Message Name:

NAVIGATION DISPLAY-UNIT (NDU) SYSTEM NOT WORKING PROPERLY

Some Navigation Display-Unit (NDU) Lamps and Displays does not comes ON, the NDU does not energize, or the Fault Lamp comes ON.

• Navigation Display-Unit (NDU) (M2)
• Integrated Avionics Computer (IAC) 1 (A11)
• Integrated Avionics Computer (IAC) 2 (A10)
• Integrated Avionics Computer (IAC) 3 (A12)
• Inertial Reference Unit (IRU) 1 (A32)
• Inertial Reference Unit (IRU) 2 (A33)
• Inertial Reference Unit (IRU) 3 (A34)
• Pilot Integral Lighting Power Supply (A183)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE: The NDU gets its primary +28 VDC power from the IRUs. If the NDU does not energize, it is possible that an IRU is defective. First go to MFD to check for IRS related EICAS message. If one or more EICAS fault messages appear, first do the IRS troubleshooting.

1. Perform the following through an IBIT, push the ON push button to energize the NDU. The NDU shows dashes in the top digital display and energizes the lamps in these function keys: SYSTEM SELECT 1, POS and M.
2. Push the TST push button to start the lamp test part of the IBIT. The NDU shows all digits in the two digital displays Energizes each lamp, in sequence, in these function keys: WPT LEG CHG, XTK DTK, DIS TIM, TK GS, POS, WD WS, HDG STS, SYSTEM SELECT 1, 2, 3, FAULT, ENT, CLR, M, and T.
3. After the IBIT stops, a serviceable NDU will energize the lamps in these function keys: SYSTEM SELECT 1, POS, and M.
4. Check if the FAULT lamp comes on.

   1. If the FAULT lamp comes on and/or if the lamp test is unsatisfactory, go to step 13.
   2. If the FAULT lamp does not comes on or the NDU does not energize, continue with the next step.

5. Examine the NDU for defective connectors.

   1. If the NDU connector is defective, go to step 13.
   2. If the NDU connectors are not defective, continue with the next step.

6. Examine the cable assemblies for defective connectors and/or wiring.

   1. If the pins of the harness connectors are defective, replace defective pins or connectors and do close out.
   2. If a cable assembly is defective or if the damage cannot be seen, continue with the next step.

7. Remove the IRUs for access to connectors A32BP1, A33BP1 and A34BP1, and remove the IACs for access to connectors A11CP1, A10CP1 and A12CP1. Perform a continuity check between the connectors that follow:
   For the NDU, IRU 1 and IAC 1:

   NDU	IRU 1	IAC 1	Result
   M2P1-24	A32BP1-A13	A11CP1-16
   M2P1-25	A32BP1-A14	A11CP1-17
   M2P1-26	A32BP1-G7	no connection
   M2P1-27	A32BP1-G8	no connection
   M2P1-SH	A32BP1-SH	A11CP1-SH

   For the NDU, IRU 2 and IAC 2:

   NDU	IRU 2	IAC 2	Result
   M2P2-24	A33BP1-A13	A10CP1-16
   M2P2-25	A33BP1-A14	A10CP1-17
   M2P2-26	A33BP1-G7	no connection
   M2P2-27	A33BP1-G8	no connection
   M2P2-SH	A33BP1-SH	A10CP1-SH

   For the NDU, IRU 3 and IAC 3:

   NDU	IRU 3	IAC 3	Result
   M2P3-24	A34BP1-A13	A12CP1-16
   M2P3-25	A34BP1-A14	A12CP1-17
   M2P3-26	A34BP1-G7	no connection
   M2P3-27	A34BP1-G8	no connection
   M2P3-SH	A34BP1-SH	A12CP1-SH

   For the NDU connectors M2P1, M2P2 and M2P3:

   From	To	Result
   M2P1-8	M2P1-SH
   M2P2-8	M2P2-SH
   M2P3-8	M2P3-SH

   1. If there is no continuity, repair or replace the defective wiring as required and do close out.
   2. If there is continuity, continue with the next step.

8. Disconnect the electrical connector A183P1 from the lighting power supply A183. Perform a continuity check between the Navigation Display-Unit (M2) and Power Supply (A183) as follows:

   From	To	Result
   M2P1-1	A183P1-B
   M2P1-2	Ground

   1. If there is no continuity, repair or replace the defective wiring as required and do close out.
   2. If there is continuity, continue with the next step.

9. Connect the electrical connector to the lighting power supply A183. Perform a voltage check between the Navigation Display-Unit (M2) as follows:

   From	To	Expected Result	Result
   M2P1-1 (positive probe)	M2P1-2 (negative probe)	+5 VDC

   1. If there is no +5 VDC, replace the power supply and continue with the next step.
   2. If there is +5 VDC, continue with the next step.

10. Install the IACs and the IRUs. Perform a voltage check between the connectors M2P1, M2P2 and M2P3 of NDU as follows:

    From	To	Expected Result	Result
    M2P1-3 (positive probe)	M2P1-4 (negative probe)	+28 VDC
    M2P2-3 (positive probe)	M2P2-4 (negative probe)	+28 VDC
    M2P3-3 (positive probe)	M2P3-4 (negative probe)	+28 VDC

    1. If there is +28 VDC, go to step 12.
    2. If there is no +28 VDC, continue with the next step.

11. Check that the correct circuit breakers are set to IN and not LOCK, OUT, or TRIP and the MFD does not show EICAS fault messages for the IRUs.

    1. If system checks are good, do close out.
    2. If fault remains, continue with next step.

12. Perform a wiring check for power supply.

    1. If wiring checks are not good, repair defective wiring as required and do close out.
    2. If wiring checks are good, continue with next step.

13. Replace NDU.
14. Do close out.