What was found
ON TAKEOFF AT POSITIVE RATE, MOVED THE GEAR LEVER TO THE UP POSITION . ALL GEAR LIGHTS EXTINGUISHED EXCEPT THE N. DOOR AMBER LIGHT. IMMEDIATELY AFTER THAT, THE LDG GEAR INOP CAUTION LIGHT ILLUMINATED. WE PROCCEEDED WITH CLIMB UP TO 12,000 FT AND REMAINED BELOW 200 KTS. RAN LDG GEAR INOP CAUTION CHECKLIST. RAN ALTERNATE GEAR EXTENSION CHECKLIST. DURING ALTERNATE GEAR EXTENSION CHECKLIST , ALL THREE GREEN LIGHTS ILLUMINATED UPON MOVING THE GEAR SELECTION HANDLE TO THE DOWN POSITION. CONTINUED FLIGHT WITH GEAR DOWN. LANDING UNEVENTFUL. REMOVED FROM SERVICE. REMOVED AND REPLACED PSEU DUE TO MULTIPLE INTERNAL POWER FAIL FAULTS AND CARD C FAULTS. OPS TEST OF LANDING GEAR SYSTEM GOOD . RETURNED TO SERVICE.