What was found
(CAN) ON APPROACH, COCKPIT FILLED WITH SMOKE AS THE NR 1 GCU WAS FAILING. ALSO, NR 1 GENERATOR TRIPPED OFF-LINE AT THIS TIME. THE CABIN REMAINED SMOKE FREE DURING DESCENT AND LANDING. INSPECTION REVEALED THAT NR 1 GCU SMOKED, GCU REPLACED, BUT ON GROUND RUN, THE GCU SMOKED AGAIN. NR 1 GENERATOR AND GCU REPLACED, AIRCRAFT SERVICEABLE.