As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DESCENDING TROUGH FL310 CREW HEARD A VERY LOUD POP SOUND FOLLOWED IMMEDIATELY BY A STRONG SMOKE SMELL. NO SMOKE WAS OBSERVED, THE POP SOUND SEEMED TO COME FROM CABIN AREA. T/S FOUND AFT (COCKPIT) ACM INOP. GAINED ACCESS TO ACM. REMOVED ACM AND INSTALLED A REPAIRED ACM. REINSTALLED ACCESS ITEMS. OPS AND LEAK CHECK CHECKS GOOD. WORK DONE IAW MM 21-51-00.