What was found
PHX - SMOKE - FLT 0052 - EN ROUTE FROM SJD TO PHX FLIGHT CREW NOTICED SMOKE EMANATING FROM BOOM / OXYGEN SWITCH ON NR 2 AUDIO SELECTOR PANEL, SMOKE STOPPED SHORTLY AFTER IT WAS NOTICED. MAINTENANCE REMOVED AND REPLACED THE NR 2 AUDIO SELECTOR PANEL IAW BMM 23-51-01, OPERATIONAL CHECK WAS GOOD. VENDORS SHOP EVALUATION OF AUDIO SELECTOR PANEL S/N D00410 CONFIRMED REASON FOR REMOVAL FINDING RESISTOR (R1) AND CAPACITOR (C1) ON A2 CIRCUIT BOARD BURNED. REPLACED RESISTOR (R1) AND CAPACITOR (C1) ON A2 CIRCUIT BOARD, AND REPLACED OXYGEN / BOOM SWITCH PER E.O. 2350 01001. UNIT CLEANED, INSPECTED, AND TESTED IAW CMM 23-51-54, REV. 27.