What was found
ON FLIGHT 3850 (MEM TO PIT) PERFORMED AN AIR TURNBACK TO MEM FOR FLAP FAIL AT 20 DEGREES. FAILED WHILE TRYING TO BRING FLAPS FROM 20 TO 0 AFTER TAKEOFF. PERFORMED TROUBLESHOOTING PER BOMBARDIER FIM REV 44 IAW AD 2009-06-12 PARAGRAPH (H)(6)(I), AMOC DATED DECEMBER 07 2012, AND PA AD27-052J. TROUBLESHOT FLAPS FAIL PER FIM 27-50-00. LRU LOG RIGHT BPSU INDICATES FAULT CODES 51A 52A 121B 122B. REMOVED AND REPLACED RIGHT BPSU IAW AMM 27-51-10. PERFORMED RIGGING OF FLAPS IAW AMM 27-51-01. OPERATIONS CHECK GOOD. OK FOR SERVICE. MOD BB APPROVED TS 52812.