Message Name:

HST MDU[CH2]/MOTOR #2/WRG FAULT

Message Code:

27662322SX

Associated CAS:

CONFIG STAB TRIM
(Warning)

STAB TRIM
(Caution)

STAB CH2 FAIL
(Advisory)

There is a problem related to:

• Motor Drive Unit (MDU) fault bit status failure
• Failure detected during the flight control units Built-In Test on power-up with all the hydraulics systems pressurized caused by incorrect velocity feedback or brake hold test current feedback failure
• Horizontal Stab Trim (HST) Motor-Brake coil failure

• Pitch Trim Actuator Motor Drive Unit (MDU) (A184)
• Pitch-Trim Actuator (B44)
• Flight Control Unit (FCU) 2 (A66)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

NOTES:

• This fault may sometime be cleared by performing the flight control system reset procedure. If the message comes back more then once within 10 flight legs, troubleshooting is required.
• The status of the of the pitch trim system can verify in CAIMS:

1. SYSTEM DIAG
2. 27-00 FLIGHT CONTROLS
3. FLIGHT CONTROL UNIT #2
4. LRU TEST
5. DISPLAY ADVANCED EFCS DATA
6. Go to page 5 of 8

1. Interchange FCUs. Is the fault still present?

   1. If YES, continue with next step.
   2. If NO, replace defective FCU.
      NOTE: Make sure the FCU's are going through the complete Built-In Test with all hydraulic systems pressurized and wait 30 seconds after the 'SPLRS STAB IN TEST' CAS message clears.

2. If Ground Support Equipment 27X-41-09 MDU INVERTING HARNESS is available, interchange MDU channel to isolate the fault to the MDU or pitch trim Actuator motor.

   1. If faulty component was identified, make sure wiring is checked before replacing components.
   2. If GSE is not available, continue with next step.

3. Perform wiring checks between MDU (A184)  and FCU 2 (A66).

   From	To	Result
   A184P7-37	A66DP1-3H
   A184P7-23	A66DP1-3J
   A184P7-6	A66DP1-6G
   A184P7-7	A66DP1-5K
   A184P7-8	A66DP1-5J
   A184P7-24	A66DP1-3G

   1. If wiring defects are found, repair defective wiring as required.
   2. If no defects are found, continue with next step.

4. Interchange pitch trim actuators. Is the fault still present?

   1. If NO, replace pitch trim actuator motor 1 and do close out.
   2. If YES, continue with next step

5. Perform wiring checks between the MDU (A184) and the HSTA (B44) as follows:
   

   From	To	Result
   A184P6-A	B44P3-A
   A184P6-B	B44P3-B
   A184P6-C	B44P3-C
   A184P7-1	B44P4-34
   A184P7-3	B44P4-12
   A184P7-4	B44P4-11
   A184P7-10	B44P4-32
   A184P7-25	B44P4-33
   A184P7-19	B44P4-14
   A184P7-20	B44P4-13

6. Perform wiring check between the FCU 2 (A66) and HSTA (B44)

7. From	To	Result
   A66EP1-14J	B44P4-8
   A66EP1-15J	B44P4-9
   A66BP1-14C	B44P4-6
   A66BP1-15C	B44P4-5

   NOTE: Make sure wiring is checked for short circuit to ground or shield. If high resistance is measured, check all disconnects along the line for bent, damaged or unlocked pins.

   1. If defects are found, repair defective wiring as required.
   2. If no defects are found, continue with next step.

8. Replace the MDU. and do close out.