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A 737-300/400/500MAINTENANCE MANUAL
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EITHER UNDER FREQUENCY OR OVERCURRENTCAUSE A LOW VOLTAGE (LV) LOCKOUT.
Operating Condition TabulationFigure 101
A 737-300/400/500MAINTENANCE MANUAL
THE VSCF TRIPS OFF LINE AND THE "FF" LIGHT ON THE M238 MODULE COMES ON

1

DO THE BIT TEST OF THE VSCF (PUSH THE "INDICATE" BUTTON OR PULL THE BIT SWITCH ON THE THE VSCF TO THE INDICATE POSITION AS APPLICABLE).
DOES THE "VSCF FAULT" LIGHT COME ON?
NO
PREREQUISITES
MAKE SURE THE AIRPLANE IS IN THIS CONFIGURATION: ELECTRICAL POWER IS ON (AMM 24-22-00/201). ENGINES SHUTDOWN
YES
31 REPLACE THE VSCF, G1 (AMM 24-11-11/401), OR DO THE FAULT ISOLATION PROCEDURE "VSCF BIT FAULT LIGHT COMES ON" IN FIG. 103).
NO

32 REPLACE THE GCU, G3 OR G4
(AMM 24-21-81/401). IF THE PROBLEM CONTINUES,YES DO THE STEP IN BLOCK 3.
NO
23 EXAMINE THE POWER FEEDER

33 REPLACE THE GCB1, C801 OR
CABLES BETWEEN TERMINALS T1,T2 GCB2, C802.
AND T3 OF THE VSCF G1 AND IF THE PROBLEM CONTINUES,
TERMINALS B1,B2 AND B3 OF REPLACE THE VSCF.
G-CB1, C801 OR GCB2, C802 FOR OPEN CIRCUITS (WDM 24-21-11, -21).
 DO YOU SEE AN OPEN CIR-CUIT?
YES

34 REPAIR THE DAMAGE TO THE POWER FEEDERS.
YES

3 EXAMINE THE POWER FEEDERCABLES BETWEEN TERMINALS T1,

T2, AND T3 OF THE VSCF G1 AND
TERMINALS B1,B2, AND B3 OF
GENERATOR CIRCUIT BREAKER-1
C801 OR GENERATOR CIRCUIT
BREAKER-2 C802 FOR ARCING
(WDM 24-21-11-21).
DO YOU SEE SIGNS OF ARCING ON THE POWER FEEDERS?

NO
SEE SHEET 2 (BLOCK 4)

The VSCF Trips OFF Line and the "FF" Light on the M238 Module Comes On
Figure 102 (Sheet 1)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
FROM SHEET 1
(BLOCK 3)
NO YES4

EXAMINE THE WIRING BETWEEN
TERMINALS B1,B2, AND B3 OF
GCB1, C801 OR GCB2, C802 AND
THE DISTRIBUTION CIRCUIT
BREAKERS IN THE P6-11 (NO. 1)
OR P6-12 (NO. 2) PANEL FOR
SHORT CIRCUITS (WDM 24-22-31;
24-51-11,-21).

IS THERE A SHORT CIRCUIT?

NO YES YES

5 DISCONNECT THE D26 CONNEC-

24 DISCONNECT THE D30 OR D34
TOR FROM THE BRACKET ON THE CONNECTOR FROM THE LOAD SIDE
NEUTRAL DPCT T1 ON THE ENGINE DPCT T4 OR T5. MEASURE THE
(WDM 24-23-11,-21). RESISTANCE BETWEEN PIN 4 AND

MEASURE THE RESISTANCE EACH OF PINS 1,2, AND 3 ON THE BETWEEN TERMINAL C4 AND EACH LOAD SIDE DPCT T4 OR T5 OF TERMINALS C1,C2, AND C3 ON (WDM 24-23-11,-21). THE VSCF G1. THE RESISTANCE SHOULD BE
THE RESISTANCE SHOULD BE BETWEEN 1 AND 10 OHMS AT ALL BETWEEN 1 AND 10 OHMS AT ALL TERMINALS. TERMINALS. ARE ALL OF THE RESISTANCE
 ARE ALL OF THE RESISTANCEMEASUREMENTS BETWEEN 1 AND MEASUREMENTS BETWEEN 1 AND 10 OHMS? 10 OHMS?
NONO

The VSCF Trips OFF Line and the "FF" Light on the M238 Module Comes On Figure 102 (Sheet 2)
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A

737-300/400/500MAINTENANCE MANUAL 
　
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