What was found
THE RADAR WILL NOT PAINT THUNDERSTORMS AT CRUISE, WHICH VISUALLY CONFIRMED TO EXTEND ABOVE OUR ALTITUDE. FURTHER , NO GROUND RETURNS ARE PRESENT WHEN "GC" IS PUSHED. THIS ALL IN AUTO MODE. SWITCHED TO MANUAL MODE. ANTENNA APPEARS TO BE MISSALIGNED BY 3 TO 4 DEGREES. EG, WHEN "O" TILT IS INDICATED, ANTENNA IS ACTUALLY +3. THIS RESULTS IN BEAM OVER SCANNING CONVECTIVE WEATHER - I.E. EITHER DON'T APPEAR ON DISPLAY OR ARE EXTREMELY WEAK RETURNS. ACFT GROUNDED. REPLACED WEATHER RADAR ANTENNA DRIVE UNIT, OPS NML REF MM 34-43-11-400-802 AND MM 34-43-00-710-802-001.