What was found
(CAN) ON ARRIVAL , APU WAS IN OPERATION WHEN CREW SELECTED APU GENERATOR AND BLEED THERE WAS A BURNING ELECTRICAL SMELL, GPU WAS HOOKED UP BUT FAILED SHORTLY THEREAFTER , CREW THEN NOTICED A BLUISH HAZE THROUGHOUT THE CABIN AND THE BURNING SMELL WAS STRONGER....EMERGENCY SERVICES WERE CALLED OUT AND FIRE DID A COMPLETE SWEEP OF THE AIRCRAFT... PAX HAD ALREADY BEEN DEPLANED WHEN INCIDENT HAPPENED. REMOVED & REPLACED EXTERNAL POWER MODULE IAW AMM 24-42-01 OPS CHECK GOOD.