Message Name:

ADF NO DISPLAY OR INCORRECT BEARING INFORMATION OR ADF SELF-TEST FAILURE

Automatic Direction Finder (ADF) System cannot receive or process radio frequency signal for display or fails radio self test as displayed on the Radio Management Unit (RMU).

NOTE: As a general guide line the ADF should provide operation with errors not exceeding 5 degrees, and the aural signal should be clearly audible up to the distance listed for any one of the following types of radio beacons:

• 50 NM from an H facility (Transmitter power 50 to 2000 Watts)
• 25 NM from an MH facility (Transmitter power less than 50 Watts)
• 5 NM from a Compass Locator (Transmitter power less than 25 Watts)

• Very High Frequency (VHF) Navigation Unit 1 (A3)
• Very High Frequency (VHF) Navigation Unit 2 (A4)
• Automatic Direction Finder (ADF) 1 Antenna (E3)
• Automatic Direction Finder (ADF) 2 Antenna (E4)
• Antenna Coax

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE:

• Do not replace a NAV unit that fails a ADF self-test as a first action because it will often result in a No Fault Found (NFF) situation. It is highly recommended that technician(s) should follow the Troubleshooting Recommendations: in this module prior to the replacement of the NAV unit
• The ADF radio module is not an LRU and it is installed in the NAV unit
• During WOW condition, the radio system automatically performs a Power On Self-Test (POST) which test the associated Radio System Bus (RSB) and individual modules (including ADF). The POST does not test the ADF antenna and cable. Following aircraft power up, monitor the RMU system test results show failures related to Radio System Bus (RSB) and associated units CHK amber or ERR for the modules. Pressing TST again show the Radio Test results for individual modules

1. Perform a RMU Pilot Activated Self-Test (PAST) for the affected ADF, ensure the ADF needles are selected for view on the Primary Flight displays and ADF audio is selected ON at the audio panels
2. Observe and record any active failure(s) ADF ERR codes. Observe for proper ADF needles deflection (slew) to approximately 135 ±10 degrees relative to the nose of the aircraft and the 1 KHz audio test tone is heard.

   1. If test passes, do close out.
   2. If test fails, continue with next step.

3. Perform PAST again.

   1. If test passes, do close out.
      NOTE: If test show ADF PASS at least one time, the system should be consider serviceable and no further action is required.
   2. If test fails, continue with next step.

4. Reposition the aircraft into another location and perform PAST again.
   NOTE: PAST result can be affected if PAST is performed near anything metallic (like a hanger structure, rebar in the cement and power lines), that may distort or attenuate the radio fields.

   1. If test passes, do close out.
   2. If test fails, continue with next step.

5. Swap NAV Units.

   1. If system checks are good, replace defective NAV unit and do close out.
   2. If fault remains, continue with next step.
      NOTE: Ensure that the failure code is recorded on the removal documentation (MRA).

6. Troubleshoot using failure code information.
7. On the RMU display, based on the applicable maintenance log page(s) for the messages code perform associated procedure as follows:

   Continuous Monitoring Event Code (HEX)	PAST/POST Event Code (HEX)	ASCII Description	Event Description
   04	84	DATABUS	* RCB Checksum Error
   06	86	COMPUTER	NOVRAM Read/Write Failure
   08	88	COMPUTER	Watchdog Reset has occurred
   21	A1	PWR SPLY	+5 V Power Supply
   22	A2	PWR SPLY	+15 V Power Supply
   23	A3	COMPUTER	Processor Internal RAM
   24	A4	COMPUTER	Processor External ROM
   -	A5	COMPUTER	Processor Bearing
   27	A7	ADF DATA	HF Key Failure
   28	A8	ADF TUNE	Synthesizer Lock
   --	A9	ADF RCVR	** Demodulator Lock
   --	AA	ADF RCVR	* AGC Level Out of Range
   --	AB	ADF RCVR	System Bearing
   2C	AC	ADF TUNE	Synthesizer Lo 1 Level
   2D	AD	OVERHEAT	Ambient Temperature
   NOTE: An asterisk (*) indicates that the event code is an external event. Two asterisks (**) indicate that the event code can be a result of a defective aircraft antenna or the connecting coaxial cable.

1. Code 04-84: Indicative of a Radio Communication Bus (RCB) problem at the NAV Cluster level, not necessarily the ADF module itself. Check that the NAV unit is correctly installed and check for onside RMU failure messages on the Primary and Secondary radio communication buses.
2. Code 2D-AD, Indicative of an overheat condition. Check if other module have overheat codes, verify NAV cluster code 21 (fan fails to turn on). Confirm correct operation of the NAV unit tray cooling fan. This fan operates on/off based on NAV unit cooling requirements.
3. Codes A9, AA, AB are associated to failures during self-test only (PAST/POST).For AB, it will be noticed that the bearing change (ADF needle) generated from the self-test circuit is out of range, less than 125 degrees or greater than 145 degrees. Check ADF antenna bounding (ref. Installation ADF Antennas AMM Task 34-52-01-400-801 and SPM Task 51-80-00-760-801 Electrical Bonding Test-All Globals ATA 34). The maximum resistance value should be 0.0025 Ohm If practicable, disconnect the aircraft connector from the antenna and measure from the antenna connector and check ADF antenna connectors and wiring (WD 34-51-00).
   NOTE: Prior to the troubleshooting, if the failure occurred on the ground, reposition the aircraft into another location, since the self test can be affected if near anything metallic, like a hanger structure, rebar in the cement and power lines that may distort or attenuate the radio fields.

   1. If all the checks are good, the problem may be attributed to the self-test oscillator in the antenna. Replace ADF antenna.
   2. If fault remains, continue with next step.

4. Code 27-A7, indicates that the HF KEY line is in the ON (Grounded) position continuously for more than 2 minutes and verify that the HF KEY input AP1-66 (WD 34-51-00) is not externally grounded via the Audio Integrated system Audio Panels (WD 23-51-00) or if the HF transceiver internal HF KEY circuit P1-J (WD 23-12-00) has failed.
5. For any other codes, the NAV unit is likely at fault. If practical, this can be confirmed by interchange NAV 1 and 2 units.
6. If no failure code is reported by the system, but crew reports incorrect bearing information. Verify that the Quadrantal Error Correction (QEC) adjustments via the RMU straps page, for W7 to W30 inclusive. Refer to AMM Task 34-51-01-280-801, Configuration Setting of the VHF Navigation Units.
   NOTE: Antenna performance and signal reception can be evaluated between NAV Unit 1 and NAV Unit 2. Listen for noticeable variation to the audio from the same distant AM radio station. If one of the systems seems weaker perform troubleshooting by interchanging the NAV units and similar to codes A9, AA, AB.

8. Refer the current power on count (POC) to establish correlation with the reported event by the crew. Record the ER (Error code) and interchange NAV 1 and 2 and monitor for failures on subsequent flight or follow troubleshooting recommendation per the above step 7.
9. Do close out.