One last suggestion, then I'll call it a night...
Does the Mic cord seem to have any damage?
Un plug it, try a manual short test to see if the socket is ok...
With the radio on, Try Shorting the two bottom pins of the Mic socket the side that has the INDEX Notch, Pins 1 and 4 Together. Those two are the on the (usually bottom) portion of the socket that are by the Index Notch and Pin 1 is on one side lower, Pin 4 is the opposite side lower...across from each other on that Index Notch side...
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Why this? To see if the CB/PA switch or Mic Jack is goofy. You may have a bad wire in the Mic cord...OR Mic wire from the socket that is to Pin 4 may have a cold solder joint...
In PA, it would not matter if Pin 4 worked or not, you're using Pin 1 - Ground, Pin 2 - Audio, Pin 3 - when you're in TX Or PA mode - the Speaker is automatically grounded by the CB/PA Switch setting-THRU PA jack. It still uses 4 - but if it's not receiving - as you said, you can talk to yourself all day...
