Horizontal Stabilizer Motor Drive Unit reported a loss of AC power going to Motor Drive Unit (MDU) Channel 1 or a failure of the internal power supply.

• AC Power Center (ACPC) (A54)
• Pitch Trim Actuator Motor Drive Unit (MDU) (A184)
• Associated Wiring

Advisory Wire/Service Bulletin: None

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

Flight Operation Notifications Manual (FONM): None

NOTES:

• This fault is posted when the following thermal breaker is pulled.
  

  Location	CB No.	Name
  ACPC	B6	STAB TRIM CH 1

• 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, perform the following troubleshooting.
• Verify C/B status on both pilot and copilot EMS CDUs. This CAS Message will post if either of the following circuit breaker or Smart Contactor status is OUT or Tripped.
  

  LOCATION	CB No.	NAME
  ACPC (A54)	CB-B6	STAB TRIM CH1
  ACPC (A54)	SC-K15	AC 1 FEED

1. Check status of AC 1 FEED on EMS CDU, the AC 1 Feed being out or tripped can drive multiple CAS to post.
   BUS > AC 1 > AC 1 FEED.

   1. If AC 1 FEED CB is IN go to step 3.
   2. If AC 1 FEED CB is OUT, set to IN.
      

      AC 1 FEED

      CB	SYSTEM	PHASE	CAS
      CB-G6	ESS TRU 1	3	AC BUS 1 FAIL (Caution)
      CB-G3	EVS FAIRING HEAT	3	EVS HEAT FAIL (Caution)
      CB-G9	SLAT/FLAP PWR 1	3	SLAT-FLAP HALFSPD (Advisory)
      CB-H5	EVS WINDOW HEAT	1	EVS HEAT FAIL (Caution)
      CB-H6	A/T CTLR	1	A/T 1 FAIL (Advisory) A/T 2 FAIL (Advisory)
      CB-H7	PITOT 1 HT A	1	PITOT 1 HT FAIL (Caution)
      CB-H8	R ICE DETECTOR	1	ICE DETECTOR FAULT (Advisory)
      CB-H9	R AOA HEAT A	1	R AOA HEAT FAIL (Caution)
      CB-H10	L WSHLD HEAT 1	1	L WSHLD HEAT FAIL (Caution)
      CB-H11	L WSHLD HEAT 2	1	R WSHLD HEAT FAIL (Caution)
      CB-H12	TRU BAY FAN	3	ELEC SYS FAULT (Advisory)
      CB-B6	STAB TRIM CH1	3	STAB CH 1 FAIL (Advisory)

2. Did the CAIMS Fault & CAS messages clear after setting AC 1 FEED CB to IN.

   1. If YES, do close out.
   2. If NO, go to next step.

3. Check status of STAB TRIM CH 1 Non-Thermal Circuit Breaker (CB-B6).

   1. If circuit breaker is tripped, go to step 5.
   2. If circuit breaker did not trip, continue with next step.

4. Perform voltage checks between MDU connector A184P1 to aircraft ground as follow:

   From	To	Expected Result	Result
   A184P1-A	Ground	115 VAC
   A184P1-B	Ground	115 VAC
   A184P1-C	Ground	115 VAC

   1. If checks are good, go to step 6.
   2. If any of check fails, continue with next step.

5. Disconnect the connector A184P1 and reset the CB. If the CB trip again. Perform wiring checks between MDU and ACPC.

   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.

6. Use the Ground support Equipment 27X-41-09 "MDU INVERTING HARNESS" to confirm the fault, prior to replacing any units.
   

   1. If the fault is isolated to the MDU, replace the MDU and do close out.
   2. If the fault is isolated to the HSTA, continue with the next step

7. Replace HSTA, do close out.
   NOTE: The Pitch Trim Motors can be interchanged for confirmation before replacing a component.
8. Do close out.

NOTE: The MDU status can be verified via CAIMS.

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