Message Name:

VHF COM CANNOT TRANSMIT OR RECEIVE

The Very High Frequency Communication (VHF COM) System cannot receive and/or transmit data or one of its other functions is not available.

• Very High Frequency (VHF) Communication Unit 1 (A1)
• Very High Frequency (VHF) Communication Unit 2 (A2)
• Very High Frequency (VHF) Communication Unit 3 (A226)
• Very High Frequency (VHF) Antenna 1 (E15)
• Very High Frequency (VHF) Antenna 2 (E16)
• Very High Frequency (VHF) Antenna 3 (E56)
• Very High Frequency (VHF) Communication In-line Filter (FL2)
• Associated Wiring

Advisory Wire/Service Bulletin:

• AW700-23-0499 - Use of Commercially Available Aviation Headsets

Forum Articles/Infoservice/Newsletter: None

1. Make sure the affected VHF COM unit is powered.

   1. If the affected VHF COM unit circuit breaker is set to OUT, set it to IN and do close out.
   2. If the circuit breaker is set to IN, continue with next step.

2. Make sure that power is getting to the VHF COM unit by performing a voltage check at the affected VHF unit connector (Use SSM 23-11-00).

   1. If power is not present, investigate power source and wiring and rectify as required.
   2. If power is present, continue with next step.

3. Apply full power to the A/C. The Power On Self Test (POST) will be performed automatically. After the POST stops, does the Radio Management Unit (RMU) display the RADIO TUNING page?

   1. If YES, go to step 8.
   2. If NO, continue with next step.

4. Check if the active fault message CHK RMU 1 (2) is displayed.

   1. If YES, perform troubleshooting for 314OBS003 and do close out.
   2. If NO, continue with next step.

5. Check if the active fault message CHK COM 1 (2) (3) UNIT is displayed.

   1. If YES, perform troubleshooting for 314OBS003 and do close out.
   2. If NO, continue with next step.

6. Check if the active fault message RMU 1 (2) ERR is displayed.

   1. If YES, perform troubleshooting for 238OBS001 and do close out.
   2. If NO, continue with next step.

7. Check if the active fault messages COM 1 (2) (3) ERR and COM 1 (2) (3) UNIT are displayed.

   1. If NO, do close out.
   2. If YES, continue with next step.

8. Swap VHF COM unit. Is the fault still present?

   1. If NO, go to step 19.
   2. If YES, continue with next step.

9. Disconnect the VHF COM 1 connector (A1P1), VHF COM 2 connector (A2P1), VHF COM 3 connector (A226P1), LGECU connector (A52AP1), VHF NAV 1 connector (A3AP1), VHF NAV 2 connector (A4AP1) and TCAS connector (A7CP1). Perform a continuity check of the wiring interface of the affected VHF COM unit as follows:
   VHF COM 1:

   From	To	Result
   WOW
   A1P1-83	A52AP1-F13
   SIMULCOM
   A1P1-35	A2P1-35
   A1P1-35	A226P1-35
   A1P1-24	A2P1-24
   A1P1-24	A226P1-24
   MUTUAL SUPPRESSION (MUT SUP)
   A1P1-94	A2P1-94
   A1P1-94	A3AP1-42
   A1P1-94	A4AP1-42
   A1P1-94	A7CP1-12

   VHF COM 2:

   From	To	Result
   WOW
   A2P1-83	A52AP1-E14
   SIMULCOM
   A2P1-35	A1P1-35
   A2P1-35	A226P1-35
   A2P1-24	A1P1-24
   A2P1-24	A226P1-24
   MUTUAL SUPPRESSION (MUT SUP)
   A2P1-94	A1P1-94
   A2P1-94	A3AP1-42
   A2P1-94	A4AP1-42
   A2P1-94	A7CP1-12

   VHF COM 3:

   From	To	Result
   BURST TUNE
   A226P1-26	Ground
   SIMULCOM
   A226P1-35	A1P1-35
   A226P1-35	A2P1-35
   A226P1-24	A1P1-24
   A226P1-24	A2P1-24

   1. If there is no continuity, repair defective wiring as required and do close out.
   2. If there is continuity, continue with next step.

10. Access the MAINTENANCE LOG page on the RMU. Did one or more of the fault messages in the table below display as active or stored fault?

