Message Name:

NO BATT BUS PWR
(Service Message)

Message Code:

B3-006323

Associated CAS:

None

Primary voltage to Auxiliary Power Unit (APU) Electronic Control Unit (ECU) less than 10 VDC.

• Auxiliary Power Unit (APU) Circuit Breaker (CB1-B8)
• Auxiliary Power Unit (APU) Master Switch (S89)
• Auxiliary Power Unit (APU) Master Relay (K61) (located in the R SPC)
• Auxiliary Power Unit (APU) Electronic Control
• Left Cockpit Circuit Breaker Panel (CBP1)
• Right Secondary Power Center (R SPC) (A38)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: The APU Master Switch must be selected at RUN (or START) to provide the primary power to the APU ECU.

1. Confirm presence of the Ground at the APU ECU (A39).

   Measurement at	Expected Result	Result
   Conn. A39CP1-3	Aircraft Ground

   1. If check is satisfactory, continue with next step.
   2. If check is not satisfactory, repair defective wiring.

2. Confirm presence of the 28 VDC (Primary Power) at the APU ECU (A39).

   Measurement at	Expected Result	Result
   Conn. A39CP1-1	28 VDC

   1. If check is satisfactory, go to step 12.
   2. If check is not satisfactory, continue with next step.

3. Do wiring check from the Right SPC (A38) to APU ECU (A39) for the following wires:

   From	To	Result
   Conn. A38P2-V	Conn. A39CP1-1

   1. If the check is satisfactory, continue with next step.
   2. If the check is not satisfactory, repair defective wiring.

4. Confirm presence of the 28 VDC at the R SPC (A38).

   Measurement at	Expected Result	Result
   Conn. A38P2-U	28 VDC

   1. If check is satisfactory, go to step 7.
   2. If check is not satisfactory, continue with next step.

5. Do wiring check from the Right SPC (A38) to Left Cockpit Circuit-Breaker Panel (CBP1) for the following wires:

   From	To	Result
   Conn A38P2-U	CBP1J2-U

   1. If the check is satisfactory, continue with next step.
   2. If the check is not satisfactory, repair defective wiring.

6. Replace APU Circuit Breaker CB1-B8. Is the fault message still present?

   1. If NO, do close out.
   2. If YES, replace defective left Cockpit Circuit-Breaker Panel (CBP1).

7. Confirm presence of the Ground at the R SPC (A38).

   Measurement at	Expected Result	Result
   Conn A38P1-1	Aircraft Ground

   1. If the check is satisfactory, continue with next step.
   2. If the check is not satisfactory, go to step.
      NOTE:The APU Master Switch must be selected at RUN (or START) to provide the ground at the R SPC.

8. Swap Relay K61 with Relay K130 (both located in R SPC). Is the fault message still present?

   1. If YES, replace defective R SPC.
   2. If NO, replace defective relay K61.
      NOTE: Relay K130 belongs to the AIR DATA no.2 power circuitry. K18, K20, K132 could also be used during swap test instead of K130.

9. Do wiring check from the Right SPC (A38) to the APU Master Switch (S89) (located on the FUEL Control Panel (PL35)) for the following wires:

   From	To	Result
   Conn. A38P1-1	S89P1 - H

   1. If the check is satisfactory, continue with next step.
   2. If the check is not satisfactory, repair defective wiring.

10. Confirm presence of the Ground at the APU Master Switch (S89).

    Measurement at	Expected Result	Result
    Conn, S89P1-E	Aircraft Ground
    Conn, S89P1-F	Aircraft Ground

    1. If the check is satisfactory, continue with next step.
    2. If the check is not satisfactory, repair defective wiring.

11. Check proper operation of the APU Master Switch (S89) by connecting a multimeter at S89J1 - F and S89J1 - H.

    Switch Setting	Contacts	Expected Result	Result
    OFF	Open	No continuity
    RUN	Closed	Continuity
    START	Closed	Continuity

    1. If the check is satisfactory, continue with next step.
    2. If the check is not satisfactory, replace defective APU Master Switch (S89).

12. Replace APU ECU (A39).
13. Do close out.