What was found
PDX - GEAR WARNING HORN SOUNDED WHEN FLAPS WERE SELECTED TO FULL FROM HALF. GEAR WAS DOWN AND LOCKED. GEAR WARNING CIRCUIT BREAKER PULLED. AIRCRAFT LANDED WITHOUT FURTHER PROBLEM. CIRCUIT BREAKER WAS RESET AFTER THE AIRCRAFT WAS PARKED AND HORN DID NOT SOUND. RIGHT MAIN GEAR DOWN POSITION SWITCH WAS REPLACED AND ADJUSTED I/A/W MAINT. MANUAL. GEAR OPS CHECKED GOOD ON GEAR SWING. AIRCRAFT RETURNED TO SERVICE.