What was found
INVESTIGATED PILOT COMPLAINT OF FAILED HORIZONTAL STABILIZER DEICE SYSTEM, FAIL INDICATION. REQUIRED REPLACEMENT OF HORIZONTAL STAB. DEICE SYSTEM MOSFET CONTACTORS K251, K252, K253, K254 TO RECTIFY AND OBTAIN SUCCESSFUL OPERATIONAL TEST. FAILED UNITS SHOWED VARIOUS INTERNAL FAULTS. PN 1283840545 UNITS (MFG PN 114192) HAVE BEEN SUPERSEDED BY PN 128-384054-7 (MFG PN 11419-3); RELIABILITY MAY BE IMPROVED OVER THE -5 UNITS. MOSFET CONTACTORS ARE FOUND TO FREQUENTLY BE THE SOURCE OF FAILED HORIZONTAL STABILIZER DEICE SYSTEM FAILURES. PART TT SINCE NEW/ REPAIRED UNKNOWN. AIRCRAFT TT 3336.1 HOURS/ 2693 CYCLES.