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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL
5) Do these steps again to measure the resistance between pin 4 and the remaining pins on the fuel pump connector, pins 2 and 3.
(e) Do an analysis of the test results:
1) If each resistance measured between pin 4 and pins 1, 2 and 3 is equal to or more than 1 megohm, do this procedure: Final Insulation Resistance Check.
2) If any resistance measured between pin 4 and pins 1, 2, and 3 is less than 1 megohm, do these steps: a) Replace the pump motor/impeller unit.
NOTE: See Table 602 for AMM reference.
____
b) Do the continuity/resistance checks again for the
replacement fuel pump. c) Start with this procedure: Fuel Pump Continuity Check. d) Record the continuity/resistance values for the
replacement pump on the 747 Fuel Pump Inspection Data
Sheet - Replacement Pump (Figure 603).
J. Final Insulation Resistance Check
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WARNING: IF THE FUEL PUMP IS INSTALLED ON THE AIRPLANE, MAKE SURE A
_______ QUADTECH MODEL 1864 (OR EQUIVALENT) MEGOHMMETER IS USED TO MEASURE THE INSULATION RESISTANCE. IF NOT, IT IS POSSIBLE THAT AN EXPLOSION OR FIRE CAN OCCUR.
(1)
Do these steps to connect the QuadTech Model 1864 Megohmmeter for the 500 VDC check:
(a)
Calibrate the megohmmeter if it is necessary.
(b)
Plug the megohmmeter into a grounded receptacle.
(c)
Connect the +UNKNOWN probe to the pump connector pin 4 (ground).
(d)
Connect the -UNKNOWN probe to the pump connector pin 1.
(e)
Set the multiplier dial to the lowest range (1M).
(f)
Set the TEST VOLTAGE switches to 500V.
(g)
Set the measure switch to the MEASURE position.
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747-400 MAINTENANCE MANUAL
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(2)
Do these steps to measure the resistance at the pump:
(a)
Rotate the multiplier switch until the meter reading is less than 5.
NOTE: The resistance is the meter reading multiplied by the
____
multiplier switch setting.
(b) Measure the resistance between pin 4 and pin 1 on the fuel pump electrical connector (Fig. 601, View B).
NOTE: If the pump resistance is very high, the megohmmeter
____ value will increase with time. For any resistance over 100 megohms it is not necessary to get the actual resistance value. Stop the measurement once the megohmmeter value is more than 100 megohms. Record the measurement on the data sheet as >100 megohms.
(c)
Record the resistance measured between pin 4 and pin 1 on the 747 Fuel Pump Inspection Data Sheet (Fig. 602).
(d)
Set the function switch to the DISCHARGE position.
(e)
Do these steps again to measure the resistance between pin 4 and the remaining pins on the fuel pump connector, pins 2 and 3.
(f)
Put the power switch to the OFF position and remove the test probes.
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(3)
Do an analysis of the test results:
(a)
If each resistance measured between pin 4 and pins 1, 2 and 3 is equal to or more than 5 megohms, then the fuel pump resistance check is satisfactory. 1) If the insulation check is satisfactory, do these steps:
a) If the motor/impeller unit was removed for the test, re-install the motor/impeller unit.
NOTE: Refer to Table 602 for the applicable AMM
____ reference procedure.
b) If the motor/impeller unit was not removed for the test, connect the electrical connector for the motor/impeller unit.
(b) If any resistance measured between pin 4 and pins 1, 2, and 3 is below 1 megohm, do these steps: 1) Replace the motor/impeller unit.
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