As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT MCDU DISPLAY AT MAX BRIGHTNESS IS ONLY 1/2 AS BRIGHT AS THE RIGHT MCDU. NOTE: LEFT MCDU WENT TO FULL BRIGHT APPROX AFTER 2 HOURS AT CRUISE. GROUNDED - YES. COULD NOT DUPLICATE ISSUE. CAPTAIN'S MCDU OPS NML REF B737-9 MM 34-61-01. ETOPS GROUND VERIFICATION TEST SUCCESSFUL. SEAMC ETOPS JEREMY NOTIFIED.