As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER TAKEOFF, LANDING GEAR SELECTOR LEVER SELECTED UP, BOTH LT AND RT MAIN GEAR DOOR CAUTION LIGHTS ILLUMINATED, BOTH MAIN GEARS FAILED TO RETRACT BUT NOSE GEAR HAD RETRACTED. AC RETURNED TO BASE FOR FURTHER INVESTIGATION. FLIGHT SNAG COULD BE DUPLICATED ON GROUND. DURING TROUBLESHOOTING AND REMOVAL OF THE MLG SELECTOR VALVE, IT WAS NOTICED THAT FILTER HAD SEPARATED IN VALVE CAUSING BLOCKAGE. (TC NR 20071219001)