(ground). 3) Connect the -UNKNOWN probe to the pump connector pin 1. 4) Set the multiplier dial to the lowest range (100K). 5) Set the TEST VOLTAGE switches to 10V. 6) Set the measure switch to the MEASURE position.
(d)
Do these steps to measure the resistance at the pump:
1) Turn the multiplier switch until the meter reading is less than 5.
NOTE: The resistance is the meter reading multiplied by
____ the multiplier switch setting.
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747-400 MAINTENANCE MANUAL
2) Measure the resistance between pin 4 and pin 1 on the fuel pump electrical connector (Fig. 402, 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.
3) Record the resistance measured between pin 4 and pin 1 on
the 747 Fuel Pump Inspection Data Sheet (Fig. 403). 4) Set the function switch to the DISCHARGE position. 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 override/jettison pump motor/impeller unit. b) Do the continuity/resistance checks again for the
replacement fuel pump. c) Start with this procedure: Fuel Pump Continuity Check.
I. Final Insulation Resistance Check
S 764-200
WARNING: MAKE SURE A QUADTECH MODEL 1864 (OR EQUIVALENT) MEGOHMMETER IS
_______ USED. 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
S 764-201
(2)
Do these steps to measure the resistance at the pump:
(a)
Turn 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. 402, 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. 403).
(d)
Set the function switch to the DISCHARGE position.
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