What was found
AUTO FAIL LIGHT ILLUMINATED ON CABIN ALTITUDE CONTROL PANEL WITH ALTERNATE (GREEN) LIGHT ALSO ILLUMINATED, NO NOTICABLE PRESSURE CHANGES. FOLLOWED QRH AND SELECTED ALTERNATE POSITION ON CONTROL PANEL, PRESSURE OPERATES NORMALLY, NOTE: SLIGHT DUCT SPLIT. LT DUCT PRESSURE=31, RT DUCT PRESSURE= 43. ACFT GROUNDED. NO FAULTS ON NR 1 CONT, NR 2 CONTROLLER FAULTED OF LRU, CLEARED FAULT. RAN SYS GROUND TEST 2XS ON PRESS CONT NR 2 BOTH XS TEST PASSES. RETURN PANEL TO AUTO, REF MM 21-31-00-700-802. NO AUTO PRESS HISTORY. THE IN-FLIGHT DUCT PRESSURE SPLIT IS LESS THAN 20 PSIG NO FURTHER ACTION IS REQUIRED, DUCT SPLIT IS WITHIN LIMITS REF MM 36-11-00 STEP 1. I (1).