As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 5122 - CMH-MDW - IN FLIGHT, THE CREW RECEIVED A MACH TRIM EICAS MESSAGE. THE AIRCRAFT RETURNED TO THE FIELD WHERE MAINTENANCE REPLACED THE HSTCU AND A TEST FLIGHT WAS PERFORMED. THE TET FLIGHT WAS SATISFACTORY AND THE A/C WAS RETURNED TO SERVICE WITHOUT ANY FURTHR DISCREPANCIES.