What was found
AIR TURNBACK - FLT 704 - DURING CLIMBOUT OF PHX THE AUTO PILOT DISCONNECTED, YAW DAMPER DISENGAGED AND B-SYSTEM HYDRAULIC PRESSURE WENT TO ZERO. AT THE TIME OF OCCURRENCE THE NR 2 B-SYSTEM ELEC HYD PUMP WAS INOPERATIVE ON MEL 29-2 COND 1 DUE TO LOW PRESSURE. THE AIRCRAFT WAS RETURNED TO PHX AND MADE AN UNEVENTFUL LANDING. IN PHX MAINTENANCE REPLACED THE NR 2 B-SYS HYD PUMP WHICH WAS NO HELP. FURTHER TROUBLESHOOTING DETERMINED THE B-SYSTEM HYDRAULIC MODULAR PACKAGE ASSY TO BE THE CAUSE FOR LOSING PRESSURE. THE B-SYS HYD MOD ASSY WAS REPLACED PER AMM 29-12-31 AND OPERATIONAL AND FUNCTION CHECKS WERE GOOD. MEL 29-2 WAS CLEARED. NO FURTHER DISCREPANCIES HAVE BEEN REPORTED.