What was found
FALSE RADAR RETURNS APPEARING ON CAPTAIN'S RADAR. F/O'S RADAR DOESN'T SHOW SAME RETURNS. GROUNDED - YES. ONLY CAPTAIN'S SIDE REPORTED AT FAULT, NOT F/O'S SIDE. RADAR SYSTEM CHECKED GOOD ON GROUND IAW B737-800 AMM 34-43-00-710-802. PERFORMED DEU #1 BITE CHECK IAW AMM 31-62-00/501, OPS CHECK GOOD. GROUND FUNCTIONAL CHECK ETOPS CHECK FOR RADAR SYSTEM GOOD IAW AMM 34-43-00-710-802. RE-RACKED DEU #1 AS PART OF RESETTING SYSTEM. LLLM TEST FOR DEU GOOD IAW AMM LRU REPLACEMENT TEST 22-11 TASK 802. AIRCRAFT REMAINS AUTOLAND AND HGS CAT III QUALIFIED. DEU #1 AND CAPTAIN'S RADAR DISPLAY CURRENTLY WORKING IAW AMM 31-62-00/501 AND 34-43-00.