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1. Descriptionand Operation of Starter Generator System
The starter generator is located on the upper part of the engine accessory section. The purpose of the unit is to provide torque for engine starting and to generate dc electrical power. When this unit is being utilized as a starter, it may be energized byaircraft battery or through the use of an externalpowersourcefor first engine start. Also incorporated is a cross start system to provide generatedpowerto assist the battery in starting the second engine. The cross start relays connect the functioning generatorto the battery and the start solenoid to start the second engine, bypassingthemain bus breakers. Forcross starting, these conditions must be met: operating engine generator switchon, engine at high idle, and second engine start switch to START position.
When the unit is being utilized as a generator, it will provide rated dc output when operated at rated speeds. This generated electrical power is then utilized as required to operate the various electrical systemsof the aircraft.
This unit incorporatesits own cooling system which consistsof an air inlet duct, exhaust duct, and a four bladed fan which is part of the unit. Cooling is obtained by routing the outside ram air throughthe air inlet duct which is then driven through the unit by the four bladed fan and overboard throughthe exhaust duct.
Each unit is controlled by its own independent three position switch: DN for START, UP for GENERATOR,center position OFF. The switches are located on the overhead switch panel (refer to Figure 1). With the battery master switch on, placing the right or left starter generator switch in the START position closes the appropriate starter solenoid for the particular engine. Power is then supplied through the master contactor to the field windings and the armature windings of the starterunit creating a strong magnetic field. The magnetic field now existing in the armature combines with that existing in the field windings of the starter unit driving the armature as required to start the engine.
When the switch is placed in the GEN position, the unit provides rated dc output to the aircraft electricalsystemthrough the voltage control panel and the overvoltage control. Placing the switch in the center or OFF position disconnects the unit from the electrical system of the aircraft.
NOTE: Refer to PA-42-720 (Advanced Trainer) Wiring Diagram Manual, P/N 761 853, for the electrical schematics applicable to these aircraft.
EFFECTIVITY:

24-30-00 Jan
Jan 10/901

PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. DCGeneration (continued)
2. Fault Isolation
Afterthe malfunctioningsystemor componenthasbeen repairedor adjusted,it isrecommended thatthe entiresystembe inspectedfor securityandoperationof itscomponents.Thewiring diagrammanualprovideselectricalschematicsto beusedalongwith conventionaltroubleshooting
methods.
CHART 1 FAULT ISOLATION (STARTER -GENERATOR)
Fault
Unitfailsto operateor does notattainnormalspeed.
Excessivesparkingat brushes.
PAGE2
Jan10/9024-30-00

Cause

Lowvoltagepowersource.
Defectiveswitchin power supply Defectivestartersolenoid.
Damagedarmature.
Shortcircuitedor open statorwindings.
Improperlyseated brushes.
Eccentriccommutator.
Shortcircuitedor grounded fieldwindings.
Excessiveclearancein
bearingsor rough
bearingraces.
Eccentriccommutator.
Shortcircuitin armature
windings.
Brushesincorrectly
installedwithtop
bevelreversed.
Armatureout of balance.
Insufficientbrushrun-in;
improperseating.
(Sheet1of 3)
Remedy
Checkthe powersourceto makecertainthat full voltage is beingappliedto the starter terminals.
Replaceswitch.
Replacesolenoid.
Replacethe armature
assembly.
Replacethe statorand
housingassembly.
Checkbrushseatsand
increasebrushrun-intime.
Refinishcommutator.
Replacestatorandhousing
assembly.
Replacebearings.
Refinishcommutator.
Replacearmatureassembly.
Reverseand reset
Balanceor replace
armature.
Runin brushesuntil
seated.
EFFECTIVITY:
040-999
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL

A. DC Generation (continued)
2. Fault Isolation
CHART 1 FAULTISOLATION (STARTER -GENERATOR) (She
Fault  Cause
Excessive sparking at  Severe overload or short
brushes. (continued)  circuit in aircraft electrical
system.

Brushes sticking in holders.
Weak brush springs.
Brushes loose in holder.

Noisy operation.  Rough bearings.
Scored or worn drive
splines.
Armature rubbing in stator.
　
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本文鏈接地址：夏延飛機維護手冊 Cheyenne IIIA PA-42-720 AMM 1(71)