What was found
ON TAKEOFF, PILOT SELECTED MLG UP, A HYD CAUTION & WARNING SYS LAMP, MASTER CAUTION & AURAL GONG ACTIVATED. MLG SELECTED DOWN NO CHANGE OBSERVED & MLG SELECTED UP NO CHANGE OBSERVED. HYD C/B PULLED. INDICATION OF A RED NLG LIGHT & GREEN MLG LIGHTS. PILOT FLEW ACFT BACK TO MAIN BASE, WITH MLG DOWN. ON APPROACH, MLG SELECTED DOWN & EMERGENCY GEAR HANDLE WAS USED TO APPLY DOWN PRESSURE & TO CONFIRM THAT THERE WAS HYD PRESS. ALL 3 GREEN MLG LIGHTS ILLUMINATED. ACFT DID A LOW FLY OVER TO CONFIRM DOWN. LANDING UNEVENTFULL. HYD POWER RELAY FOUND FAILED. HYD POWER RELAY REPLACED. MLG RETRACTION & EXTENTION TEST PERFORMED, NO DEFECTS. ACFT RETURNED TO SERVICE.