As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED SMOKE IN CABIN, FOLLOWED BY A POP, THEN BURNING ODOR. ODOR AND SMOKE DISAPATED WHEN NR 2 PACK WAS DESELECTED. ACFT PERFORMED AN AIR RETURN WITHOUT INCIDENT. INSPECTED AND FOUND NR 2 PACK TO BE INOPERATIVE. NR 2 AIR CYCLE MACHINE WAS R & R WITH OPS CHECK GOOD. ACFT WAS APPROVED FOR RETURN TO SERVICE.