As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EWR INFLIGHT T1147/11SEP ACRID SMOKE IN CABIN IMMEDIATELY AFTER TAKEOFF. PACKS SHUT OFF AND LANDED EWR WITHOUT INCIDENT. REPLACED O-RING AT THERMOSTAT VALVE OF APU. PERFORMED PACK BURN OUT AND ENGINE HIGH POWER RUN UP WITH NO SMOKE NOTED. SYSTEM GROUND CHECKED NORMAL OPERATION.