What was found
PHX - AIR TURNBACK, EN ROUTE FROM PHX TO AUS THE WEATHER RADAR BECAME UNRELIABLE; EXCESSIVE TILT UP, 6 DEG TO ELIMINATE GROUND CLUTTER (CLIMB THRU 16000 FT) WINGS LEVEL RADAR POINTS IMAGES TO RIGHT, OCCASIONALLY LEFT EVEN WITH TILT 6 DEG; STABILIZATION OFF IMPROVES, BUT STILL UNRELIABLE; DUE TO WEATHER IN AUS THE AIRCRAFT RETURNED TO PHX. IN PHX THE PAX WERE PUT ON ANOTHER AIRCRAFT AND THE FLIGHT DEPARTED. THE RADAR WAS PLACED ON MEL 34-15 CONDITION 1 AND ROUTED ON A FLIGHT THAT DIDN''T REQUIRE ITS USE. ON 5/8/01 MAINTENANCE REPLACED THE RADAR RECIEVER/TRANSMITTER UNIT AND FUNCTIONALLY TESTED GOOD AND THE MEL WAS CLEARED.