As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE THE RIGHT MCDU SCREEN WENT DARK. THE FMC APPEARS TO BE OPERATING NORMALLY WHEN MAKING A CHANGE ON THE LEFT MCDU THAT REQUIRES AN EXECUTE, THE EXECUTE LIGHT DOES NOT ILLUMINATE ON THE RIGHT MCDU. WE SUSPECT THE MCDU IS INOPERABLE. GROUNDED - YES. REMOVED AND REPLACED FMCS CONTROL DISPLAY UNIT, REF B737-900 AMM 34-61-01. OPS CHECK PASSED, NO FAULTS NOTED AT THIS TIME. OKAY FOR SERVICE.