Repair lead.
Replace.
Repair wiring or
connector.

Adjust pickup outputor replace pickup as required.
Replace.
Replace
Recalibrate governor on
test stand.

Repairor replace coil, leads, wiring or connector.
Repairor replace coil, leads, wiring or connector.
Repair or replace sync coil, wiringor connector.
Adjustpickup output.
EFFECTIVITY:
040-999
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL

A. Controlling(continued)
CHART 1
FAULTISOLATION (SYNCHROPHASER INSTALLATION) (Sheet2 of 2)

Fault  Cause  Remedy 
Rightor leftengine increasesrpmout of sync when the synchrophaser  Pickupor associated wiringon enginewhich increasesOPEN.  Repair OPEN wiring or replacepickup. 
is turnedon. 
Pickupoutputlow.  Adjustpickupoutput. 
Insufficientsynchrophaser  Impropergovernor  Recalibrategovernor. 
range. 
Rightcoil,coillead, associatedwiringor connectorgrounded.  Replacesynccoil, repair wiring,repairor replace connector. 
Systemsynchronizesbut is marginallystable.  Pickuporcoilleads swappedbetweenleft andrightengines.  Correctwiringper wiringdiagram. 
CircuitbreakerTrips.  PowerleadSHORTor defectivecontrolbox.  Removefault -replace controlbox. 

12. SynchrophaserWiringTest
Beforeproceedingwith wiringtest,ensurecontrolboxis unplugged,masterswitchis OFF,and synchrophasercircuitbreakeris pulled.
CAUTION:  DO NOT PLUG IN CONTROL BOX UNTIL WIRING TEST IS SATISFACTORILY COMPLETED. EVEN WITH SWITCH TURNED OFF, THE CONTROL BOX CAN BE SERIOUSLY DAMAGED.
NOTE: If anotheraccessoryusessamecircuitbreaker,disconnectcircuitwhilechecking resistancereadings.
(a)
Whenmeasuringpins in connectorplug,performtestper Chart2 with a highqualityohmmeter.

NOTE: Verifywires D,E,L,and J goto leftengine,andwiresC,G,R,andJ go to rightengine.

(b)
Aftercompletingwiringtest,turn masterswitchON (controlboxstillunplugged),reset synchrophasercircuitbreaker,and performthe followingvoltagecheck: (1.) ConnectvoltmeterbetweenreceptacleB andA. (2.) The voltmeterreadingmustbethe sameas powersupply. (3.) Ensurepolarityof pin B is positiveandpinA is negative.

(c)
Aftercompletionof precedingtests,connectcontrolbox.

(d)
Usean oscilloscopeto checkvoltageoutputof governormagneticpickup.

EFFECTIVITY:
040-999 PAGE7
61-20-00

Jan10/90
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Controlling (continued)
CHART 2
SYNCHROPHASER WIRING TEST

NOTE: Following shutdown, resistancereadingscan be 20% higher during heat soak.
TESTBETWEEN  OHMMETER READING 
RECEPTACLENUMBERS  RESISTANCE IN OHMS 
Pin A to Aircraft Ground  Zero Ohms 
All Other Pins to Aircraft Ground*  OpenCircuit 
Pin C to Pin G  52 to 68 Ohms 
Pin D to Pin E  52 to 68 Ohms 
Pin R to Pin J  Approx.170 Ohms 
Pin L to Pin J  Approx.170 Ohms 
*Besure to have excellent ground connection to bare metal. 

13.SynchrophaserFunctionalTest
(a) In level flight and quiet air, synchronize propellerrpm manually, at normal cruisepower settings.Use decrease rpm motion to bring rpm into synchronization, the effect of
minimizing lost motion in governor control linkage.
system ON and let stabilize a few seconds.
(b)
Turn synchrophaser

is lost.

(c)
Slowly reduce left propeller rpm until synchronization

(d)
TurnsynchrophaserOFF and listen for the audible beatfrequencyof propellers. Recordtotal number of beats for a 20 second time period (or 10 seconds and multiply by 2)

willbe reestablished.
(e)
Turn synchrophaser back ON and slowly decreaseright propeller rpm.Synchronization

is lost.

(f)
Continue decreasing right propeller rpm slowly until synchronization

(g)
Repeatstep(d). Add results withresultsof previous step(d). Total equals synchrophaser system holding rangein rpm.

troubleshoot

NOTE: If holding range has large discrepancies, synchrophaser.
(h)
Ifvariationof more than four or five rpm from specifiedholdingrange is found, check for lost motion in governor controllinkagebefore troubleshooting system.

synchrophaser

(i)
If insignificant drift is found in step (h), discrepancyin steps (c) through (h) is due to moving

rpmcontrol of left engine too quickly and total count will be too high. Repeat step (c), ensuring lever movement is very slow.
　
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