MD80 CREW TOOK OFF WITH THE DC BUS OFF LIGHT ILLUMINATED. THE CREW DID NOT MAKE A MAINT LOG DISCREPANCY OR CHK THE MEL.

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THE DC BUS OFF LIGHT REMAINED ON AFTER ENGS WERE STARTED. THE DC BUS OFF CHKLIST WAS ACCOMPLISHED. THE DC LOADS AND VOLTAGES WERE NORMAL. THE DC BUS SENSING CIRCUIT BREAKER WAS CHKED/RESET AND THE LIGHT REMAINED ILLUMINATED. IF THIS OCCURS THE CHKLIST STATES 'DISREGARD SINCE THE BUS IS PWRED AS INDICATED BY DC LOADS AND BUS VOLTAGES.' I DID JUST THAT. THE LOADS AND VOLTAGES WERE MONITORED ON THE LEG TO DFW AND THE TRIP WAS UNEVENTFUL. MAINT MET THE ACFT AND LOOKED AT THE BOOK. NOTHING WAS SAID TO ME; BUT THE MAINT MAN TOLD THE OUTBOUND CAPT HE THOUGHT THE ACFT SHOULD HAVE GONE BACK TO THE GATE AT PHL FOR REPAIRS SINCE THE ITEM WAS NOT CREW PLACARDABLE. UNFORTUNATELY; WHEN THE CHKLIST SAID; 'DISREGARD;' I DID NOT CHK THE MEL. I JUST ASSUMED THAT THE ACFT WAS OKAY TO FLY ESPECIALLY SINCE IT DID NOT HAVE AN 'IF INFLT OR IF ON THE GND;' SECTION LIKE THE BATTERY CHARGER LIGHT CHKLIST. IF MAINT IS CORRECT; THE DC BUS OFF CHKLIST SHOULD BE CHANGED TO REFLECT THAT INFO. THE WORD 'DISREGARD' ALSO NEEDS TO BE CHANGED OR REMOVED.