What was found
(CAN)ON TAKEOFF MASTER CAUTION LIGHT CAME ON WITH LEFT AC BUS OFF, GENERATOR OFF, DC BUS OFF LIGHT ON, AC X TIE LOCKOUT LIGHT ON. LEFT CSD OIL PRESSURE LOW LIGHT ON, CSD DISCONNECTED AND AIRCRAFT RETURNED TO BASE. MAINTENANCE INVESTIGATION REVEALED SCAVENGE FILTER HOUSING BROKEN ON LEFT CSD. LEFT CSD P/N 696233A, GENERATOR, CSD OIL COOLER REPLACED AND GROUND RUN CARRIED OUT.