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(WARNING)
RED MESSAGE (CAUTION)
AMBER MESSAGE (ADVISORY)
CYAN MESSAGE (STATUS)
WHITE MESSAGE Require immediate crew attention. These messages are accompanied by flashing master warning, triple chime attenson with or without voice message or dedicated tone. Require immediate crew awareness and future crew action may be required in the form of alternate system selection or performance limitation. These message are accompanied by flashing master caution and a single chime. Indicate safe or normal system operation which require crew awareness, over and above the dark cockpit philosophy. Indicate minor failures or reduction in systems capability, which require no crew action.

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02/18/21

Message Overview:

Message Name:

NO LB-RIU-8 BUS OUTPUT

Message Code:

B3-007799

Associated CAS:

None

Reporting LRU: RIU 1
System Description: 23-51-00
Schematic Diagram: 23-51-00
Wiring Diagram: 23-51-21
23-51-23

Message Description:

LB-RIU-8 bus absent at L-TDR and L-HF.

Possible Causes:

  • Left Radio Interface Unit (RIU) 1 (A17)
  • Junction Box 1 (JB1)
  • Air Traffic Control (ATC) Transponder 1 (A31)
  • HF Transceiver 1 (A61)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the HF Transceiver AMM 23-12-01-000-801
Installation of the HF Transceiver AMM 23-12-01-400-801
Removal of the Radio Interface Unit (RIU) AMM 23-51-21-000-801
Installation of the Radio Interface Unit (RIU) AMM 23-51-21-400-801
Removal of the Junction Boxes AMM 24-63-01-000-802
Installation of the Junction Boxes AMM 24-63-01-400-802
Removal of the Air Traffic Control (ATC) Transponder AMM 34-54-01-000-801
Installation of the Air Traffic Control (ATC) Transponder AMM 34-54-01-400-801
Standard Practices - Replace Wiring SPM 20-12-00-02
Standard Practices - Wire Repair SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Reset RIU 1A (CB1-B5) and RIU 1B/AURAL (CB1-B4) circuit breaker.

    1. If system check passes, do close out.
    2. If fault remains, continue with next step.

  2. Do the wiring check of the ARINC 429 data bus LA-RIU-8 between RIU 1 connector A17P1, through Junction Box #3, to the ATC 1 connector A31P2 and the HF Transceiver 1 connector A61P1. Repair/replace as required.

    1. If system check passes, do close out.
    2. If fault remains, continue with next step.
      NOTE: An internal short of any LRUs connected to this data bus might cause this failure.

  3. Swap ATCs.

    1. If system check passes, do close out.
    2. If fault remains, continue with next step.

  4. Swap HF Transceivers.

    1. If system check passes, do close out.
    2. If fault remains, continue with next step.

  5. Replace the left RIU.
  6. Do close out.

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