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mike chassis socket question

Discussion in 'Electronic Repair' started by RB, Feb 17, 2006.

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  1. RB

    RB Guest

    I have an older solid state scanning marine VHF radio I'm trying to get
    going again, after years of non-use.

    The mike is missing. These radios all used a simple PTT mike---a common
    ground, 12+ to one side of the PTT switch, and the audio from one side of
    the mike element on the other. Three wires total. I'd like to put a plug
    on a CB mike I have and use that for the marine VHF. I have no manual or
    schematic, and little chance of finding one (I'm searching).

    The chassis mike socket has 5 pins. I can easily find the ground pin. By
    powering the set up, I can then find the 12v+ pin. That takes care of two
    of my three wires in the mike cable.

    Question being, then, how do I determine which of my remaining 3 pins is for
    the audio lead?
     
  2. Arfa Daily

    Arfa Daily Guest

    This may sound like a silly suggestion, but why not just look at the back of
    the socket ? If there are actually still 3 unidentified wires going to it,
    you need to ask yourself what the other two are as well. If you really can't
    get to the back of the socket, you might be able to read something to ground
    on the mic-audio pin, using the high ohms range of an analogue multimeter.
    The chances are that the lead is capacitor coupled to the mic amplifier
    stage, but you still might just see a slight 'kick' from the needle.

    If you can't do either of these things, fire the radio up into a dummy load
    ( not an antenna please ) by pulling the 12v PTT line, then find the radio's
    output on a scanner, or another marine band radio. All that you then need to
    do, is touch each of the three unknown mic socket pins with the tip of a
    screwdriver, with your finger on the shaft, and listen on the monitor
    receiver, for the pin that produces a buzz. You've then found the mic-audio
    pin.

    Arfa
     
  3. RB

    RB Guest

    }}} If there are actually still 3 unidentified wires going to it,
    you need to ask yourself what the other two are as well. {{{

    Good point! I have to assume they were unused, as there were no other mike
    functions. I can get to the backside of the unit. But, if those pins are
    used, I won't know what they go to in the solid state mess.

    }}} All that you then need to
    do, is touch each of the three unknown mic socket pins with the tip of a
    screwdriver, with your finger on the shaft, and listen on the monitor
    receiver, for the pin that produces a buzz. You've then found the mic-audio
    pin. {{{

    Excellent idea!!! The feedback buzz should do the trick nicely.
     
  4. Perhaps a transmit switch?
     
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