What was found
ON CLIMB OUT, APPROACHING 11000FT, THE ACFT EXPERIENCED A LOSS IN CABIN PRESSURE. THE CREW SWITCHED TO MANUAL MODE & WAS UNABLE TO PRESSURIZE THE ACFT. AN EMER DESCENT WAS COMPLETED TO 10000 FT & A RETURN INITIATED DUE TO THE DEPRESSURIZATION. NO EMER WAS DECLARED & THE ACFT LANDED WITHOUT FURTHER INCIDENT. PERFORMED A SELF-TEST ON AUTO CONTROLLER, INITIALLY IT PASSED, BUT THEN ON SECOND SELF-TEST DISPLAY WENT BLANK & UNIT FAULTED & DID NOT RESET. REPLACED THE DIGITAL AUTO CONTROLLER, OPERATIONS CHECKED GOOD. ACFT RETURNED TO SERVICE.