FUEL QUANTITY INDICATING SYSTEM TOTAL RESISTANCE - INSPECTION/CHECK
1. General
A. A resistance check of a complete tank fuel quantity indicating subsystem is a useful and quick method of checking overall subsystem integrity and as such is a good preliminary to trouble shooting. A low resistance would indicate presence of a short somewhere in subsystem, wire bundles, VTO unit (if installed), tank unit or compensator unit. A high resistance would indicate an open circuit (broken wire or poor terminal contacts).
B. The resistance check covered in this section does not take the place of a fuel quantity indicator calibration adjustment. If indicator accuracy is in question, refer to 28-41-0 A/T or 28-41-05 A/T.
2. Equipment and Materials
A. System Tester (one of the following)
(1)
Model GTF-2, P/N 361-012-001, Gull Airborne Instruments, Inc., 55 Engineers Road, Smithtown, New York, 11787
(2)
P/N 472090-007, 472090-009, or PSD 40-1, Simmonds Precision Products Inc., Panton Road, Vergennes, Vermont 05491
(3)
Model 8000, Barfield Instrument Corp., Miami, Florida 33142
B. Test Harness - F72731-82
C. Leading Edge Flap Actuator Locks - F80046-36
3. Prepare for Resistance Check
A. Provide electrical power (Ref 24-22-0).
WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT ARE CLEAR OF THE LE AND TE FLAPS AND FLAP DRIVE MECHANISMS BEFORE YOU MOVE THE FLAPS. THE FLAPS CAN CAUSE INJURY TO PERSONS AND DAMAGE TO EQUIPMENT.
B. Extend flaps and install leading edge flap locks (Ref 27-81-0 MP).
WARNING: YOU MUST CAREFULLY DO THE STEPS IN THE TASK BELOW TO INSTALL THE LE FLAP SAFETY LOCKS. THE LE FLAPS CAN MOVE QUICKLY IF YOU DO NOT INSTALL THE SAFETY LOCKS CORRECTLY. THIS CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
C. Defuel applicable tank(s) and drain sump fuel (Ref 28-23-0 MP).
D. Open fuel QTY and EP GRD FUELING circuit breakers on P6 panel and attach DO-NOT-CLOSE tags.
E. Gull Tester, Model GTF-2;
Do the Resistance Check
(1) At the applicable spar location (Fig. 601), disconnect the electrical connector from the bussing plug.
CAUTION: DO NOT CONNECT HARNESS TO CONNECTOR LEADING TO INDICATOR OR DAMAGE TO INDICATOR MAY RESULT.
502
May 01/00 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 28-41-91 Page 601
F95208
Bussing Plug Locations 501
28-41-91 Figure 601 Feb 20/84
Page 602
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(2)
Connect the resistance probes to the EXT RES receptacles on the system test unit.
(3)
Set the DISPLAY SELECT on the test unit to RES.
(4)
Set the RESISTANCE FUNCTION switch to EXT RES.
(5)
Set the power switch to ON.
(6)
Touch the probes to each of these locations and make sure the resistance is more than the applicable minimum value:
LEAD 1 LEAD 2 MINIMUM RESISTANCE
Pin 1 of receptacle Pin 2 of receptacle Pin 3 of receptacle Shield of pin 1 Shield of pin 1 Shield of pin 1 Shield of pin 1 Airplane ground 1 megohm 1 megohm 1 megohm 10 megohm
NOTE: Change the position of the probes if the resistance value is less than the minimum value. If you cannot get a resistance that is more than the minimum value, the circuit is bad.
(7)
Connect the test harness to the bussing plug and the system tester.
NOTE: Do not connect the test harness to the connector that goes to the indicator.
(8)
Set the RESISTANCE FUNCTION knob on the system tester to AB to measure the resistance between pin 1 (COAX, Hi Z) and pin 2 (Tank Unit, Lo Z).
(9)
Make sure the resistance is more than 250 megohms.
(10)
Move the system tester switch to measure the resistance between the subsequent pin numbers or conductors.
(a) Make sure the minimum resistance agrees with the values shown in this table:
(11)
If a resistance value is less than the minimum value, do a check for a short circuit in one of these areas (Ref. 28-41-21/501 or 28-41-02/501):
(a)
The tank unit
1) The wires that connect the tank unit to the FQIS
2) The plug that connects the tank unit to the wire bundle
3) The receptacle that connects the tank unit to the wire bundle.
(b)
The compensator unit 1) The wires that connect the compensator unit to the FQIS 2) The plug that connects the compensator unit to the wire bundle 3) The receptacle that connects the compensator unit to the wire bundle.
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