IS UNSERVICEABLE AND CANNOT BE REPAIRED OR REPLACED WITH THE SAME PART NUMBER. VENDOR SERVICE BULLETIN MOS INDICATING/RECORDING SYSTEMS- PHASE 3 DISPLAY UNIT - MODIFICATION (MOD) C TO PHASE 3 DISPLAY UNIT. PN RECOMMENDED 4091900-931 THRU -934. -941 THRU -944: IMPROVE DISPLAY UNIT CONTROLLER (DUC) SEQUENCER FIRMWARE IN