34-31-00
ú ú 08B Page 28 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(7) VOR/ILS Antenna and Transfer Switching Schematic (Fig. 10)
(a)
Figure 10 shows the HSI VOR/ILS-NAV data source annunciators control circuits; the VHF NAV transfer switching control circuits; the HSI transfer switching control circuits; the rf inputs to the navigation units and the antenna switching control circuits.
(b)
HSI Data Annunciators Control Circuits
1) The HSI VOR/ILS or NAV and 1 or 2 navigation data source annunciator control circuits are shown on sheet 1 of Fig. 10. The annunciations are controlled by switched grounds through the VOR/ILS-NAV and VHF NAV transfer relays.
2) The HSI nav source annunciators will display VOR/ILS when the VOR/ILS-NAV transfer relays are in the VOR/ILS position and NAV when the relays are in the NAV position or when electrical power to the HSI is off.
3) The HSI system number annunciators display "1" when electrical power to the HSI is off, when the VOR/ILS - NAV transfer circuits are in the NAV position, or when the VHF NAV transfer circuits are in the BOTH ON 1 position. When the VOR/ILS - NAV transfer circuits are in VOR/ILS position and the VHF NAV transfer circuits are in the NORMAL position, the captain's HSI system number annunciator displays "1" while the first officer's displays "2". Both HSI's display "2" when the VOR/ILS - NAV transfer circuits are in VOR/ILS position and the VHF NAV transfer circuits are in the BOTH ON 2 position.
(c)
VHF NAV Transfer Switching
1) When the VHF NAV transfer switch is in the NORMAL position, the captain is on system No. 1 and the first officer is on system No. 2. Placing the VHF NAV transfer switch to BOTH ON 2 position provides 28 volts dc through the VHF NAV transfer switch and normal contacts of transfer relay No. 2 to transfer relay No. 1. This momentarily energizes transfer relay No. 1 and the relay steps to the BOTH ON 2 position. Positioning the VHF NAV transfer switch back to the NORMAL position, again momentarily energizes transfer relay No. 1 and the relay steps back to the normal position. The first officer's transfer relay is controlled in the same manner as the captain's by positioning the VHF NAV transfer switch to BOTH ON 1.
(d)
HSI Transfer Switching
1) The HSI transfer switching circuits consist of two stepping-type relays and associated HSI transfer switches as shown on sheet 2 of Fig. 10. The circuits control whether the FMCS (AMM 34-62-00) or the selected VOR/ILS navigation system is driving the HSI course navigational displays.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT EFIS ú
34-31-00
ú ú 03B Page 29 ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(e) Antenna Circuits
1) During VOR operation the fin tip VOR/LOC antenna supplies rf through the ILS relays to the navigation units. The nose radome localizer antenna is selected through the ILS relays by mode logic in the DFCS flight computers when making an ILS approach. The logic requires that an ILS frequency be tuned; DFCS approach or VOR/LOC mode must be selected; and the VOR/ILS test inhibit relays in the flight instrument accessory unit energized. The glide slope antenna elements are connected directly to the navigation units.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT EFIS ú
34-31-00
ú ú 08B Page 30 ú Feb 25/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500
MAINTENANCE MANUAL
R44 VHF NAV XFR RLY-1 (E3-4)
R45 VHF NAV XFR RLY-2 (E3-4)
(FIG. 6)
D41 31 VOR/ILS-NAV
ANNUN
34 DATA SOURCE
2 ANNUN
N8 CAPT'S HSI (P1)
(FIG. 6)
D45 31 VOR/ILS-NAV
ANNUN
34 DATA SOURCE
2 ANNUN
HSI VOR/ILS-NAV DATA SOURCE ANNUNCIATORS CONTROL
VOR/ILS Antenna, HSI Data Source Annunciation and Transfer Switching Schematic
Figure 10 (Sheet 1)
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