What was found
DURING FLIGHT CREW PREFLIGHT, CREW FOUND WHEN OXYGEN MASK MICROPHONES WERE TESTED THE FLIGHT INTERPHONE STARTED TO EMIT A VERY LOUD SQUEAL. TO FURTHER TROUBLESHOT, DISCONNECTED ALL MICROPHONE INPUTS INTO THE FLIGHT INTERPHONE SYSTEM. WITH SAME RESULTS. CONITINUED TROUBLESHOOTING IAW WDM 23-51-11 AND FOUND FLT INTERPHONE JACK INTERNALLY SHORTED AT PINS 6 AND 7 ON CONNECTOR D5938. REMOVED AND REPLACED THE ELECTRICAL JACK IAW SWPM AND OPS CHECKED NORMAL IN ALL INTERPHONE MODES.