S 864-025-N00
 (15) For the applicable engine, remove the DO-NOT-CLOSE tags and close these circuit breakers:
 (a)  P6 Main Power Distribution Panel
 1) 6H19 PROBE HEAT ENG 1
 2) 6H21 PROBE HEAT ENG 2
 3) 6H23 PROBE HEAT ENG 3
 4) 6H25 PROBE HEAT ENG 4

 S 864-019-N00
 (16) Remove the electrical power (AMM 24-22-00/201).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
EXHAUST GAS TEMPERATURE INDICATING SYSTEM - DESCRIPTION AND OPERATION
_____________________________________________________________________
 1.  General
_______
 A.  The indicating system for the exhaust gas temperature (EGT) includes four EGT (TT4.95) thermocouple probes, two EGT (TT4.95) thermocouple cables, a terminal box for the EGT (TT4.95) thermocouple cable, and two housings for the EGT (TT4.95) thermocouple.
 B.  The EGT indicating system monitors exhaust gas temperature sensed at the turbine exhaust case.
 C.  EGT indication is shown on the main EICAS display.
 2.  EGT (TT4.95) Thermocouple Probe (Fig. 1)
_______________________________
 A.  The EGT probes supply two electrical signals to the EEC representative of the gas temperature after it exits the turbine at engine station 4.95.
 B.  There are four EGT probes installed (radially) in the turbine exhaust case at the 1, 4, 7, and 10 o'clock positions. The EGT probes at the 1 and 7 o'clock positions are installed in housings, while the EGT probes at the 4 and 10 o'clock positons are installed in combination average pressure and temperature housings (EPR probes).
 C.  Each EGT probe has six alumel-chromel thermocouples, three for channel A and three for channel B, which are found at three different engine radial positions. A channel A thermocouple is paired with a channel B thermocouple at each position and connected to a pair of chromel and alumel studs in the head of the EGT probe to supply an averaged signal for each channel.
 3.  EGT (TT4.95) Thermocouple Cable (Fig. 1)
_______________________________
 A.  The EGT (TT4.95) thermocouple cable includes a right and left harness assembly which connect EGT (TT4.95) thermocouple probes at the 1, 4, 7, and 10 o'clock positions to the terminal box for the EGT (TT4.95) thermocouple cable at the 5 o'clock position on the turbine exhaust case.
 B.  Each flexible harness assembly includes a stainless steel overbraid for abrasion protection and a copper alloy braid to protect the EEC from electromagnetic interference (EMI) and lightning.
 C.  The wires in each cable includes insulated chromel and alumel wires terminated in chromel and alumel lugs which are attached to the harness wire by fusion welding.
 4.  Terminal Box for the EGT (TT4.95) Thermocouple Cable (Fig. 1)
____________________________________________________
 A.  The terminal box for the EGT (TT4.95) thermocouple cable, found on the turbine exhaust case at the 5 o'clock position, interconnects the EGT (TT4.95) thermocouple cables in parallel to supply two electrically averaged EGT signals (channel A and channel B) to the EEC.
 5.  Indication of the Exhaust Gas Temperature (Fig. 2)
_________________________________________
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
SEE  B 
SEE  FLANGE S FLANGE T A  FLANGE P  FLANGE P  FLANGE T FLANGE S 
CSEE (4 LOCATIONS) PROBE THERMOCOUPLE EGT (TT4.95) 
THERMOCOUPLE CABLE RIGHT HALF OF THE EGT (TT4.95) 
CASE EXHAUST TURBINE 
CASE EXHAUST TURBINE  THERMOCOUPLE CABLE THE EGT (TT4.95) LEFT HALF OF 

TERMINAL BOX FOR THE EGT (TT4.95) THERMOCOUPLE
FWDA  B FWD
CABLE
SEE D
Exhaust Gas Temperature Indicating System - Component Location Figure 1 (Sheet 1)
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