PAGE24-30-00
Jan 10/90
PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. DCGeneration (continued)
11. Description and Operation of Generator Control Unit
The generator control unit is designed to incorporate all the normal features of a direct current 28-
volt control system in one compact unit having three printed circuit boards. By using a comparator
amplifier with a regulated reference voltage, any difference between the reference voltage and the
generator output, as seen by the sensing line, is amplified and supplied to the comparator circuit,
which controls the shunt field excitation of the generator.
The paralleling portion of the generator control unit (one on each engine) incorporates the
advantagesprovided by integrated circuitry.The difference betweenthe interpole voltage of the
local generator and interpole of the other generatoris amplified, inverted, and filtered. Any
resultant difference is then coupled to the summing junction of the voltage regulating circuit. The
equalizingcircuit continuously sumsthe difference between the interpole voltages of both
generators to zero.
The line contactor and reverse current control circuitry consists of two integrated circuits and differentialvoltage sensing operations. When the generator has attained an output voltage equal to the tie bus voltage, these circuits allow the line contactor to close. They also monitor the differencein voltage across the interpole terminals of each generator. When this potential reaches a positive voltage of 0.2 volts or more, the integrated circuits, after a time delay inversely proportionalto the magnitude of the voltage, cause the line contactor to open. When this happens, the circuit automaticallyshifts back to differential voltage sensing.
12. Removal of Generator Control Unit
Locationof generator control unit is on the aft engine nacelle electrical accessory panel,aft of
enginefirewall at station 108.50 on respective engine.
(a)
Remove the aft upper engine panel for access to generator control unit.
(b)
Disconnectelectricalplugfrom control unit.
(c)
Remove mounting screws and lift unit from airplane.
13. Installation of Generator Control Units
(a)
Positiongeneratorcontrolunit on aft engine nacelle panel and secure with appropriate screws.
(b)
Reconnect electrical plug.
(c)
Replaceaft engine accesspanel and secure with appropriate screws.
NOTE: The replacement of generator control units require a functional check for proper operation(refer to Checking Generator Control Unit paragraph).
14. CheckingGenerator Control Unit
(a)
Start engines and set to a gas generatorrpm of 60%. Turn on all electrical equipment available in aircraft; systemvoltage must remain at 28 + 1 volts. NOTE: Voltage adjustment screwis located above connector of generator controlunit,
between the two test jacks.
(b)
Turn the left startergeneratorswitchto the OFF position. Thiswilltransferthe full electrical loadto the right generatorand generator controlunit. Systemvoltagemust remain at 28 ± 1 volts.
EFFECTIVITY: 040-999
Jan10/9024-30-00
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. DCGeneration(continued)
14. CheckingGeneratorControlUnit (continued)
(c)
Turnleftstarter generator switchto the ON position and turnthe right startergeneratorswitch off. Thiswill transfer the full electrical loadto the left starter generator and generatorcontrol unit. The system voltage mustremain28 ± 1 volts.
(d)
If the voltage does not remainat 28 ± 1 volts, check the generatorand battery, makingsure
theyare in goodcondition.Checkall circuit connectionsand all wiringin the starter generator systemfor unwanted resistance.Wiring connections shouldbe cleanedand soldered as necessary.Checkvoltmeterfor accuracy and repeattest. If system voltagestillis not within28 ± 1 volts, refer to performance test.
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本文链接地址：夏延飞机维护手册 Cheyenne IIIA PA-42-720 AMM 1(75)
