L. Release GROUND SENSING TEST switch and check that:
(1)
STANDBY PWR OFF light illuminates.

(2)
AC and DC voltmeters read zero.

M. Set STANDBY POWER switch to BAT and check that STANDBY PWR OFF light extinguishes.
N. Set STANDBY POWER switch to AUTO and check that STANDBY PWR OFF light illuminates.
O. Set DC meter selector switch to TR3 and check that DC voltmeter reads zero.
P. Return standby power system to normal.
(1)
Remove electrical power if no longer required (Ref. 24-22-0).

(2)
Set BATT switch to OFF.

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STANDBY POWER SYSTEM - DESCRIPTION AND OPERATION
EFFECTIVITY

ZD G-BKHE thru G-BKHF before incorporating SB 24-1040 WT 5N-AUA thru 5N-AUB before incorporating SB 24-1040 IX N670MA thru M673MA before incorporating SB 24-1040 CA B2504 thru B2505 before incorporating SB 24-1040, B2510
1.  General (Fig. 1)

A.  The ac standby power system is a single-phase, 400-Hz, 115-volt ac power source, which is used to supply power to essential ac systems. The power is used for essential communication and navigation equipment, so that the pilot's essential flight instruments will not be deactivated in the event all 400-Hz generated power becomes unavailable during flight. Under normal conditions, the standby power switch is in the AUTO position and the standby ac bus is energized from the 115-volt ΦA transfer bus No. 1. In the event of losing ac or dc normal power, the ac standby bus is energized from the static inverter.
2.  Operation (Fig. 1)

A.  Power to the ac standby power bus is received from 115 vac transfer bus No. 1 through energized relay R37 and relaxed relay R328. Relay R37 receives power from 28 v-dc bus No. 1 and is grounded through transistor Q1 and standby power switch in AUTO position. Transistor Q1 is biased to ground when the voltage of 115 vac transfer bus No. 1 is 100 v or more.
B.  When the dc bus No. 1 loses power or the 115 vac transfer bus No. 1 voltage is less than 100 vac, Q1 is unbiased, R37 relaxes and connects the inverter output through normally closed contacts in R37 and R38 to the 115-volt ac standby bus.
C.  With the STANDBY POWER switch the BAT position, R328 is energized by the hot battery bus and connects the inverter output to the ac standby bus. 
D.  The standby power off light (L5) comes on when standby power indicator light relay (R330) relaxes, indicating the loss of power on the standby bus.
E.  With the STANDBY POWER switch in the OFF position the system is de-energized.
Jun 20/86 24-54-1 Page 1
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H21727 H34656 H21733
Standby Power System Simplified Schematic  5B8 
24-54-1  Figure 1  Jun 20/86 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

591  Standby Power System Control Location 
Jun 20/83  Figure 2  24-54-1 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Standby Power System Component Location  5B8 
24-54-1  Figure 3  Jun 20/83 
Page 4 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

STANDBY POWER SYSTEM - TROUBLE SHOOTING
EFFECTIVITY

NZ ZK-NQC before incorporating SB 24-1040 CA B2504 thru B2505 before incorporating SB 24-1040, B2510
1.  General

A.  Assume that there are no wiring malfunctions nor more than one problem in the system. If there is more than one malfunction or there are open or shorted wires, further isolation is necessary.
B.  If it is not practical to make the listed checks, replacement of the suspected part(s) may be more efficient for short ground-time maintenance. Refer to wiring diagram 24-34-01  and 24-50-00.
WARNING:  EXERCISE EXTREME CAUTION WHEN WORKING AROUND ENERGIZED PANELS. HIGH VOLTAGE PRESENT CAN BE FATAL.
2.  Prepare for Trouble Shooting
A.  Verify that battery is charged (Ref 24-31-11).
B.  Provide electrical power (Ref 24-22-0).
3.  Standby Power System Trouble Shooting Charts
A.  Place STANDBY POWER switch on P5 panel to BAT.
B.  Open STANDBY POWER AUTO CONT circuit breaker on P6.
C.  Place BAT switch and GRD PWR switch to ON.

508

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5B8 
24-54-1 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Jun 20/83 
　
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