What was found
AIRCRAFT NOT GROUNDED: PILOT REPORTS DURING DEPARTURE WHILE LEVEL AT 10,000. FMC REVERTED TO HDG MODE. RE-ENGAGED NAV, DROPPED BACK TO HDG MODE AGAIN DURING CLIMB TO 17,000. RE-ENAGED NAV AGAIN AND RECEIVED UNCOMMANDED TURN TO THE RIGHT MCDU SCRATCH PAD SHOWED FM PREDICTIONS LOST MESSAGE. RE-ENGANGED NAV A THIRD TIME AND ALL OPS NORMAL. MAINTENANCE PERFORMED POST FLIGHT REPORT FAIL MSG. MMR1 GPSSU1 T/S IAW TSM 34-14-00. FOUND #1 MMR AT FAULT. REPLACED MMR #1 IAW AMM 34-36-31. OPS AND BITE CHECKS NORMAL. RETURN TO SERVICE PROCEDURE PASSED IAW AMM 22-97-00.