    RMU page (from MAINTENANCE LOG page)	Fault Message	Fault Code
    COM	COMPUTER	B2, B3
    COM	COM RCVR	A8, A9
    COM	COM TUNE	AA, A6, B1
    COM	MODULATR	AF
    COM	OVERHEAT	A7
    COM	PWR SPLY	A1, A2, A3, A4, A5
    COM	SQUELCH	AB, AC
    COM UNIT	CODE ERR	A5
    COM UNIT	COMPUTER	A4
    COM UNIT	FPGA ERR	B0
    COM UNIT	RAM ERR	A1, A2, A3, 2A
    COM UNIT	RSB PRI	AB
    COM UNIT	RSB SEC	AC
    COM UNIT	RSB TX	AD, AE
    COM UNIT	STRAPS	A6

    1. If YES, go to step 19.
    2. If NO, continue with next step.

11. Did the following fault display as active or stored fault?

    RMU page (from MAINTENANCE LOG page)	Fault Message	Fault Code
    COM UNIT	STRAPS	A7

    1. If NO, go to step 15.
    2. If YES, continue with next step.

12. Compare the given strap settings to those specified for the A/C configuration. Do the strap settings agree?

    1. If NO, rectify the strap settings using AMM task 23-11-01-280-801 and do close out.
    2. If YES, continue with next step.

13. Perform a continuity check of the COM/NAV dual Straps of the affected VHF COM UNIT as follows:
    VHF COM 1 to STRAP Board 1:

    From	To	Result
    A1P1-102	A5-2
    A1P1-88	A5-6
    A1P1-16	A5-3
    A1P1-101	A5-7
    A1P1-43	A5-4

    VHF COM 2 to STRAP Board 2:

    From	To	Result
    A2P1-102	A6-2
    A2P1-88	A6-6
    A2P1-16	A6-3
    A2P1-101	A6-7
    A2P1-43	A6-4

    1. If there is no continuity, repair defective wiring as required and do close out.
    2. If there is continuity, continue with next step.

14. Did the following fault display as active or stored fault?

    RMU page (from MAINTENANCE LOG page)	Fault Message	Fault Code
    COM UNIT	COM XMTR	2D

    NOTE: This fault can identify a defective coaxial cable, in-line filter or antenna.

    1. If NO, go back to step 3 for fault confirmation. If fault is no longer present, do close out.
    2. If YES, continue with next step.

15. Disconnect the VHF COM 1 Antenna connector (E15P1), VHF COM 2 Antenna connector (E16P1) and VHF COM 3 Antenna connector (E56P1). Perform a continuity check as follows:
    VHF COM 1:

    From	To	Expected Result	Result
    A1P3 Center conductor	Ground	Open
    A1P3 Center conductor	A1P3 Outer conductor (Shield)	Open
    A1P3 Center conductor	E15 Center conductor	Continuity
    A1P3 Outer conductor (Shield)	E15 Outer conductor (Shield)	Continuity

    VHF COM 2:

    From	To	Expected Result	Result
    A2P3 Center conductor	Ground	Open
    A2P3 Center conductor	A2P3 Outer conductor (Shield)	Open
    A2P3 Center conductor	E16 Center conductor	Continuity
    A2P3 Outer conductor (Shield)	E16 Outer conductor (Shield)	Continuity

    VHF COM 3:

    From	To	Expected Result	Result
    A226P3 Center conductor	Ground	Open
    A226P3 Center conductor	A226P3 Outer conductor (Shield)	Open
    A226P3 Center conductor	E56 Center conductor	Continuity
    A226P3 Outer conductor (Shield)	E56 Outer conductor (Shield)	Continuity

    1. If there is no continuity, repair or replace defective coaxial cable as required or replace defective in-line filter as required and do close out.
    2. If there is continuity, continue with next step.

16. Refer to SPM 51-80-00 (Electrical Bonding Test) and perform a bonding test between the VHF antenna structure and aircraft structure.

    1. If bonding resistance is within limits, continue with next step.
    2. If bonding resistance is not within limits, rectify/replace as required and do close out.

17. Perform the operational test of the VHF COM system.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

18. Replace defective VHF COM unit.
19. Do close out.