As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT FO'S FMC CDU BLANKED OUT FOR APPROX 17 SECONDS, DISPLAYED A "BIT TEST", THEN RETURNED TO NORMAL OPERATION. THIS SEQUENCE REPEATED APPROX EVERY ONE MINUTE. GROUNDED - YES. AIR TURNBACK - DIVERSION TIME 31 MINUTES - FOUND INFLIGHT FAULT FOR FO'S MCDU- REPLACED FO'S MCDU REF AMM 34-61-01-802 OPS CK OK. ETOPS GROUND VERIFICATION ACCOMPLISHED.