MikeMl writes:

Short from microphone connector ground to chassis.

Bingo,

Proper installation of aircraft mic and headphone jacks requires the
use of insulating bushing where the threaded sleeve on the jack would
otherwise come in electrical contact with the airframe.

And those those who've not seen them, you need shoulder washers.



...[======| |======]
PANEL| |****PANEL
.......[==| |==]
...[======| |======]



The outer [here lower] washer is two-step; the inner part centers the
jack in the panel hole. Sometimes the inner [here upper] washer is flat,
sometimes it's the same as the lower. Both are usually made of phenolic
or such; but could be any insulator.

And note that if any mike jack wiggles loose/gets off-center, you can get
a short. It's an easy thing to inspect.

And if the jack is mounted on a plastic panel; you can skip the whole
issue. I don't know how many are.


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