Unit vibrates.  Unbalancedarmature
assembly.

Excessiverun-outof
armaturebearings.
Fan damaged or out
of balance.

Generator produces full Voltmeter leads reversed.
voltage, but with reversed
polarity.

Residual magnetism in field polescreateswrongpolarity.

Generator overheats.  Continuous overload or
restricted air inlet.

et2 of 3)
Remedy
Locate andcorrect fault.
Free up brushes.
Replace brush holders.
Replacebrushes. If still loose,replace brush holder assemblies.
Replacebearings.
Replacedrive shaft.
Repairor replace defective parts.
Straightenor replacefan.
Balanceor replace
armatureassembly.

Replace armature bearings.
Rebalance or replace fan.
Connectvoltmeter
correctly.

Flash the field.
Check aircraft electrical
systemforgrounds, etc.
Make correction as
necessary.

EFFECTIVITY:
49924-30-009  PAGE

Jan 10/90

PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. DCGeneration(continued)
2. Fault Isolation
CHART 1
FAULTISOLATION(STARTER-GENERATOR) (Sheet3 of 3)

Fault  Cause  Remedy 
D to E paralleling voltage notwithinlimits.  Insufficientcoolingair.  Checkfor air inlet temperature. 
Air flow obstruction; dirt  Checkductingand generator 
accumulationin generator  air inlet. 
ducting. 
Wrongload applied during testing.  Checktestingprocedure and correct condition. 
Starter generator fails startingtest.  Short circuited or open stator winding.  Replace stator and housing assembly. 
Open circuit in armature.  Replace armature. 

Figure 1 
PAGE 4 24-30-00 Jan 10/90  EFFECTIVITY: 040-999 

PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. DCGeneration (continued)
3. MaintenancePractices
CAUTION: DO NOTEXCEED1000HOURSBETWEENOVERHAULSUNLESSOTHERWISE SPECIFIED.
As a precautionarymeasurebetweenoverhaulperiods,it is recommendedthat the starter
generatorsbe givena periodicinspection. (referto 5-50-00) Normallyit will be necessaryto
removethe startergeneratorfromthe enginefor athoroughinspectionof brushesand
commutator.Suchremovalalso affordsthe opportunityto inspectfor splineor dampenerwear,and
otherdetails.
The instructionscontainedin this manualprovidea guidefor line maintenance,inspection,and
brushreplacementonly. Replacementof brushesat this levelis madepossibleby the useof
instantfilmingbrushes.
NOTE: No specialtools arerequiredto accomplishline maintenanceof the startergenerators.
4. Removalof StarterGenerator
Afterenginecowlinghasbeen removed:
(a)
Disconnectandmarkelectricalwiringat terminalblock.

(b)
Disconnectcoolingair inletand exhausthosesor ducts.

CAUTION: THESTARTERGENERATORMUSTBESUPPORTEDBEFORELOOSENING THE HOLDINGCLAMPAS DAMAGETOTHESPLINEMAYOCCUR.CARE SHOULDALSOBEEXERCISEDINTHATTHEUNITDOESNOTHITTHE LOWERENGINEMOUNTWHENREMOVINGIT FROMTHE ENGINE ACCESSORYCOMPARTMENT.

(c)
Supportstartergeneratorand loosenclampbetweenQADandstartergenerator.

(d)
Removestartergeneratorbyslidingaft andlift outof engineaccessorycompartment.

5. Installationof StarterGenerator
(a)
Installstartergeneratorby lift up andslidingforwardof the engineaccessorycompartment.

(b)
Supportstartergeneratorand tightenclampbetweenQADandstartergenerator.

(c)
Connectcoolingair inletand exhausthosesorducts.

(d)
Connectelectricalwiringat terminalblock.

(e)
Installenginecowling.

EFFECTIVITY:

24-30-00an
Jan 10/90

PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL

A. DC Generation (continued)
Terminal Cover 
Quick-Attach-Detach(QAD) MountingKit  CorrectBrush 
Torsion  Fan 
Damper 
Ring 

V-BandAssembly Exhaust Air Holes
Cross Section of Starter Generator Figure 401
6. Adjustmentsof Starter Generator
The only adjustment necessary to maintain the proper generator output is located on the generator controlunit. A voltage of 28.5 volts must be maintained. All other control adjustmentsare made at time of installation and need not be reset.
Since the starter generator and regulator units are designed for use on a single polarity type electricalsystem, the following listed precautions must be observed when servicing the charging circuits.
CAUTION: FAILURE TO OBSERVE THESE PRECAUTIONS COULD RESULT IN SERIOUS DAMAGETO THE ELECTRICAL EQUIPMENT.
　
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