What was found
(CAN) AC DEPARTED BASE AND UPON GEAR RETRACTION BOTH LT AND RT HYD PRESSURE LIGHTS ILLUMINATED FOR 3-4 SECONDS THEN WENT OUT. AIRCRAFT RETURNED TO BASE AND UPON INVESTIGATION IT WAS FOUND THAT NO RESIDUAL HYD PRESSURE WAS PRESENT AFTER ENGINE SHUTDOWN. UPON FURTHER INVESTIGATION IT WAS DISCOVERED THAT THE 31 PSI REGULATOR WAS CONTAMINATED WITH HYD FLUID. THE REGULATOR CHECK VALVE HAD BEEN INSTALLED INCORRECTLY. THE CHECK VALVE WAS REPOSITIONED AND THE REGULATOR WAS REPLACED. GEAR WINGS WERE CARRIED OUT SERVICEABLE AND AIRCRAFT RETURNED TO SERVICE. (TC NR 20070307009)