What was found
WHILE IN CRUISE @ FL340 VTK ON CAPTAINS ND ILLUMINATED FOLLOWED BY BOTH MCDU'S GOING BLANK (MENU) WITH A/T LIM ANNUNCIATION. CAPTAINS MAGENTA LINE ALSO DISAPPEARED ON CAPTAINS ND. ALL SYSTEMS RESTORED WITHIN 15 SECONDS BEFORE QRH COULD BE ACCOMPLISHED. GROUNDED - YES. INBOUND FLT LOGGED NO FMC-1 INPUT FAULT 34-69001 PERFORMED B737-9 IFIM TASK 34-61-00-810-836 AND NO CURRENT FAULTS FOR L/H FMC GROUND VERIFICATION CK OF L/H FMC PASSED REF B737-9 AMM 34-61-00/710-801.