34-31-02

 ú ú 06 Page 34 ú Nov 12/01
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A

737-300/400/500
MAINTENANCE MANUAL

28V DC FROM STBY/HORIZ CB (P18) (34-25-00)
G/S-1 S FLAG (FIG. 13)
G/S-1 DEV
(FIG. 14)

ILS 28V DC (FIG. 13)
LOC-1 DEV (FIG. 14)
S FLAG
+5V LIGHTING (34-25-00)
Standby Attitude/ILS Indicator Schematic
Figure 7

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

 34-31-02
 ú ú 10 Page 35 ú Mar 15/92

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (5)  Radio Digital Distance Magnetic Indicator Schematics (Fig. 8)
 (a)  
A radio digital distance magnetic indicator (RDDMI) is installed on each pilot's instrument panel. Each (RDDMI) displays airplane magnetic heading, VOR bearing, and DME distance.

 (b)  
Heading from the inertial reference system is used to position the compass card through a servo drive system.

 (c)  
The rotor of synchro transmitter B4 is connected to the RDDMI heading gear train. The stator of B4 provides magnetic heading to the navigation units.

 (d)  
VOR bearing is displayed by pointers in the RDDMI with the compass card taken as reference. The pointers are connected to the synchro rotors and receive 26v ac and VOR bearing through the VOR/ADF switches. The pointer flags are biased out-of-view by the VOR valid signal. The ADF/VOR switches are push-on, push-off type and mechanically actuate arrow symbols that annunciate either ADF or VOR legends, depending on mode of operation. The legends ADF/VOR and the associated arrow are lighted by the instrument panel lighting.

 (e)  
When the VOR/ILS system is tuned to an ILS frequency, the associated VOR bearing pointer is parked at a relative bearing of 90 degrees (3 o'clock position).

 (f)  
DME distance, magnetic heading and bearing pointer warning flags appear within the indicator when the associated displays are invalid.

 (g)  
For additional description, operation, and maintenance instructions applicable to the indicators, refer to 34-28-01, IRS; 34-55-02, DME; and 34-57-01, ADF.

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 34-31-02

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A 737-300/400/500MAINTENANCE MANUAL
 (6)  VOR/ILS Power Distribution Schematic (Fig. 9)
 (a)  
The VOR/ILS navigation systems receive 28 volts dc and 115 volts ac through circuit breakers as shown in Fig. 9. System No. 1 receives power from the battery bus and the standby bus in panel P18 while system No. 2 is fed from electronic bus No. 2 in panel P6.

 (b)  
The 115 volts ac is stepped down to 26 volts by instrument transformers No. 1 and No. 2. This 26 volts ac is fed to the navigation units for VOR operation and to the RDDMIs for bearing pointer and heading synchro excitation.

 (c)  
The 28 volts dc from the VHF NAV-1 or -2 VOR/ILS circuit breakers are fed to the navigation units. The VOR/ILS dc powers the internal power supply, arms the ILS mode relay, and provides the ILS 28V DC mode voltage output.

 (d)  
The VOR/LOC dc is also fed to the VHF NAV control panel and to relays in the accessory unit. 1) The VOR/LOC dc to the control panel arms the auto tuning

 circuits, powers the frequency displays, the AUTO/MANUAL annunciators, the test and agility relays, and the manual frequency display shutter bar.
 2)  The VOR/LOC dc to the accessory unit is used to energize the VOR/ILS test inhibit and agility relays.
J1

18

VOR/ADF-1 (34-28-00) 26V AC

BEARING IN (FIG.12)
26V AC
(FIG.9)
BEARING-1

MAG HDG TO VALID (FIG.13)
VHF NAV UNITS (FIG.12)
23 COMMON (FIG.9)
26V AC 10
(FIG.9)
VOR/ADF-2 BEARING IN (FIG.12)
24 26V AC
(FIG.9)
BEARING-2

+5V VALID (FIG.13)
20

LIGHTING
(34-28-00)
21  26 COMMON (FIG.9)
　
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