What was found
PITCH TRIM FAIL. R&R HS-ACE PER MM 27-43-01. HSACE WAS CONFIRMED TO HAVE HAD A DUAL CHANNEL FAILURE WHICH CASED THE HORIZONTAL STAB PITCH TRIM TO REMAIN IN THE LAST POSITION COMMANDED PRIOR TO THE HSACE FAILURE. RESULTED IN FLIGHT CREW UNABLE TO MOVE STAB PITCH TRIM, AIRCRAFT WAS CONTROLLABLE WITH PILOT INPUT TO ELEVATOR CONTROLS. DECLARED AN EMERGENCY, DIVERTED, AND LANDED WITHOUT FURTHER INCIDENT. EVALUATION CONFIRMED A DUAL CHANNEL FAILURE CAUSED BY MOSFETS INSTALLED ON PC BOARD 548-261-001 INTERNAL TO THE HSACE.