(d)
Read ohmmeter. If resistance recorded is below 10,000 ohms, proceed as follows: If ful1-scale deflection (zero ohms) is recorded and no terminals are in accidental contact, replace harness; if large (but not ful1-scale) deflection is recorded, the presence of carbon or excessive moisture may be indicated. Carbon yields a fairly steady reading. Moisture tends to produce readings which waver or drift after 5 to 50 seconds.
NOTE: False drift may be due to variations in applied voltage. To check for false drift, place ohmmeter terminals in contact with each other for 10 seconds. The readings must not wander from ful1-scale deflection (0 ohms).
(e)
Check harness lead resistance between each conductor and wire braid at terminal strip.
NOTE: No insulation resistance check is necessary on harness leads provided with a teflon coating.
(f)
Repeat step (d).
(g)
If presence of moisture is indicated, remove harness and lead, and bake at 200 to 250°F (93 to 121)°C for 1 hour and recheck. A substantial increase in readings indicates that moisture was cause of original low values.
(h)
Install and connect harness and lead; and again measure insulation resistance between conductors and ground. It must be at least 10,000 ohms.
500
May 15/78 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-31 Page 507
(4) Check circuit for shorts and insulation resistance between conductors.
NOTE: No short circuit check is necessary on harness leads provided with a teflon coating.
(a)
Disconnect one lead from each EGT thermocouple probe.
CAUTION: DO NOT BEND OR TWIST THERMOCOUPLE PROBE TERMINALS, TERMINALS MAY LOOSEN IN SUPPORTING INSULATION, AND THERMOCOUPLE FUSED JUNCTION MAY BREAK.
(b)
Set ohmmeter (sensitive) switch to range with center scale value of approximately 10 ohms.
(c)
Check each individual probe circuit in harness for short circuits at EGT circuit connector receptacle. Refer to figures 501 and 502. 1) Flex harness gently and observe instrument needle. If any deflection results
(unless caused by accidental contact of harness terminals at EGT probes), replace harness.
(d)
Check harness lead for short circuits at terminal strip.
1) Flex harness lead gently and observe needle. If any deflection results, replace lead.
(e)
Check proper operation of ohmmeter (low voltage) by touching test terminals together and noting needle deflection to read zero ohms.
WARNING: TO RESCUE POSSIBILITY OF IGNITING FUEL, DO NOT USE A MEGGER OR OTHER HIGH VOLTAGE OHMMETER.
(f)
Check resistance of insulation between conductors by placing one ohmmeter terminal in contact with EGT connector receptacle pin I and other ohmmeter terminal in contact successively with pins A through H. If resistance is below 10,000 ohms, replace harness.
(g)
Check resistance of insulation between harness lead conductors at terminal strip. If resistance is below 10,000 ohms, replace harness lead.
(h)
Connect leads to EGT probe terminals.
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CAUTION: DO NOT BEND OR TWIST THERMOCOUPLE PROBE TERMINALS AS TERMINALS MAY LOOSEN IN SUPPORTING INSULATION, AND THERMOCOUPLE FUSED JUNCTION MAY BREAK.
(5) Return airplane to normal configuration.
(a)
Slide duct cover ring into the fan discharge turbine exhaust inner rear duct and secure with 12 screws.
(b)
Connect harness lead to terminal strip.
(c)
Connect EGT circuit connector. On engine equipped with a junction box, connect output leads; install bus bar, secure with nuts and install cover.
(d)
Close engine left cowl panel.
(e)
Remove placards in control cabin and close applicable engine circuit breakers.
500
Aug 15/78 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 77-21-31 Page 509
EXHAUST GAS TEMPERATURE HARNESS AND LEAD - CLEANING/PAINTING
1. EGT Harness and Lead Cleaning
A. Equipment and Materials
(1) Solvent - Trichlorethylene
B. Clean Harness and Lead
(1)
Clean external surfaces by wiping with cloth slightly dampened with trichlorethylene solvent.
(2)
If necessary, clean all terminal contact surfaces, using a stainless steel brush or stainless steel pad without soap.
CAUTION: NO FOREIGN MATERIAL SHALL BE LEFT ON TERMINALS. EXHAUST GAS TEMPERATURE INDICATOR - REMOVAL/INSTALLATION
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