As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RADAR DOES NOT DEPICT THUNDERSTORMS, APPEARS TO HAVE LOW POWER OUT OR BAD RECEPTION AS ONLY PARTIAL RETURNS ARE DISPLAYED. IMPROVES SLIGHTLY WITH GAIN INCREASE BUT STILL UNSAT. GROUNDED - YES. REMOVED AND REPLACED WEATHER RADAR TRANSCEIVER. OPS CHECK NORMAL. B737-800 AMM 34-43-00.