What was found
FLT 561, PUJ-ORD, ON APPROACH THE FLAPS WOULD NOT EXTEND FROM ZERO POSITION. SLATS EXTENDED NORMALLY (ECAM FLAP FAULT WHEN FLAPS 2 SELECTED). ECAM WERE ACTIONS FOLLOWED, AND FCOM & QRH WERE CONSULTED, AND IT WAS NECESSARY TO PREPARE & BRIEF FOR A ZERO FLAP APPROACH. THE CAPT DECLARED AN EMERGENCY & HAD THE FIRE/RESCUE VEHICLES STANDBY. THE APPROACH WAS MADE IN ACCORDANCE WITH THE QRH WITH NECESSARY ADJUSTMENTS TO CONFIGURATION & SPEED. LANDING WAS UNEVENTFUL. MAINTENANCE C/W TSM 27-51-00-810-803 & OPS CK'D FLAP SYS OK, & FOUND NO TORQUE LIMITERS TRIPPED. FOUND FLAP CONTROL UNIT ASSY TO GET JAMMED/STICKING BETWEEN 0 AND 1 DETENT. REMOVED AND REPLACED FLAP CONTROL UNIT ASSY PER AMM 27-51-43PB401 & OP'S CHECKED OK. AIRCRAFT RETURNED TO SERVICE.