Problem: there is a high pitch whine that varies with engine RPM.
Reason: the microphone jacks may not have been insulated from the aircraft frame when the intercom
was installed.
Solution: insulate all microphone jacks from the aircraft frame.
Reason: a separate ground wire may not have been installed from each microphone jack to pin 13 on
the intercom.
Solution install a separate ground wire to pin 13 from each microphone jack.
Reason: the ground lead from pin 1 on the intercom may not be connected to the avionics ground.
Solution: attach the ground lead from pin 1 on the intercom to the avionics ground.
Reason: if the noise is very loud, a commercial alternator noise filter may need to be installed in series with the
intercom power lead.
Solution: install a commercial alternator noise filter in series with the intercom power lead.
Reason: a diode in the alternator may be defective.
Solution: replace the diode.
Reason: the aircraft battery may need to be replaced.
Solution: replace the aircraft battery.
Problem: a high pitch whine or squeal is always present.
Reason: if the noise is coming from the turn and bank indicator or other electric gyro, the system may be
incorrectly connected to the flight instrument power breakers.
Solution: connect the intercom power to the avionics power bus.
Reason: if the noise is coming from the turn and bank indicator or other electric gyro, the intercom may not be
insulated from the airframe.
Solution: do the following:
1. Insulate all microphone jacks from the aircraft frame, and run a separate ground wire from each
jack to pin 13 on the intercom.
2. Be sure the ground lead from the intercom is connected to an avionics ground wire.
Reason: if using a monaural headset, the switch next to the headphone jack may be in the Stereo setting.
Solution: switch to the Mono setting.
Reason: if using a stereo-capable headset, the Mono/Stereo switch on the headset may be in the Mono setting.
Solution: switch to the Stereo setting.
Problem: the intercom is not loud enough, or you lose parts of your sentences.
Reason: you may not have placed the microphone close enough to your lips.
Solution: place the microphone 1/8 inch from your lips to the side of your mouth.
Reason: the squelch may be adjusted too high.
Solution: while no one is talking, slowly rotate the Squelch control knob counterclockwise until you hear back-
ground noise, and then rotate the knob clockwise until the noise just disappears.
Reason: your headset may not be putting out a strong enough signal.
Solution: adjust the microphone pre-amp located on the headset microphone or in the earcup to equalize the
sensitivity of your headset.
Problem: you are unable to squelch out all background noise.
Reason: if you are using a David Clark H10-30 headset, the microphone pre-amp may not be turned down.
Solution: rotate the small nylon screw at the front of the microphone completely counterclockwise to decrease
the microphone pre-amp output.
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