As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APPROACHING THE CRITICAL POINT, NR 1 CDU WENT COMPLETELY BLANK FOR 20 SECONDS. IT CAME BACK IN A BITE TEST MODE AND THEN RETURNED TO NORMAL FUNCTION. NO PILOT ACTIONS WERE TAKEN DURING THIS EVENT. ACFT GROUNDED. REMOVED LT FMC CDU REF 34-61-01. CLEANED COOLING VENT IAW 34-61-01. REINSTALLED LT FMC CDU 34-61-01. OPS CHECK REF 34-61-00-710-801. SYS CHECKED NORMAL.