This might sound strange but does your vhf
have a "hail" or "loudhailer" function. I had a King vhf
that had this function and once in a while I'd press that function button by mistake and, not having any loudspeaker hitched up, nothing would happen when I talked. The first time it happened I even went up the mast to check the antenna. A friend had the same unit and thought I was a genius when I fixed his "non-transmitting" vhf
. Of course he'd pressed the hail button inadvertently. Anther thing to look for is an "intercom" function. That might be on.