NOTE: Refer to Table 602 for the AMM procedure reference.
____
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747-400 MAINTENANCE MANUAL
(b)
Do the continuity/resistance checks for the replacement fuel pump. 1) Start with this procedure: Fuel Pump Continuity Check.
(c)
Record the continuity/resistance values for the replacement pump on the 747 Fuel Pump Inspection Data Sheet - Replacement Pump (Figure 603).
~................................................................. | Fuel Pump Removal | Reference | ................................................................... | Boost Pump | AMM 28-22-03/401 | ................................................................... | Override/Jettison Pump | AMM 28-31-01/401 | 2............................................…....................1
Table 602
I. Initial Insulation Resistance Check
S 486-054
(1)
Do this procedure: Calibrate the Quadtech Model 1864 Megohmmeter.
S 766-052
(2)
RESISTANCE CHECK WITH THE FUEL PUMP REMOVED FROM THE AIRPLANE; Do these steps to check the insulation resistance:
(a)
Remove the fuel pump motor/impeller unit(s).
NOTE: Refer to Table 602 for the AMM procedure references.
____
(b) Do this procedure on the removed pumps, within two hours: Final Insulation Resistance Check.
S 766-046
CAUTION:_______DO THE RESISTANCE CHECK AT 10 VDC FIRST. THE FUEL PUMPS ARE IN FLAMMABLE LEAKAGE ZONES. EACH PUMP IS TESTED AT 10 VDC BEFORE IT IS TESTED AT 500 VDC. THE INITIAL 10 VDC CHECK IS TO FIND OUT IF A FUEL PUMP HAS LOW INSULATION RESISTANCE WHICH CAN ARC OR OVERHEAT WHEN A HIGH VOLTAGE IS APPLIED. THE RESULTS OF THE 10 VDC CHECK WILL TELL YOU IF IT IS SAFE TO DO THE 500 VDC CHECK WITH THE FUEL PUMP INSTALLED ON THE AIRPLANE.
(3) RESISTANCE CHECK WITH THE FUEL PUMP INSTALLED ON THE AIRPLANE; Do these steps to check the insulation resistance (initial check):
NOTE: These steps are done at 10 VDC to prevent arcing or
____ overheat in a flammable leakage zone when high voltage is applied to a pump with low insulation resistance.
(a)
Do this procedure: Calibrate the Quadtech Model 1864 Megohmmeter.
(b)
Disconnect the electrical connector from the pump motor/impeller unit.
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WARNING: 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.
(c)
Do these steps to connect the QuadTech Model 1864 megohmmeter for the 10 VDC check: 1) Plug the megohmmeter into a grounded receptacle. 2) Connect the +UNKNOWN probe to the pump connector pin 4
(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) Rotate the multiplier switch until the meter reading is less than 5.
NOTE: The resistance is the meter reading multiplied by
____
multiplier switch setting.
2) 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.
3) Record the resistance measured between pin 4 and pin 1 on the 747 Fuel Pump Inspection Data Sheet (Fig. 602). 4) Set the function switch to the DISCHARGE position.
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