What was found
PDX FLIGHT NR 2229: AFTER TAKEOFF FROM SEA, RIGHT MAIN GEAR DOOR CAUTION LIGHT ILLUMINATED. STAYED ON ALL THE WAY TO PDX. DID NOT EXCEED 185 KTS. PERFORMED ALTERNATE GEAR EXTENSION. MAINTENANCE C/W OPERATIONAL TEST OF PRIMARY EXTENSION AND RETRACTION SYSTEM IAW Q400 AMM TASK 32-31-00-710-801. ALL GEAR DOORS OPERATED NORMALLY AND ALL LANDING GEAR INDICATIONS WERE NORMAL. INTERROGATED PSEU AND FOUND FAULT 'DIN01A UNREASONABLE FALSE'. REMOVED AND REPLACED LANDING GEAR SELECTOR PANEL. FUNCTIONAL CHECK OF PANEL WAS GOOD. NO DEFECTS NOTED AFTER NUMEROUS CYCLES OF LANDING GEAR EXTENSION RETRACTION. OPS CHECK FLIGHT PERFORMED. AIRCRAFT RETURNED TO SERVICE.