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Curious buzzing sound on AM car radio

Discussion in 'Electronic Repair' started by Spooky, Oct 17, 2005.

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  1. Spooky

    Spooky Guest

    Hi All,

    I have a Motorola push-button AM car radio which is plagued with a
    buzzing sound on its audio. It is present at the low end of the medium
    wave band and it is right across the long wave band too. At first, I
    thought it was noise coming through the DC power adaptor I was using,
    but it was still there when I ran it in my car from a DC outlet. The
    buzz is only present with an antenna is connected and it almost
    disappears when you place a hand on the top of the radio chassis. I
    can't pick up this interference on any other radio and my ground
    connections to the chassis seem fine. I'm at a loss as to where to
    start fixing this! Any suggestions will be gratefully received.

    Regards,
    Gary
     
  2. Porky

    Porky Guest

    Your antenna lead may have a break in it or something loose at the
    antenna end. Check the routing of the cable under the dash.
     
  3. In the AM only days, it used to be the practice to use a thick braided
    earth strap from the radio chassis to a nearby body ground, even if it had
    a ground power wire. There was usually a captive 1/4" bolt on the back for
    this purpose. Think the theory was that RF needs a lower impedance ground
    than the power lead which may well be grounded someway off at a central
    point, and pick up interference.
     
  4. Mark

    Mark Guest

    is it really old i.e. does it have a vibrator type power supply? does
    it have tubes? or is it all solid state? how about if you drive your
    car to a field away from power lines and houses?


    Mark
     
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