What was found
PILOT WRITE UP, DURING CRUISE FLIGHT L MFD (DU) DIMMED AND COULD NOT BE ADJUSTED BRIGHTER. ALSO AN ACRID SMELL WAS NOTABLE IN A/C. NO WARNING LIGHTS ILLUMINATED. AT BASE REMOVED DISPLAY UNIT FROM INSTRUMENT PANEL AND INSPECTED WIRES FOR ANY TYPE OF DAMAGE OR BURNT AREAS NO DEFECTS NOTED. TURNED POWER ON. EVERYTHING POWERED UP NORMALLY AND THE DISPLAY UNITS WERE BOTH THE SAME BRIGHTNESS. WITHIN A FEW SECONDS A SMOKE/BURNING LIKE SMELL CAME FROM THE LEFT, CENTER, DU. CALLED MCAS AND TOOK THE ACFT OUT OF SERVICE.