What was found
AFTER TAKEOFF AT GEAR RETRACTION, NOSE GEAR LIGHT REMAINED GREEN AND NOSE GEAR DID NOT RETRACT, UNLOCK RED LIGHT ILLUMINATED MAINS OPERATED NORMALLY. IAW EMERGENCY CHECKLIST, EXTENDED GEAR AND 3 GREEN LIGHTS, NO UNLOCK RED. NOSE WHEEL STEERING UNIT WOULD NOT PASS GEAR UP CENTERING TEST. REMOVED & REPLACED NWS UNIT, RIGGED NWS UNIT, OPERATIONALLY CHECKED GOOD. IAW MM 32-50-00, & LEAK CHECKED GOOD.