What was found
APPROXIMATELY 150 NM FROM BASE, CRUISING AT FL 230, WHEN CO-PILOT NOTICED A SUDDEN PUFF OF SMOKE FROM BEHIND CAPTAIN'S SEAT. A LOUD BANG & PRIMARY & AUXILIARY INVERTER LIGHTS ILLUMINATED. ADDITIONAL WARNING LIGHTS ASSOCIATED WITH THESE FAILURES ALSO ILLUMINATED. OXYGEN DRILL CARRIED OUT FOLLOWED BY FUSELAGE FIRE OR SMOKE DRILL. IDENTIFIED PROBLEM AS PRIMARY INVERTER & AFTER COMPLETING THAT DRILL FROM QRH, AUX INVERTER RE-INSTATED. UNSCHEDULED LANDING CARRIED OUT. MX PERSONNEL INSPECTION A/C & PERFORMED TROUBLESHOOTING ON INVERTER SYS. FROM THIS, PRIMARY INVERTER CONFIRMED AT FAULT. PRIMARY INVERTER THEN REPLACED. AIRCRAFT HAS RETURNED TO SERVICE WITHOUT FUTHER INCIDENT.