Fault Message:

ADLU VHF MODEM FAULT

Fault Code:

2320008TDY

Associated CAS:

None

Airborne Data-Link Unit (ADLU) sets Very High Frequency Communication Unit (VHF COMM) message when no VHF communication detected.

• Airborne Data-Link Unit (ADLU) (A239)
• Very High Frequency (VHF) Modem
• Very High Frequency Communication Unit (VHF COMM) Unit 3 (A226)
• Very High Frequency Communication Unit (VHF COMM) Antenna 3 (E56)
• Radio System Bus (RSB)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

No connection can be made with the VHF Modem. Failure bit is set when VHF Modem access fails and cleared when VHF Modem access succeeds. User must initiate action to set/clear this bit. Make sure aircraft is within VHF range of ACARS data communication ground station and VHF COM #3 is operative.

1. Ensure that the VHF coverage and VHF ACARS services are available (May need to coordinate with the VHF ACARS ground service provider).
2. Check the VHF COM 3 system components and/or functions are satisfactory.

   1. If VHF COM 3 system can receive and/or transmit data, do close out.
   2. If VHF COM 3 system cannot receive and/or transmit data or one of its other functions is not available, continue with next step.

3. Check if VHF COM 3 is energized.

   1. If the unit does not receive power, troubleshoot power source from SPDA 4 and do close out.
   2. If the unit receives power, continue with next step.

4. After the Power On Self Test (POST), does the Radio Management Unit (RMU) display the RADIO TUNING Page?

   1. If YES, go to step 6.
   2. If NO, continue with next step.

5. Go to the SYSTEM TEST RESULTS and the RADIO TEST RESULTS pages. Is one or more of the following error messages displayed?
   

   RMU Page	Fault Message	Result
   SYSTEM TEST RESULTS	CHK RMU 1 (2)
   SYSTEM TEST RESULTS	CHK COM 3 UNIT
   RADIO TEST RESULTS	RMU 1 (2) ERR
   RADIO TEST RESULTS	COM 3 UNIT
   RADIO TEST RESULTS	COM 3 ERR

   1. If YES, perform the appropriate troubleshooting and do close out.
   2. If NO, continue with next step.

6. Perform the operational test of the VHF COM 3 unit (AMM 23-11-01-710-801).

   1. If the RMU displays a red ERR legend, perform the appropriate troubleshooting and do close out.
   2. If the RMU displays a PASS legend, continue with next step.

7. Perform a wiring check between VHF COM unit 3 (A226P1) and SPDA 4 (A16P1).

   1. If wiring checks are not good, repair defective wiring and do close out.
   2. If wiring checks are good, continue with next step.

8. Perform a wiring check of the VHF COM 3 antenna cable between the unit mounting tray (A226P3) and the antenna connector (E56).

   1. If wiring checks are not good, repair defective wiring and do close out.
   2. If wiring checks are good, continue with next step.

9. Re-install the VHF COM 3 unit and perform a resistance check at the antenna connector (E56). The resistance between the center conductor and the outer conductor should be approximately 50 Ohms.

   1. If the resistance check is not good, repair defective wiring or replace VHF COM 3 unit as required and do close out.
   2. If the resistance check is good, continue with next step.

10. Operate the Airborne Data-Link System using VHF network to receive the terminal text weather information. Is the terminal text weather information displayed?
    NOTE: Do the initialization of the Flight Management System (FMS). Deactivate SATCOM and Telephony systems by respective circuit breakers.
    

    1. If YES, Verify that CAIMS fault code 2320008TDY "ADLU VHF MODEM FAULT" is not displayed on PMAT and do close out.
    2. If NO, continue with next step.

11. Perform wiring checks, short to ground and pin/socket retention check between the ADLU connector A239BP1 and the VHF COM #3 connector A226P1. Is it satisfactory?

    1. If NO, repair or replace the defective wiring as required per WM 20-12 and do close out.
    2. If YES, continue with next step.

12. Replace the Airborne Data-Link Unit (ADLU) (ADLU VHF MODEM FAULT is faulty).
13. Do close out.