What was found
THE AUDIO CONTROL PANEL EMITTED SMOKE AND STOPPED OPERATING DURING TAXI PRIOR TO FLIGHT. AIRCRAFT RETURNED TO BASE, MAINTENANCE REMOVED THE UNIT FROM AIRCRAFT AND VERIFIED AIRCRAFT BUS BAR VOLTAGE WITH ALTERNATOR OPERATING. A WORKING KMA-26 WAS INSTALLED, OPERATION WAS VERIFIED IAW MM AND AIRCRAFT WAS RETURNED TO SERVICE. THE AIRCRAFT/AUDIO CONTROL PANEL HAD NOT COMPLIED RECOMMEND MFG SB03-23-01 AND SB KMA26-5. THE BULLETINS REQUIRE THAT POWER MODULE INSIDE THE KMA-26 BY REPLACED WITH A UPDATED PART NUMBER. THE KMA-26 HAD BOARD TRACE DAMAGE, BELIEVED TO BE CAUSED BY POWER MODULE FAILURE.