C
FWD
Ignition System Component Location Figure 1 (Sheet 1)
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SEE D
SEE E
ENGINE IGNITION CONTROL MODULE D
FUEL CONTROL SWITCH(4 PLACES)
E
Ignition System Component Location
Figure 1 (Sheet 2)
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////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
B. A power source for the standby ignition is available upon loss of normal electrical power.
C. Igniter plug(s) can only be fired with the fuel control switch in RUN position. With the fuel control switch in CUTOFF position, the ignition system circuit is opened, which prevents the igniter plug from firing.
D. Both or either igniter plug may be selected for operation. Continuous operation of igniter plug(s) may also be selected from the control module.
E. For further information on the engine ignition control system, refer to Engine Ignition Control (AMM 74-31-00/001).
6. Operation (Fig. 2)
_________
RECTIFIER &
INPUT POWER STORAGE
FILTER SUPPLY CAPACITOR TRIGGER CAP EXCITER-TO-IGNITER
IGNITER EXCITER
Ignition System Simplified Schematic Figure 2
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A. Functional Description
(1)
When the engine ignition system is energized, 115 volt, 400 Hz power is supplied to the exciter input through an inductance-type radio noise filter to the primary winding of the power transformer. The alternating current is stepped up in the secondary winding and converted to pulsing dc voltage by a rectifier circuit. High voltage output from the rectifier section is passed to a storage capacitor network. When the charge builds to the breakdown potential, discharge occurs and sufficient current flows through the air-cooled exciter-to-igniter plug cable to the igniter plug.
(2)
A high energy spark is made across the plug gap in the combustion chamber, which ignites the fuel/air mixture for the initial start or continuous ignition. The electrical pulse discharge continues until electrical supply to the ignition exciter is discontinued.
B. Control
(1) The ignition system is controlled by the engine ignition control module (AMM 74-31-00/001).
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A / PW4000 SERIES /
747-400 / ENGINES/FAULT ISOLATION/MAINT MANUAL ////////////////////////
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