(3)
Adjust resistor spool to decrease circuit resistance.
(a)
Disconnect resistance spool wire from terminal B3 with a soldering iron. (See figure 502.)
(b)
Unwind resistance wire from center post. On the basis of approximately 0.7 ohms per foot (.058 ohms per inch) unwind approximate amount of wire necessary to give correct resistance.
(c)
Connect wire near the end to terminal B3 with an alligator type clip.
(d)
Repeat steps (2)(h) through (2)(m).
NOTE: Be sure clip penetrates resistance wire insulation to make a good electrical contact.
Exhaust Gas Temperature Thermocouple Resistor Adjustment 500
77-21-11 Figure 502 (Sheet 1) Aug 15/67
Page 502
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
500 Exhaust Gas Temperature Thermocouple Resistor Adjustment
Aug 15/67 Figure 502 (Sheet 2) 77-21-11
Page 503
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
E. Restore system to normal configuration.
(1)
Disconnect Wheatstone Bridge from indicator plug. Reconnect plug to indicator
receptacle.
(2)
Replace resistor cover and side panel.
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77-21-11 Page 504 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. May 15/68
EXHAUST GAS TEMPERATURE THERMOCOUPLE PROBE - REMOVAL/INSTALLATION
1. Equipment
A. Wrench, Thermocouple Spannernut - PWA-12437 (Pratt & Whitney Aircraft, East Hartford, Conn.)
2. Prepare to Remove Thermocouple Probe section.
B. Observe the following precautions for maintenance in engine exhaust section.
(1)
Pull applicable engine START IGNITION circuit breaker on circuit breaker panel P6-2, and placard the circuit breaker with DO NOT CLOSE.
(2)
Placard thrust reverser controls with DO NOT OPERATE.
WARNING: SERIOUS INJURY CAN OCCUR IF ENGINE IS STARTED AND/OR IF THRUST REVERSER IS OPERATED.
3. Remove Thermocouple Probe
A. Enter engine exhaust section.
B. Remove screws retaining fan exhaust inner rear case. Slide it to rear (Ref Chapter 72).
C. Disconnect alumel and chromel leads from thermocouple probe.
D. Cut lockwire and remove spannernut securing thermocouple probe to turbine rear inner case using wrench.
NOTE: It may be necessary to remove harness supporting clips from turbine rear inner case for locknut removal.
E. Push thermocouple probe through turbine rear inner case into turbine discharge passage, then remove probe through rear of engine.
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4. Install Thermocouple Probe
A. Install thermocouple probe into turbine rear inner case, aligning lug in case with slot in probe.
B. Using PWA33449 wrench, secure thermocouple probe with locknut.
C. Tighten locknut to 450-500 inch pounds and install lockwire.
D. Attach alumel and chromel leads to thermocouple probe and tighten nuts to torque value specified in 72-00 R/I, P&WA JT8D Maintenance Manual.
CAUTION: TORQUE REQUIREMENTS FOR LOCKNUTS ON THERMOCOUPLE LEAD STUDS SHALL BE OBSERVED. OVER TORQUING IF LOCKNUTS CAN RESULT IN STUD LOOSENING OR BREAKAGE.
NOTE: For engines incorporating SB 1957, proper installation of Terminal Nuts (PN 558987 and 558988) requires that cylindrical grooved portion of nut must lead the way onto stud.
E. Slide fan exhaust inner rear case into position and secure with 12 screws and washers. F Exit engine exhaust section.
G. Remove DO NOT OPERATE placard from thrust reverser controls.
H. Remove DO NOT CLOSE placard from applicable engine START circuit breaker and close circuit breaker on panel P6-2.
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EXHAUST GAS TEMPERATURE THERMOCOUPLE PROBE - INSPECTION/CHECK
1. Exhaust Gas Temperature Thermocouple Probe Check
A. Check Exhaust Gas Temperature Thermocouple Probe Visually
NOTE: For EGT thermocouple probe access information, refer to Exhaust Gas Temperature Thermocouple Probe - Removal/Installation.
(1)
Check all surfaces of thermocouple for nicks, cracks, bending or evidence of heat erosion.
(2)
Check probe for straightness. Allowable deformation is 1/8 inch for small OD (lower end) of the probe.
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