What was found
ON CLIMBOUT WITH FLAPS 8 DEGREES, STAB AND MACH TRIM WOULDN`T REMAIN ENGAGED. COMPLIED WITH QRH, RE-ENGAGED STAB AND MACH TRIM, BOTH DISENGAGED AND WOULDN`T REENGAGE. SET FLAPS TO 2- DEGREES, RETURNED TO DEPARTURE. REMOVED AND REPLACED FO`S HORIZONTAL STAB TRIM SWITCH IAW AMM 27-14-05, NO FIX. REMOVED AND REPLACED HSTCU IAW AMM 27-41-01. OPS CHECK GOOD, IAW AMM 27-40-00. (K)