What was found
FLAP FAIL YELLOW CAS: FLAP FAIL CAS MESSAGE WHEN THE FLAP HANDLE WAS MOVED TO THE FLAP 1 POSITION. THE FLAPS DID NOT EXTEND. WE WERE AT 170 KTS AND APPROXIMATELY 8,000' ON THE VISUAL APPROACH TO KSUN. REMOVED FAULTY FLAP PDU AND INSTALLED TESTED PDU IAW AMM 27-51-07. DISCONNECTED THE PDU FROM FLEX SHAFTS AND BROUGHT EACH FLAP PANEL IN TO THE ZERO POSITION AS REQUIRED TO CORRECT FLAP RIGGING DISCREPANCY IAW AMM MPP 27-50-00-820-801-A AND 27-50-00-720-801-A. ONCE FLAPS WERE VERIFIED IN THE PROPER RIGGED POSITION, ALL FLEX SHAFTS WERE RE-INSTALLED. PERFORMED ELECTRONIC RIGGING OF THE FLAPS REF AMM 27-50-00-720-801-A. PERFORMED FLAP FUNCTIONAL CHECK IAW AMM 27-50-00 WITH NO DEFECTS NOTED.