737-300 400 500 AMM 飞机维护手册导航 NAVIGATION 2(126)_航空信息_民用航空_通用航空

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b) Modulated rf test signals, generated by the self-test oscillators, are applied to the input of the VHF and UHF receiver sections to simulate a VOR signal on any VOR channel or localizer and glide slope signals on any ILS channel. These signals provide an overall operational test for the VOR/ILS navigation system.
c) Prior to self-test initiation control, logic will allow normal operation of the glide slope and VOR/localizer flags. When self-test is initiated the flags will remain in view for 3 |1 seconds, retract from view and 20 |5 seconds after initiating test, reappear and remain in view for as long as the self-test is actuated.
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A
737-300/400/500MAINTENANCE MANUAL
(2) VHF NAV Control Panel Schematic (Fig. 5)
(a)
The panel provides control of the VHF NAV and DME systems. Switches are provided to select automatic or manual frequency control, select the frequency during manual operation, and initiate self-test of the VHF NAV and DME systems.

(b)
Manual Tuning

1) When relay K1 is relaxed, tuning is performed manually. MAN is annunciated on the AUTO/MAN selector switch. The annunciator is illuminated by 28v dc form J1-46, and the return is through K1 to the airplane master dim circuit. K1 applies the frequency select common to the 2-out-of-5 encoder, enabling the switched output. The manual lines are connected through J1 to the VHF NAV receiver and to the DME interrogator. The manual frequency display is driven from the unswitched output of the encoder, and AUTO is blanked.

1) The auto tune function is armed by 28v dc from J1-48. When the AUTO/MAN switch is pressed, the relay control is set, energizing K1. With K1 energized, AUTO is annunciated and the encoder enable is removed. The auto display is enabled by the display power and the frequency select common, switch by K1. Display power is applied to the bar solenoid and the bar is raised over the manual display. Auto frequency control is provided by the flight management system, which is connected in parallel with the panel output to the VHF NAV receiver and to the DME interrogator. The frequency is displayed by the AUTO display. Auto tuning is deselected by pressing the AUTO/MAN switch, resetting the relay control circuit, or when the auto tune arm discrete is removed from J1-48.

(d)
Agility Tuning

1) The flight management system provides a ground to J1-16, and K2 energizes. As agility tuning occurs only during AUTO, K1 is energized and the frequency select common is applied, through K1 and K2, to the auto display, and dashes are displayed.

(e)
Test Functions

1) When the airplane LIGHTS master dim and test switch on center instrument panel P2 is in TEST position, relay K3 in the VHF NAV control panel is energized. This illumates the AUTO and MAN switch indicators and applies a test discrete to the AUTO and MANUAL frequency displays. The frequency displays test indication is a flashing 188.88, alternating 2 seconds on and 1 second off.
2) VHF NAV tests are enabled by grounds from the test switches. When a VOR, UP/LT, or DN/RT test is initiated, the flight management system interlock is interrupted.
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A 737-300/400/500MAINTENANCE MANUAL

FIG. 9
FIG. 11

FIG. 9
NC
DME AND VHF NAV TUNING (FIG. 11)

FIG. 15

DISPLAY TEST VALUES SHOWN (TWO SECONDS ON, ONE SECOND OFF)
VHF NAV Control Panel Figure 5
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