What was found
(CAN) THE LANDING GEAR HAD A SERIES OF 2 FAILURES WHERE THE 60 AMP BREAKER TRIPPED AS THE MLG WAS RETRACTING & WOULD NOT RESET THEREBY FORCING THE CREW TO LOWER THE GEAR WITH THE EMERGENCY SYS & RETURN TO BASE. THE FAILURE COULD NOT BE DUPLICATED WHEN THE GEAR WAS SWUNG BY MAINT. THE HYD DRIVE MOTOR WAS BENCH CHECKED OK & BREAKER REPLACED. A THIRD INCIDENT WHERE BREAKER TRIPPED WHILE THE A/C WAS STILL ON THE RAMP PROMPTED MAINT TO CARRY OUT A FULL 1000 HR SYS INSPECTION DURING WHICH THE THERMAL RELIEF VALVE WAS DISCOVERED TO OPEN AT RANDOM CAUSING THE HYD PUMP TO CYCLE RAPIDLY UNTIL CIRCUIT HEATED UP & THE BREAKER TRIPPED. IT WAS REPALCED WITH AN OVERHAULED VALVE AND THE A/C RETURNED TO SERVICE.