What was found
DURING CLIMB OUT, WHILE ACTIVATING MAIN PITCH TRIM SWITCH, ICAS WENT TO INOPERATIVE, THE MASTER WARNING WENT TO INOPERATIVE, THE MESSAGE REMAINED AFTER THE TRIM SWITCH WAS RELEASED.. MESSAGE ALSO REMAIN WAS RELEASED. ACFT RETURNED TO BASE AND MAINTENANCE RETRIEVED A CMC MESSAGE FOR THE HSCU FAIL WITH 1 OCCURRENCE ON 5-23. R & R THE HSCU IAW AMM 27-40-01. OPS CHECK GOOD.