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You can do a test of the VOR/MB receiver from the maintenance access terminal (MAT) or from the test switch on the VOR/MB receiver front panel. When you do a test of the left VOR/MB receiver, you do a test of the VOR function and the marker beacon function in the left VOR/MB receiver at the same time.
Flight Fault Memory
The VOR/MB receiver has a non-volatile flight fault memory. Only shop personnel can read the memory on the test bench.
Training Information Point
The maintenance manual and the fault isolation manual do not have a task for the line maintenance technician to do a test from the front panel of the VOR/MB receiver. You must do all tests for the VOR/MB receiver from the MAT or a PMAT.
Many LRUs on the 777 are compatible with other model airplanes that do not have a central maintenance computing system (CMCS). For that reason these LRUs have a front panel test feature.
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777 AIRCRAFT MAINTENANCE MANUAL

VOR -VOR/MB RECEIVER

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VOR -ANTENNA

General
The VOR antenna is on the top of the vertical stabilizer. The VOR antenna receives RF signals in the frequency range of 108 MHz to 117.95 MHz. The antenna receives VOR and ILS frequencies. The VOR antenna sends VOR signals to both VOR/ MB receivers.
The VOR antenna has two outputs, one to each VOR receiver.
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777 AIRCRAFT MAINTENANCE MANUAL

VOR -ANTENNA

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VOR -VOR/MB RECEIVER FUNCTIONAL DESCRIPTION

General
The receiver has both VOR and marker beacon functions. This section only covers the VOR functions.
Operation
Manual or autotune inputs from the AIMS cabinets, or alternate tune inputs from the CDUs go through the input port switch then to the processor. The processor sends them to the frequency synthesizer to tune the receiver circuits.
The left AIMS cabinet sends test/status commands and flight legs discrete to the VOR receiver. When the processor receives a test command, it does a check of the VOR/MB receiver operation and control input status. Results of the test show on the MAT. Test results show on the control input and LRU status LEDs when you do a test from the front panel of the VOR/MB receiver.
The air/ground relay discrete input inhibits a VOR test when the airplane is in the air. The receiver also uses the air ground discrete for flight legs if the AIMS flight leg discrete input fails.
The processor receives a source destination identifier (SDI) program pin discrete to designate the receiver as the left or right system receiver.
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VOR Antenna Input
Input signals from the VOR antenna go through the power divider then to the receiver circuits in the VOR/MB receiver. The receiver circuit sends any audio or Morse code station identifier signals from the ground station to the audio processor. The audio or Morse code station identifier goes to the audio output circuits then to the audio management unit.
The receiver circuit sends the antenna input signals to the bearing computer which calculates the VOR station bearing. Bearing data from the bearing computer goes to an ARINC 429 transmitter. The VOR/MB receiver transmits VOR bearing data on two output buses. The output buses go to the left and right AIMS cabinets.
The audio processor also sends Morse code station identifier signals to a Morse decoder circuit. This circuit decodes the station identifier and puts it in a digital format then sends it to the ARINC 429 transmitter. When the ND receives the digital Morse code station identifier, it replaces the VOR station frequency with the identifier.
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VOR -VOR/MB RECEIVER FUNCTIONAL DESCRIPTION

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VOR -TUNE INPUTS

General
These are the three ways to tune the VOR receivers:
*
Manually by the left, center, or right CDU

*
Automatically by the AIMS cabinets

*
By the CDUs as an alternate tune source.

Manual Tune
You manually tune the VOR receivers from the left or right control display unit (CDU). The center CDU can tune the receivers if the left or right CDU fails. Manual tune inputs from the CDUs go through the left and right systems ARINC 629 buses, then to the left and right AIMS cabinets.
The left AIMS cabinet sends manual and autotune data through the AIMS intercabinet ARINC 629 buses to the right AIMS cabinet.
　
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