(c)  
Supply external power to the ground service bus (AMM 24-22-00/201).

 (d)  
Measure 28 |4 volts AC.

 S 865-038
 (15)
 Remove electrical power if it not necessary (AMM 24-22-00/201).

 S 865-039

 (16)
 Remove the meter and close the P34 panel.

 S 445-040

 (17)
 Do the activation procedure for the spoilers (AMM 27-61-00/201) if previously deactivated.

 TASK 24-50-00-715-041
 4. Operational Test - Instrument Bus Voltage Sensing Unit
______________________________________________________
 NOTE: This is a scheduled maintenance task.
____
 A. References
 (1)  
AMM 24-22-00/201, Electrical Power - Control

 (2)  
AMM 27-61-00/201, Spoiler/Speedbrake Control System

 B. Prepare for the Test
 S 045-058
 WARNING: DO THE DEACIVATION PROCEDURE FOR THE SPOILERS OR MOVE ALL
_______ PERSONS AND EQUIPMENT AWAY FROM THE SPOILERS. THE SPOILERS CAN RETRACT QUICKLY AND CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
 (1)  Do the deactivation procedure for the spoilers (AMM 27-61-00/201) or move all persons and equipment away from the spoilers.
 C. Do a Test of the Instrument Bus Voltage Sensing Unit
 S 715-065
 (1)  Do a test of the instrument bus voltage sensing units as follows:
 (a)  Supply external power to the main AC buses (AMM 24-22-00/201).
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757
MAINTENANCE MANUAL

 (b)  
Push the STATUS switch on the EICAS display select panel, P9.

 (c)  
Make sure that EICAS message, CAPT INSTR XFER, does not show on the bottom display.

 (d)  
Open this P6 panel circuit breaker:
 1) 6M16, CAPT PRIM INSTR BUS oA

 (e)  
Make sure the EICAS message, CAPT INSTR XFER, shows on the bottom display.

 (f)  
Close this P6 panel circuit breaker:
 1) 6M16, CAPT PRIM INSTR BUS oA

 (g)  
Make sure the EICAS message, F/O INSTR XFER, does not show on the bottom display.

 (h)  
Open this P6 panel circuit breaker:
 1) 6M22, F/O PRIM INSTR BUS oA

 (i)  
Make sure the EICAS message, F/O INSTR XFER, shows on the bottom display.

 (j)  
Close this P6 panel circuit breaker:
 1) 6M22, F/O PRIM INSTR BUS oA

 D. Put the Airplane Back to Its Usual Condition
 S 445-042
 (1)  
Do the activation procedure for the spoilers if you did the
 deactivation procedure (AMM 27-61-00/201).

 (2)
Remove electrical power if it is not necessary (AMM 24-22-00/201).

 S 865-043
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757 MAINTENANCE MANUAL
 115 - VOLT AC POWER DISTRIBUTION
________________________________ DESCRIPTION AND OPERATION
_________________________
 1.  General_______
 A.  The left main AC bus supplies power to the AC center bus, AC standby bus, captains flight instrument transfer bus, left utility bus, and left galley buses. The right main AC bus supplies power to the ground service bus, right utility bus, first officers flight instrument transfer bus, and right galley buses. The ground handling bus is powered from external power or the APU generator. System components include: Utility bus relays, center bus transfer relay, ground service select relay, ground service transfer relay, ground handling relay, and instrument bus voltage sensing units.
 2.  Component Details (Fig. 1)_________________
 A.  Utility Bus Relays
__________________
 (1)  Utility buses are connected to the main AC buses through utility bus relays. These relays are controlled by the bus power control unit (BPCU), and can be de-energized if load reduction is necessary. Relays are located in P70 misc. electrical equipment panel, and P37 right misc. electrical equipment panel.
　
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