Frequency tune inputs from the NAV control panel go to an ARINC 429 receiver in the VOR / MB receiver, then to the processor. The processor sends the tune inputs to the frequency synthesizer to tune the receiver circuits.
The control panel sends a discrete to the REU when you tune a VOR frequency. The REU uses the discrete to select VOR audio inputs.
When you tune a VOR frequency, the control panel also sends a discrete to the DEUs. The DEUs use the discrete to display VOR or ILS as the frequency data source on the lower left corner of the captain and first officer NAV displays.
The processor sends fault data to the memory card. Only shop personnel can read the memory card contents.
The air / ground discrete input from the PSEU inhibits a VOR test when the airplane is in the air. The receiver also uses the discrete for flight leg count.
RF input signals from the VOR / ILS antenna go through the power divider then to the receiver circuits in the VOR / MB receiver. The receiver circuits send audio and morse code station identifier signals from the ground station to the audio processor.
The audio processor sends the audio and morse code station identifier signal to the audio output circuits then to the remote electronics unit.
The morse decoder circuit decodes the station identifier and puts it in digital format then sends it to the ARINC 429 transmitter. The display electronic units (DEU 1 & 2), use the data to show the station identifier.
The VOR / MB VOR receiver circuits send the antenna inputs to the bearing processor which calculates the VOR station bearing. Data from the bearing processor goes to the ARINC 429 transmitter. The VOR / MB receiver transmits VOR bearing and receiver status on two output buses.
Output bus 1 goes to the onside FCC. Output bus 2 goes to these components:
· Flight data acquisition unit (FDAU)
· Radio magnetic indicator (RMI)
· Flight management computers (FMC)
· Display electronic units (DEU).
When you push the test switch on the NAV control panel, a test command goes to the receiver when a VOR frequency is the active frequency. When the processor receives a test command, it monitors the VOR / MB receiver operation and control input status. Test results show on the status LEDs when you do a test from the front panel switches.