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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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03/10/21

Message Overview:

Message Name:

NO LDU-A BUS OUTPUT

Message Code:

B3-007035

Associated CAS:

None

Reporting LRU: LDU
System Description: 31-41-00
Schematic Diagram: 31-41-00
Wiring Diagram: 31-52-01
31-52-03

Message Description:

A-LDU-1 bus is reported inoperative by Data Concentrator Unit (DCU) channel A and Data Concentrator Unit (DCU) channel B.

Possible Causes:

  • Lamp Driver Unit (LDU) (A52)
  • Data Concentrator Unit (DCU) (A14)
  • Associated Wiring

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

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
Removal of the Lamp Driver Unit AMM 31-52-01-000-801
Installationof the Lamp Driver Unit AMM 31-52-01-400-801
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02

Troubleshooting Recommendations:

  1. Reset ANNUNCIATOR CTRL 1 Circuit Breaker CB1-D3, EICAS DCU A Circuit Breaker CB1-D1 and EICAS DCU B Circuit Breaker CB2-D1. Is the fault message still present?

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

  2. Do wiring check between DCU (A14) and LDU (A52) for the following wires:

    From To Result Notes
    Conn. A14DP1 - 4A Conn. A52P1 - 69 1
    Conn. A14DP1 - 4B Conn. A52P1 - 70 1

    1. If the check is satisfactory, continue with next step.
    2. If the check is not satisfactory, repair defective wiring.
      NOTE 1: For A/C 20001 to 20124 Post IFIS STC ST01732LA-D or A/C 20003 to 20124 Post SB 100-46-06, there is a harness extension for the LDU, therefore the wiring check must done up to connector A52BP1.

  3. Replace LDU (A52). Is the fault message is still present?

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

  4. Replace DCU (A14).
  5. Do close out.

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