B.  Under normal conditions in flight the standby power switch on the P5 overhead panel should be in the AUTO position (Fig. 2). A means is thereby provided for automatically transferring the ac standby bus from the 115-volt ΦA transfer bus No. 1 to the static inverter and the dc standby bus from 28V dc bus No. 1 to the battery bus through relay R37 (Fig. 3). With the switch in the AUTO position, the auto standby power relay (R37) is energized by the No. 1 dc bus and a ground generated by the ac voltage sensor when the 115-volt A transfer bus No. 1 is energized. When either the dc bus No. 1 or phase A of the No. 1 transfer bus becomes de-energized, relay R37 relaxes, connecting the ac standby bus to the static inverter. In the relaxed position, relay R37 connects the ac inverter output to the 115-volt ac standby bus and the battery bus dc directly to the dc standby bus. The standby power system can also be operated with the standby power switch in the BAT position. This supplies a ground for relay R328, causing it to energize. When energized, relay R328 connects the ac standby bus to the static inverter and the dc standby bus to the battery bus. The standby power switch OFF position provides for de-energizing the system during electrical smoke isolation procedures (Refer to wiring diagram). In the OFF position, the standby power switch energizes the standby power off relay (R356), disconnecting the standby buses. The standby power switch has connections to ground for the coil of the standby power transfer relay (R328) and for the coil of relay R37 (Fig. 5). The standby power off light (L5) also comes on, indicating the loss of power on the standby buses. When the airplane is on the ground, relay R38 is energized, providing a ground path to energize the standby power off relay (R356). With R356 energized and the standby power switch in AUTO or OFF position, the connection between the DC STANDBY BUS and the BATTERY BUS is broken, and the static inverter will not turn on because the turn-on signal path is disabled (Fig. 1).
5B8 
24-54-2 Page 2  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 20/85 

H21738
5B8  Standby Power System Simplified Schematic 
Feb 20/87  Figure 1  24-54-2 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Standby Power System Control Location  505 
24-54-2  Figure 2  Oct 20/84 
Page 4 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

STANDBY POWER SYSTEM - TROUBLE SHOOTING
EFFECTIVITY

NZ  ALL EXCEPT ZK-NAP thru ZK-NAS, ZK-NQC;
NZ-NQC after incorporation of SB 24-1040
DL  ALL EXCEPT N301DL thru N330DL;
ND301DL thru N330DL after incorporation of SB 24-1040
AL  ALL EXCEPT N310AU thru N329AU;
N310AU thru N329AU after incorporation of SB 24-1040
YB  ALL EXCEPT 9H-ABA thru 9H-ABC;
9H-ABA thru 9H-ABC after incorporation of SB 24-1040
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 VOLTAGES 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 BAT switch and GRD PWR switch to ON.

508

Jun 20/86 24-54-2 Page 101
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501 
24-54-2 Page 102  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Oct 20/84 

STANDBY POWER SYSTEM -ADJUSTMENT/TEST
EFFECTIVITY

AL ALL EXCEPT N310AU thru N329AU; N310AU thru N329AU after incorporation of SB 24-1040 DL ALL EXCEPT N301DL thru N330DL; N301DL thru N330DL after incorporation of SB 24-1040 NZ ALL EXCEPT ZK-NAP thru ZK-NAS, ZK-NQC; ZK-NQC after incorporation of SB 24-1040
1.  General

A.  Major components of the standby power system are the static inverter, standby power transfer relays, ac voltage sensor, the standby power switch, and the STANDBY POWER OFF light. The standby power system should be checked after component replacement or after any other maintenance has been performed on the system.
　
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