What was found
ON T/O AFTER FLAPS WERE SELECTED TO 0 DEG FLAP DRIVE CAUTION LT ILLUMINATED. FLAPS INDICATED 0 DEG AND FLAP SELECTOR LEVER INDICATED 0 DEG LANDING WAS ACCOMPLISHED AT FLAP 0 DEG PER E/A CHECKLIST. RETURNED TO FIELD. EMERGENCY DECLARED. LANDING UNEVENTFUL. REMOVED FROM SERVICE. NO FAULTS IN CDS. PERFORMED OPS TEST OF FLAPS IAW AMM 27-50-00-710-801. TEST FAIL. "FLAP DRIVE" CAUTION ILLUMINATES WHENEVER FLAPS ARE NOT MOVING. REMOVED FPU IAW AMM 27-52-01-000-801. MW 63463 9/12/19. REPLACED FPU IAW AMM 27-52-01-400-801. FUNCTIONAL TEST GOOD. NO FAULTS FOUND IN CDS. FLAP DRIVE CAUTION LIGHT NOT ILLUMINATED. LEAK CHECK GOOD. NO FURTHER ACTION. AIRCRAFT RETURNED TO SERVICE.