What was found
AIRCRAFT WAS GROUNDED, AN EMERGENCY WAS DECLARED DUE TO: RIGHT AFTER TAKE OFF AUTO FAIL ON CABAIN PRESSURE CONTROLLER IN BOTH AUTO AND ALTERNATE MODE; AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT DFW. FOUND CB: F5 "AUTO 2" (FO P6-4 PANEL) PULLED AND COLLARED. REMOVED COLLAR AND PUSHED IN CB. PERFORMED PRESSURIZATION GROUND TEST PER AMM 21-31-00. BOTH CABIAN PRESSURE CONTROLLER 1 AND 2 TEST PASSED. HOWEVER DUE TO AIR TURN BACK, REMOVE AND REPLACED CABIAN PRESSURE CONTROLLER 1, PER AMM 21-31-01. OPERTIONAL CHECK GOOD.