Message Name:

HST MDU[CH1]/MOTOR #1/ACT/WRG FAULT

Message Code:

27662281SX

Associated CAS:

STAB TRIM
(Caution)

SPLRS STAB BIT
(Advisory)

STAB CH1 FAIL
(Advisory)

CAIMS reports a Motor Drive Unit (MDU) Channel no response or a Actuator/Motor Jam.

• Pitch Trim Actuator Motor Drive Unit (A184)
• Pitch-Trim Actuator (B44)
• Flight Control Unit (FCU) 1 (A65)
• Pilot Master Disconnect Switch (S45)
• Copilot Master Disconnect Switch (A44)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

NOTE 1: The present MDU-5 is known to be susceptible to nuisance coasting if there is a fast trim cycle of NOSE-UP or NOSE-DOWN. To prevent unnecessary troubleshooting and component removal after an occurrence of this phenomenon, it is recommended to do Flight Control Systems reset procedure before the next flight to determine if the STAB CH1 FAIL or STAB CH2 FAIL advisory or STAB TRIM caution message shows. If one of these messages still show after the self-test, it is necessary to do troubleshooting. If during subsequent flights a STAB CH1 FAIL or STAB CH2 FAIL message shows more than once in 10 flight legs, we suggest that operators record the CAIMS flight fault history for FCU 1 and FCU 2 if the faults reported are:

• H STAB MOT DR UNIT [CH1]/WRG FAULT
• H STAB MOT DR UNIT [CH2]/WRG FAULT

It can be necessary to replace the motor drive unit. Contact your local field service representative for further troubleshooting.

NOTE 2: You can use the MDU inverting Harness to help with troubleshooting.

1. On the PMAT, access CAIMS and make the following selections:

   1. System Diag
   2. ATA 27 Flight Controls
   3. Flight Control Unit 1 or 2 (as applicable)
   4. LRU TEST

2. From the LRU TEST menu, select COCKPIT SWITCHES TEST [FCU 1] or [FCU2]. Follow the instructions on the PMAT. Did the test pass?

   1. If YES, go to step 4.
   2. If NO, continue with next step.

3. Perform wiring checks between FCU 1 and FCU 2 to the Pilot and Copilot master disconnect switch.
   NOTE: The master disconnect switch is not easy to access; the verification can be performed by doing a continuity check of the wire from the FCU through the switch and by selecting the switch.

Pilot Master Disconnect Switch	From	To	Normal Status
Switch Selected	A65AP1-8G	A66AP1-8G	open to ground
Switch Not Selected	A65AP1-8G	A66AP1-8G	shorted to ground

Copilot Master Disconnect Switch	From	To	Normal Status
Switch Selected	A65DP1-8D	A66DP1-8D	open to ground
Switch Not Selected	A65DP1-8D	A66DP1-8D	shorted to ground

NOTE: wires color code on the Pilot Master Disconnect switch:

PIN (wire color)	PIN (wire color)	CONTACTS (Switch NOT Selected)	CONTACTS (Switch Selected)
A3 (blue)	A2 (white)	CLOSED	OPEN
B3 (violet)	B2 (grey)	CLOSED	OPEN
C3 (white/black)	C2 (white/orange)	CLOSED	OPEN
D4 (yellow)	D1 (white/grey)	OPEN	CLOSED

Make sure the pins on the terminal Module in the control wheel are locked properly. The terminal modules are not shown in the wiring diagram and system schematic.

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.

4. Perform SPOST 1 and SPOST 2 of the FCUs at least twice. Is the fault still present?

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

5. Interchange FCU 1 with FCU 2. Is the fault still present?

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

6. Use the Ground support Equipment 27X-41-09 "MDU INVERTING HARNESS" to isolate the fault to the MDU or pitch trim Actuator, prior to replacing any units.

   1. If the fault is suspected to be with the MDU, go to step 10.
   2. If the fault is suspected to be with the HSTA, continue with next step.

7. Perform continuity checks between MDU and HSTA as follow:

   From	To	Result
   A184P2-A	B44P1-A
   A184P2-B	B44P1-B
   A184P2-C	B44P1-C

   From	To	Result
   A184P3-1	B44P2-34
   A184P3-2	B44P2-26
   A184P3-3	B44P2-12
   A184P3-4	B44P2-11
   A184P3-10	B44P2-32
   A184P3-25	B44P2-33
   A184P3-19	B44P2-14
   A184P3-20	B44P2-13

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

8. Perform a continuity checks as follow:

   From	To	Result
   A184P2-A	Ground
   A184P2-B	Ground
   A184P2-C	Ground

   From	To	Result
   A184P3-1	Ground
   A184P3-2	Ground
   A184P3-3	Ground
   A184P3-4	Ground
   A184P3-10	Ground
   A184P3-25	Ground
   A184P3-19	Ground
   A184P3-20	Ground

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

9. Interchange the HSTA motors. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, replace defective HSTA motor and do close out.

10. Replace the MDU.
11. Do close out.