What was found
PERFORMED GROUND AIR START DUE TO DEFERRED APU DIRTY SOCK ODOR. ONCE THE NR 2 ENGINE WAS STARTED, THE DIRTY SOCK ODOR RETURNED IMMEDIATELY. PERFORMED A CROSS BLEED START. THE ODOR CONTINUED. ODOR APPARENT THROUGHOUT THE WHOLE OF THE AIRPLANE, BUT FLIGHT ATTENDANTS REPORTED THAT IT WAS WORST TOWARDS THE AFT SECTION. COMPLIED WITH INFORMATION NOTICE 2017-T015A, SECTION B, AIRCRAFT IS OK FOR SERVICE. THE SOURCE OF THE ODOR WAS ISOLATED TO THE APU BLEED. R & R APU GENERATOR IAW AMM 24-23-51. LEAK CHECKED OK, NO DIRTY ODOR NOTED WHILE APU ON.