What was found
ON APPROACH, A LOAD SIDE TONE WAS HEARD IN THE HEADSETS. PILOTS WERE UNABLE TO ESTABLISH COMMUNICATION WITH ATC DUE FOR FEEDBACK HUM NOISE GENERATED IN AUDIO SYSTEM, AND ALSO EMERG SELECTION IN AUDIO CONTROL PANEL WAS INOP. TROUBLESHOOTING FOUND THE AUDIO REMOTE ELECTRONIC UNIT (REU) CIRCUIT CARD NR 1 (P/N 5190-60-1) CONNECTORS CONTACT TO MAIN MOTHERBOARD WAS HEAVY CORRODED DUE THE PROTECTIVE COATING AT CIRCUIT BOARD WAS NOT APPLIED AS PER MIL 1-46058 AS STATED IN COMPONENT MM, THUS SHORTING OUT ALL SIGNALS AND INDUCING FEED BACK NOISES. THIS REPAIRED UNIT WAS RECEIVED FROM THE FAA REPAIR STATION AVTECH CORPORATION NR IG6R621N ON DECEMBER 2003 AND INSTALLED ON THE AIRCRAFT WITHIN THE SAME MONTH.