B. A capacitance trim unit is used to adjust the capacitance of the fuel quantity indicating system to a specified value when the tanks are dry. With this adjustment, it is not necessary to calibrate the fuel quantity indicators when you replace an indicator. The capacitance trim unit is a shielded capacitor that you can adjust. It has a range of 2-30 picofarads (pf).
TASK 28-41-86-004-001
2. Capacitance Trim Unit Removal_____________________________
A. Access
(1) Location Zone
101 Control Cabin Left
B. Procedure
S 864-002
(1) Open these circuit breakers and attach DO-NOT-CLOSE tags:
(a) P6 Main Power Distribution Panel
1) QTY
2) EP GND FUELING
S 034-003
(2)
Remove the parts that attach the capacitance trim unit (Fig. 401).
(a)
Find the mounting bracket on the forward left side of the control stand above the pilot's hand microphone receptacle.
(b)
Remove the three screws that attach the capacitance trim unit to the mounting bracket.
(3)
Move the capacitance trim unit away from the control stand.
S 034-005
(4)
Find the splice on the wire bundle that goes from the capacitance trim unit to the airplane.
S 034-006
(5)
Cut the wires at a good position adjacent to the splice.
S 014-004
(a) Make sure there is a sufficient length of the wire to make a new splice.
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A
737-300/400/500MAINTENANCE MANUAL
S 494-007
(6)
Attach a tag to the wires to identify them.
S 024-008
(7)
Remove the capacitance trim unit.
TASK 28-41-86-404-009
3. Capacitance Trim Unit Installation__________________________________
A. References
(1)
SWPM 20-30-12
(2)
28-41-00/501, Fuel Quantity Indicating System
(3)
28-41-02/501, Fuel Quantity Indicating System
B. Access
(1) Location Zone
101 Control Cabin Left
C. Procedure
S 434-010
(1) Connect the wires of the capacitance trim unit to the applicable airplane wires with multiple wire shield splices (SWPM 20-30-12).
NOTE: Use the tags that you attached when you cut the wires.
____
S 424-011
(2)
Put the capacitance trim unit into the side of the control stand panel (Fig. 401).
S 434-012
(3)
Put the mounting bracket of the capacitance trim unit in the correct position.
(4)
Install the mounting screws.
S 864-014
(5)
Close these circuit breakers and remove the DO-NOT-CLOSE tags:
S 434-013
(a) P6 Main Power Distribution Panel
1) QTY
2) EP GND FUELING
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A
737-300/400/500MAINTENANCE MANUAL
S 824-023
(6) Do this task: "System Adjustment - Fuel Quantity Indicating System" (Ref 28-41-00/501, 28-41-02/501).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
FUEL QUANTITY CALIBRATION
TANK 1 CTR TANK TANK 2
CAPACITANCE TRIMMER
SEE B
CONTROL
STAND
SEE A
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