As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, CREW RECEIVED A NR 2 PACK 2 OVERLOAD AMBER CAS MESSAGE. FLIGHT ATTENDANT HEARD A LOUD BANG AND SMELLED ELECTRICAL SMOKE. CREW RETURNED TO DEPARTURE AND LANDED WITHOUT INCIDENT. MAINTENANCE REPORTED THE RIGHT AIR CYCLE MACHINE HAD FAILED. THE ACM WAS REPLACED.