What was found
ON FLIGHT 2866 THE CREW REPORTED THAT ON THE TAKEOFF ROLL AT ABOUT 80 KTS RECEIVED A MASTER WARNING TRIPLE CHIME "TRIM" MESSAGE. AT THAT TIME A ROLL TRIM BOX ON EICAS APPEARED. WHEN THE NUMBERS ON TRIM BLOCK RE-APPEARED THE TRIM WENT FROM 8 TO 6. TRIM SWITCH WAS NOT TOUCHED DURING TAKEOFF ROLL. LOW SPEED ABORT. THE AIRCRAFT WAS REMOVED FROM SERVICE. REMOVED AND REPLACED HORIZONTIAL STAB CONTROL UNIT IAW EMB 140 AMM 27-40-01. THE OPERATIONAL CHECK WAS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE.