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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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02/25/21

Message Overview:

Message Name:

FAULT

Message Code:

B3-007071

Associated CAS:

ELECTRICAL FAULT
(Caution)

ELECTRICAL FAULT
(Advisory)

Reporting LRU: L ESS CNTOR
System Description: 24-61-00
Schematic Diagram: 24-61-00
Wiring Diagram: 24-61-01

Message Description:

The Left Essential Bus Contactor (LESSC) has failed.

Possible Causes:

  • Left Essential Bus Contactor (LESSC) (K77)
  • Left DC Power-Center Primary-Logic (LLOG) (PCB3)
  • Left DC Power Center (LDCPC) (A35)

Troubleshooting Tips:

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

Quick Links:

Removal of the Power Center (DCPC) AMM 24-61-01-000-801
Installation of the Power Center (DCPC) AMM 24-61-01-400-801
Removal of the Essential Contactor AMM 24-61-25-000-801
Installation of the Essential Contactor AMM 24-61-25-400-801
Removal of the DC Power-Center Primary-Logic AMM 24-61-73-000-801
Installation of the DC Power-Center Primary-Logic AMM 24-61-73-400-801
Wiring - Maintenance Practices - ALL SPM 20-12-00-02
Wire Repair - Maintenance Practices - ALL SPM 20-12-10-02
Electrical Connectors - Maintenance Practice - ALL SPM 20-20-00-02

Troubleshooting Recommendations:

  1. Disconnect the Left Essential Bus Contactor (K77) connector located in the Left DC Power Center (A35). Do visual inspection of the connector and associated wiring for any loose pins and/or damaged wire.

    1. If inspection is satisfying, continue with next step.
    2. If inspection is not satisfying, go to step 5.

  2. Verify Left Essential Bus Contactor (K77) coils by measuring the resistances at the contactor connector (J-side) as per the following table:

    Coils Expected Values Results
    Pin 1 and Pin 2 (Pick-up) between 4.5Ω and 6.5Ω
    Pin 2 and Pin 3 (Hold) between 260Ω and 280Ω

    1. If the verification is satisfying, continue with next step.
    2. If the verification is not satisfying, replace the defective Essential Bus Contactor.
      NOTE: It is important to not skip this verification before proceeding with the swap at step 3. A short of one of the 2 coils will result with a blowing of a fuse on the corresponding DC Power-Center Primary-Logic.

  3. Swap the Left Essential Bus Contactor (K77) with the Right Essential Bus Contactor (K78). Is the fault message still present?

    1. If YES, continue with next step.
    2. If NO, replace the defective Essential Bus Contactor.

  4. Swap the Left DC Power-Center Primary-Logic (PCB3) with the Right DC Power-Center Primary-Logic (PCB4). Is the fault message still present?

    1. If YES, continue with next step.
    2. If NO, replace the defective DC Power-Center Primary-Logic.

  5. Replace Left DC Power Center (A35).
  6. Do close out.

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