(n)  
Continue with the instructions shown on the CDU for a check of the FCC-C control of SRM-L and SRM-R.

 (o)  
Push the captain's or first officer's autopilot disconnect switch two times.

 (p)  
Make sure that the STAB TRIM test is completed with no failure.

 G. Put the Airplane Back to Its Usual Condition
 S 865-158
 (1)
Remove electrical power if it is not necessary (Ref 24-22-00/201).

 (2)
Remove hydraulic power if it is not necessary (Ref 29-11-00/201).

 S 865-437
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747-400 MAINTENANCE MANUAL
 AUTOPILOT/FLIGHT DIRECTOR SYSTEM POWER -
________________________________________ DESCRIPTION AND OPERATION
_________________________
 1.  General_______
 A.  The electrical power system operates in the following manner:
 (1)  
Four integrated drive generators (IDG's), each driven by an engine, provide 115/200 volts, 400 Hz, 3 phase ac power. These engine-driven generators are automatically synchronized so that they can be connected to a common synchronous bus to distribute load and provide back-up power for all ac buses.

 (2)  
Transformer-rectifier (TR) units provide 28v dc power by converting 115v ac to 28v dc.

 (3)  
Two generators, each driven by an auxiliary power unit (APU), provide non-parallel 115/200 volts, 400 Hz, 3 phase ac power for all servicing and loading operations of the airplane.

 (4)  
External power is also available through two receptacles which provide non-parallel 115 volts, 400 Hz, 3 phase ac power to the electrical system.

 B.  Power for the Autopilot/Flight Director System (AFDS) is provided by the engine or APU-driven generators via four ac buses. Four TR units provide dc power to four dc buses respectively. Bus No. 4 is backup power for No. 1, 2 or 3 during autoland operation. Power distribution for the AFDS is organized around the three channel configuration of the flight control computers (FCC's), the dual configuration in the AFCS mode control panel (MCP), and the dual requirements of AFDS warning logic.
 2.  Operation_________
 A.  Electrical Power Distribution (Fig. 1)
 (1)  
AC Power

 (a)  Output from each integrated drive generator (IDG) is sent to its respective ac load bus. The load buses may also be powered from other sources through the synchronized bus and bus tie breaker (BTB). A split system breaker (SSB) prevents the paralleling of APU or external power.

 (2)  
DC Power

 (a)  The transformer/rectifier (TR) units convert 115v ac to 28v dc power. Under normal conditions, each TR unit provides dc power to its respective dc bus. During the autoland sequence, the dc buses can be isolated or paralleled by means of the dc isolation relays (DCIR's). DC bus No. 3 normally supplies power to the main battery bus and APU battery bus.
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747-400
MAINTENANCE MANUAL

EXT

EXT
PWR
PWR

APB - AUXILIARY POWER BREAKER GSSR - GROUND SERVICE SELECTOR RELAY BTB - BUS TIE BREAKER IDG - INTEGRATED DRIVE GENERATOR DCIR - DC ISOLATION RELAY SSB - SPLIT SYSTEM BREAKER
GCB - GENERATOR CIRCUIT BREAKER TR - TRANSFORMER/RECTIFIER GHR - GROUND HANDLING RELAYXPC - EXTERNAL POWER CONTACTOR
Electrical Power Distribution
Figure 1

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