What was found
10 MIN INTO FLT, AFT AVIONICS COMPARTMENT, RACK POWER WARNING , LIGHT IN BUTTON AND HORN . TURNED POWER OFF, NO FURTHER WARNING. LEFT IN OFF POSITION FOR REST OF FLT. REMOVED AND REPLACED COOLING FAN ASSY IAW MM 23-39-00. LTV OPS CK GOOD IAW LTV MM 23-39-00.