What was found
FLT 1986, PIT-BOS. EMERGENCY DECLARED. RETURNED TO FIELD. SMOKE IN COCKPIT AND CABIN AT FL 190 PERFORMED FULL QRH PROCEDURE IMMEDIATE RETURN TO FIELD. ALL ASSOCIATED EQUIPMENT USED INCLUDING COCKPIT O2, RAT, ETC; ACCOMPLISHED FIM TASK 21-20-00 FOUND #1 ACM TO BE BE AT FAULT.