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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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03/04/21

Message Overview:

Message Name:

NO A-DCU-4 BUS OUTPUT

Message Code:

B3-006491

Associated CAS:

None

Reporting LRU: DCU 1
System Description: 31-41-00
Schematic Diagram: 31-41-00
Wiring Diagram: 31-41-01
31-41-02
31-41-11
31-41-13

Message Description:

No A-DCU-4 bus data received at 1 of (IASC1-A, IASC1-B) and 1 of (IASC2-A, IASC2-B).

Possible Causes:

  • Data Concentrator Unit (DCU) (A14)
  • Left Integrated Air System (IAS) Controller (IASC 1) (A55)
  • Right Integrated Air System (IAS) Controller (IASC 2) (A56)
  • Cockpit Voice Recorder (CVR) (A129)
  • Recorder Independent Power Supply (RIPS) (A229)
  • Junction Box 4 (JB4)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the Integrated Air System (IAS) Controller AMM 21-31-01-000-801
Installation of the Integrated Air System (IAS) Controller AMM 21-31-01-400-801
Removal of the Cockpit Voice Recorder (CVR) AMM 23-71-01-000-801
Installation of the Cockpit Voice Recorder (CVR) AMM 23-71-01-400-801
Removal of the Recorder Independent Power Supply (RIPS) AMM 23-71-25-000-801
Installation of the Recorder Independent Power Supply (RIPS) AMM 23-71-25-400-801
Removal of the Junction Box JB4 AMM 24-63-13-000-802
Installation of the Junction Box JB4 AMM 24-63-13-400-802
Removal of the Data Concentrator Unit (DCU) AMM 31-41-01-000-802
Installation of the Data Concentrator Unit (DCU) AMM 31-41-01-400-802
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Reset EICAS DCU A Circuit Breaker CB1-D1. Is the fault message still present?

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

  2. Remove CVR (A129). Is the fault message still present?

    1. If YES, continue with next step.
    2. If NO, replace defective CVR.
      NOTE: For Aircraft with the RIPS installed (20292 to 20407 post SB 100-23-20 and 20408 to 20500), the RIPS must be suspected as the defective unit causing a short circuit of the data bus. It must be removed to confirm the failure.

  3. Re-install CVR (and RIPS when required).
  4. Remove IASC 1 (A55). Is the message B3-006923 (ATA21) present in MDC current fault?

    1. If YES, continue with next step.
    2. If NO, replace defective IASC 1.

  5. Re-install IASC 1 (A55).
  6. Remove IASC 2 (A56). Is the message B3-006905 (ATA21) present in MDC current fault?

    1. If YES, continue with next step.
    2. If NO, replace defective IASC 2.

  7. Re-install IASC 2 (A56).
  8. Do wiring check between DCU (A14), IASC 1 (A55), IASC 2 (A56) and the CVR (A129), through Junction Box 4, for the following wires:

    From: To: Result:
    Conn A14FP1 - 5A Conn. A55P2 - 34
    Conn A14FP1 - 5B Conn. A55P2 - 7
    Conn A14FP1 - 5A Conn. A55P4 - 53
    Conn A14FP1 - 5B Conn. A55P4 - 60
    Conn A14FP1 - 5A Conn. A56P2 - 34
    Conn A14FP1 - 5B Conn. A56P2 - 7
    Conn A14FP1 - 5A Conn. A56P4 - 53
    Conn A14FP1 - 5B Conn. A56P4 - 60
    Conn A14FP1 - 5A Conn. A129P1 - 26
    Conn A14FP1 - 5B Conn. A129P1 - 25

    1. If the check is satisfactory, continue with next step.
    2. If the check is not satisfactory, repair wire or replace defective JB4.

  9. Replace DCU (A14).
  10. Do close out.

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