What was found
ABL - FLT 501 - AFTER T/O AT 8,000 FEET, NR 2 T/R C/B TRIPPED. (BLOWER NORMAL, NR 1 BUS T/R). CABIN STARTED TO CLIMB AT 2,000 FEET/MIN. DOOR ANNUNCIATOR 'AFT CARGO PIT' WARNING LIGHT CAME ON. PILOT RETURNED TO ALB. MECH RESET C/B'S, RAN NR 1 ENG AND LOADED GEN. C/B FOR NR 1 T/R TRIPPED AGAIN. SECURED NR 1 GEN AND PUT APU ON LINE; LOADED UP SYS ELECTRICALLY AND PROBLEM DID NOT RETURN. THIS INDICATED NR 1 GEN FAILED. VERIFIED APU HAS FUEL HEATER AND DEFERRED NR 1 ENG GEN (MEL 24-1). AFT CARGO PIT WARNING SYS WAS INDICATION PROBLEM ONLY; ITEM DEFERRED (MEL 52-3). DOOR VERIFIED CLOSED AND LOCKED. REMOVED AND REPLACED NR 1 GEN AND DOOR WARNING ANNUNC. CLEARED MEL. REF: OPER CNTRL NR ZZDA2424497.