET 2
(BLOCK 3)

APU GEN OFF BUS Light Does Not Come on When the APU Engine Speed Gets to 95%
Figure 117A (Sheet 1)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
 49-00-00
 PART NUMBER 3876259  ú
 ú  02  Page 180B
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 1 (BLOCK 2)

YES

NO
3
MOVE THE APU MASTER SWITCH
TO THE "OFF" POSITION.

 DISCONNECT THE ELECTRICAL CONNECTOR D1245, FROM THE ELECTRONIC SPEED SWITCH, S634.

MEASURE THE RESISTANCE AT THE ELECTRONIC SPEED SWITCH, S634, CONNECTOR D1245, FROM PINS, F TO M, K TO L (WDM 40-31-01).
THE RESISTANCE MUST BE LESS THAN 100 OHMS.
MEASURE THE RESISTANCE ATTHE ELECTRONIC SPEED SWITCH, S634, CONNECTOR D1245, FROM PINS, C TO D, J TO M, L TO E(WDM 49-31-01).
THE RESISTANCE MUST BE MORE THAN 1000K OHMS.
ARE THE RESISTANCES VALUES IN THE RANGE SPECIFIED?

THE ELECTRONIC SPEED SWITCH, YOU FIND.
S634, CONNECTOR D1245, PIN H,
TO THE TACHOMETER GENERATOR,
CONNECTOR D1262, PIN A
(WDM 49-31-01, WDM 49-41-01).

IS THERE A SHORT CIRCUIT?

NO NO

5 EXAMINE THE CIRCUIT FROM
THE ELECTRONIC SPEED SWITCH
(95% SWITCH), S634, THRU THE
APU CONTROL UNIT, M280, TO THE
P5-4 MODULE FOR THE APU AND AC
SYSTEM GENERATOR

YES
(WDM 24-27-11; 49-31-01;
57 CONNECT THE ELECTRICAL 49-41-01). CONNECTOR D1254, TO THE IS THE CIRCUIT OK? ELECTRONIC SPEED SWITCH, S634. REPLACE THE APU CONTROL UNIT, M280 (AMM 49-61-11/401).
　
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