IS THE CIRCUIT OK?

YES SEE SHEET 3 (BLOCK 26)
Starter Motor Does Not Turn Figure 110 (Sheet 2)

56 REPAIR THE CIRCUIT FROM THE START RELAY, R5, TERMINAL A1, TO THE "AUX POWER UNIT START" CIRCUIT BREAKER C798 (WDM 49-31-01).
F11361
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
 49-00-00
 PART NUMBER 305593  ú
 ú  02  Page 139
 ú  Jul 12/01 

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////
A / GTCP85-129 SERIES /
737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 2 (BLOCK 25)

YES
NO

26 EXAMINE THE CIRCUIT FROM
THE START RELAY, R5, TERMINAL
X2, TO GROUND (WDM 49-31-01).

 IS THE CIRCUIT OK?
YES
YES27 DO A CONTINUITY CHECK AT THE APU CONTROL UNIT, M280, CONNECTOR D50B, PINS 30 AND 36 (WDM 49-31-01).
IS THERE AN OPEN CIRCUIT?
NO
NO
28 EXAMINE THE CIRCUITS FROM
THE APU CONTROL UNIT, M280,
CONNECTOR D50B, PINS 36,4, TO
THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245,
PINS C,D (WDM 49-31-01).

ARE THE CIRCUITS OK?
YES
YES
29 DO A CONTINUITY CHECK AT
THE ELECTRONIC SPEED SWITCH,
S634, CONNECTOR D1245,
PINS C AND D (WDM 49-31-01).

IS THERE AN OPEN CIRCUIT?
NO
NO
30 EXAMINE THE CIRCUIT FROM
THE APU CONTROL UNIT, M280,
CONNECTOR D50B, PIN 10, TO THE
APU MASTER SWITCH, S248,
CONNECTOR D4218J, PIN 5
(WDM 49-31-01).

IS THE CIRCUIT OK?
YES
64 REPLACE THE APU CONTROL UNIT, M28O (AMM 49-61-11/401).

IF THE PROBLEM CONTINUES, REPLACE THE APU MASTER SWITCH,S248 (WDM 49-31-01).
Starter Motor Does Not Turn
Figure 110 (Sheet 3)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. APU WITH THE ELECTRONIC SPEED SWITCH ú
 49-00-00
 PART NUMBER 305593  ú ú 02 Page 140 ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A12482
////////////////////////A / GTCP85-129 SERIES /737-300/400/500/ ENGINES /MAINTENANCE MANUAL ////////////////////////
FROM SHEET 2
(BLOCK 4)
YES

YES

5
MOVE THE APU MASTER SWITCH
65 MOVE THE APU MASTER SWITCH TO THE "START" POSITION. TO THE "OFF" POSITION. REPLACE THE STARTER MOTOR,
NOTE: AFTER THE AIR INLET M161 (AMM 49-41-11/401).
DOOR OPENS, THERE WILL
BE 28V DC AT THE POSI-TIVE LEAD ON THE
STARTER MOTOR FOR 90
SECONDS.

DO A CHECK FOR 28V DC AT THE POSITIVE LEAD ON THE STARTER MOTOR (WDM 49-31-01).
IS THERE 28V DC AT THE POSITIVE LEAD?

NO YES

6 MOVE THE APU MASTER SWITCH
TO THE "OFF" POSITION.
CONNECT THE NEGATIVE LEAD
TO THE STARTER MOTOR.

EXAMINE THE CIRCUIT FROMTERMINAL X1 TO TERMINAL X2 OFTHE START RELAY, R5 (WDM 49-31-01).
IS THERE AN OPEN CIRCUIT?

NONO

7 DO A CHECK FOR 28V DC AT
67 REPAIR THE CIRCUIT FROM THE START RELAY, R5, TERMINAL THE START RELAY, R5, TERMINAL A1 (WDM 49-31-01). A1, TO THE "AUX POWER UNIT
 IS THERE 28V DC AT START" CIRCUIT BREAKER C798
TERMINAL A1? (WDM 49-31-01).

YES NO NO
8 MOVE THE APU MASTER SWITCH
31 EXAMINE THE CIRCUIT FROM
TO THE "START" POSITION. THE START RELAY, R5, TERMINAL
X1, TO THE APU CONTROL UNIT,

NOTE: AFTER THE AIR INLET
M280, CONNECTOR D50B, PIN 30
DOOR CLOSES, 28V DC (WDM 49-31-01).
ENERGIZE THE START
IS THE CIRCUIT OK?
RELAY, R5, TO CLOSE FOR
90 SECONDS.

YES MAKE SURE THERE IS 28V DC AT THE START RELAY, R5, SEE SHEET 5 TERMINAL X1 AND TERMINAL A2(BLOCK 32) (WDM 49-31-01). IS THERE 28V DC AT TERMINAL X1?

YES SEE SHEET 6
(BLOCK 9)

Starter Motor Does Not Turn
Figure 110 (Sheet 4)

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