C.  Procedure
 S 424-008 CAUTION: REMOVE THE ELECTRICAL POWER FROM THE AIRPLANE BEFORE YOU REMOVE
_______ THE GCU. YOU CAN CAUSE DAMAGE TO THE CURRENT TRANSFORMER OR THE GCU IF YOU DO NOT REMOVE THE ELECTRICAL POWER.
 (1)  
Install the GCU (Ref 20-10-07/201)
 S 724-005

 (2)  
Do a test of the GCU (Ref 24-21-81/501).

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737-300/400/500MAINTENANCE MANUAL
 GENERATOR CONTROL UNIT - ADJUSTMENT/TEST
________________________________________
 1.  General
_______
 A.  This procedure contains these tasks:
 (1)  
Test of the Generator Control Unit (GCU).

 (a)  This test is used when the GCU is replaced. If a bad CR910 diode is found do this test when the GCU is replaced.

 (2)
Test of the Generator Control Unit (GCU) blocking diode (CR910).

 (a)  
This test is a scheduled maintenance task. This test is not done when the GCU is replaced.

 1)  If a GCU with a defective CR 910 is found, the main battery must be checked or replaced.

 (b)  
The test using the hand held digital multimeter, checks the function of the CR 910 diode. Voltage is measured across the diode circuit. 1) If a bad GCU is discovered when the multimeter test is

 done, only do the GCU replacement test. The multimeter test does not have to be accomplished. ú
 B.  The GCU is found on the P6 panel.
 TASK 24-21-81-705-001
 2.  Generator Control Unit Test
___________________________
 A.  References
 (1)  
71-00-00/201, Power Plant

 (2)  
49-11-00/201, Auxiliary Power Unit

 B.  
Access

 (1)  
Location Zone
 101 Control Cabin - Left
 102 Control Cabin - Right

 C.  
Do a test of the control circuits for engine No. 1.

 S 865-006
 (1)  Start the No. 1 engine (71-00-00/201).
 (a)  
Move the selector switch on the ac meter to the GEN 1 position.

 (b)  
Make sure the DRIVE or LOW OIL PRESSURE light on the P5-5 panel goes off.

 S 865-005
 (2)  
Momentarily push the ERASE button on the M238 annunciator module (behind the P6).

 (3)  
Set the GEN 1 switch to the OFF position.

 S 225-008

 (4)  
Do a check of the voltage:

 S 865-007
 (a)  Push the RESID VOLTS switch.
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737-300/400/500MAINTENANCE MANUAL
 (b)  Make sure the ac voltmeter reads 10 to 21 volts.
 S 865-026
 (5)  
Set the GEN 1 switch to the ON position.

 S 225-009

 (6)  
Make sure the ac voltmeter reads 115 |5 volts ac.

 NOTE: The control (field) relay is closed when the voltmeter
____
 reads 115 |5 volts.

 S 215-010
 (7)  Make sure these lights are OFF:
 (a)  
No. 1 TRANSFER BUS OFF

 (b)  
No. 2 TRANSFER BUS OFF

 (c)  
No. 1 BUS OFF

 (d)  
No. 1 GEN OFF BUS.

 S 865-027
 (8)  
Set the ELEC 2 switch - HYD PUMP A on the P5 panel to the ON position.

 S 865-028

 (9)  
Set the ELEC 1 switch - HYD PUMP B on the P5 panel to the ON position.

 S 215-048

 (10)
 Make sure that the DRIVE or LOW OIL PRESSURE light on the P5-5 panel does not come on.

 S 225-013

 (11)
 Make sure the frequency is 400 |5 Hz.

 S 215-043

 (12)
 Make sure the FF, LV, HV, and MT lights on the M238 annunciator panel are off.
　
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