(g)
6G18 SCU ALT PWR ENG 4
(h)
6G26 ENG SCU 4
S 046-024-N00
WARNING: DO THE THRUST REVERSER DEACTIVATION PROCEDURE TO PREVENT THE
_______ OPERATION OF THE THRUST REVERSER. THE ACCIDENTAL OPERATION OF THE THRUST REVERSER CAN CAUSE INJURIES TO PERSONS OR DAMAGE TO EQUIPMENT.
(2)
Do this procedure: Thrust Reverser Deactivation for Ground Maintenance (AMM 78-31-00/201).
(3)
Open the core cowl panels (AMM 71-11-06/201).
S 016-006-N00
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(4) S 036-007-N00Remove the nuts and washers which attach the harness leads for the EGT thermocouple cable to the probe studs at each probe location. (a) Remove the harness leads from the probe studs.
NOTE:____ Tag all thermocouple leads to make sure they are installed correctly. The nut and stud diameters of the alumel terminals are larger than those of the chromel terminals.
(5) S 026-031-N00Disconnect the left and right EGT thermocouple and harness leads from the terminal box studs. (a) Remove the screws which attach the cover, harness ground lead, and inner and outer clamp halves to the terminal box. (b) Remove the cover and clamps from the engine. (c) Remove the nuts which attach the harness leads for the EGT and EEC thermocouple cable to the terminal studs. (d) Disconnect the harness leads.
(6) S 766-025-N00Set the ohmmeter range switch to the range which has the center scale value of approximately 10 ohms.
(7) S 766-008-N00Do a continuity check of each circuit.
NOTE:____ Broken wires, which intermittently touch when they are bent, will cause the needle to move. Incorrect intermittent indications will occur if the ohmmeter prods do not satisfactorily touch with the clean terminals or if the ohmmeter prods, leads, or jacks are defective.
(a) Replace all defective EGT thermocouple cables (AMM 77-21-02/401).
(8) S 766-009-N00With a low voltage ohmmeter, examine the insulation for short circuits, leakage, and internal insulation chafing.
NOTE:____ You must use a low voltage ohmmeter which uses less than 40 volts dc and keeps a tolerance of five percent to find the insulation resistance.
(a) To examine the ohmmeter for correct operation, touch the test prods together and make sure the needle shows zero ohms.
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
(b) Touch one prod with the steel braid covering and the other prod
with the terminal box studs that follow and read the ohmmeter:
1) Alumel, T/C 3 and T/C 4, Circuit A
Alumel, T/C 2 and T/C 1, Circuit A
Chromel, T/C 3 and T/C 4, Circuit A
Chromel, T/C 2 and T/C 1, Circuit A
Alumel, T/C 3 and T/C 4, Circuit B
Alumel, T/C 2 and T/C 1, Circuit B
Chromel, T/C 3 and T/C 4, Circuit B
Chromel, T/C 2 and T/C 1, Circuit B
(c) If there is full scale movement, and no terminals accidentally
touch, replace the EGT thermocouple cable half
(AMM 77-21-02/401).
(d) If there is a large movement, but not a full scale movement, it
is a sign of carbon or moisture.
NOTE: Carbon will show a stable indication while moisture____
will show an indication which will move after 5-30
seconds. The applied voltage will also cause movement
of the needle. To do a check for incorrect indication,
touch the prods with each other for ten seconds. The
needle must not move from the full-scale indication.
(e) If there are signs of moisture, remove the damaged EGT
thermocouple cable (AMM 77-21-02/401).
1) Put the EGT thermocouple cable in a temperature of
220-250°F (104-121°C) for one hour.
2) Do the check again.
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