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channels of auto tune signals to the navigation control panel.
The navigation control panel adds one manual channel and
sends five tune channels to the DME interrogator.
Alternate Tune Input
If the navigation control panel has a failure, the FMC sends auto
signals directly to the DME interrogator.
Discrete Inputs
When the navigation control panel has a failure, it grounds a
source select discrete to the DME central processing unit (CPU).
The CPU changes the input from the navigation control panel to
the FMC.
The proximity switch electronics unit (PSEU)supplies an air/
ground discrete to prevent a DME test when the aircraft is in the
air. The discrete also supplies flight leg data.
Operation
The CPU uses tune inputs to tune the frequency synthesizer.
The CPU give a signal to the transmitter to send interrogation
pulses. The transmit pulses go through a circulator then to the
DME antenna.
The transmitter sends a signal to the suppression circuits.
During a transmission, the suppression circuit in the DME 1
interrogator sends a suppression pulse to these units:
* DME 2 interrogator
* ATC 1 and 2 transponders (XPNDR)
* TCAS computer.
The suppression pulse stops receiver operation in the other
LRUs to prevent damage to internal circuits.
Receive
The circulator sends the RF pulse pairs it receives from the
antenna to the receiver. The receiver sends the pulse pair to the
CPU. The CPU calculates the slant range distance. It uses the
time it takes to transmit pulse pairs and get a reply from the
ground station. When another L-band system transmits, a
suppression pulse stops the receiver operation.
Interrogator Output
After the CPU calculates slant range distance, the CPU sends it
to two ARINC 429 transmitters. One ARINC 429 transmitter
sends the range data to the DEUs for the flight deck displays
and to other systems. A second ARINC 429 transmitter sends
range data to the flight control computer. The CPU sends the
pulse pairs to the pulse pair decoder. The decoder sends the
DME audio to the REU.
DME SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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Bite Module
The built-in test equipment (BITE) in the CPU monitors the
circuits in the DME interrogator for faults. The fault memory in
the DME keeps the number of faults per flight. Shop personnel
can read the fault memory contents.
Test
The CPU does a test of the interrogator when it receives a test
command from the navigation control panel. You can also push
the test switch on the front panel of the interrogator. The LEDs
on the front panel of the interrogator do not show during the
navigation control panel test.
DME SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 34-55-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-55-00-012
DME SYSTEM - FUNCTIONAL DESCRIPTION
DME SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 34-55-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-55-00-012
Self Test
Push the test switch on the DME interrogator to start a DME selftest.
Front Panel Displays
The LED status indicators go through this sequence:
* The LRU status and control fail LEDs come on red for two
seconds.
* The LRU status LED changes to green.
* All LEDs go off for two seconds.
* The applicable LEDs come on to show the LRU status.
The red CONTROL FAIL LED shows when the tuning source is
invalid.
The LRU STATUS LED shows interrogator test results. The LRU
STATUS LED shows green for a good test or it shows red for a
test failure.
DME SYSTEM - SELF TEST
EFFECTIVITY
SHZ ALL 34-55-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-55-00-014
DME SYSTEM - SELF TEST
DME SYSTEM - SELF TEST
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
34-55-00-014
General
During a ground test or a self test, the display units show these
　
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