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Garrett Groundhog Help needed

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  • Garrett Groundhog Help needed

    Not sure where to look to solve this problem.
    A Groundhog I bought is working but the threshold increases when you touch the handle.
    Couldn't see any grounding problems, I am sure it's there somewhere.

    I did try disconnecting the retune toggle switch on the handle from the PCB. Threshold still rises when handle is touched.

    Any chance it might be coil connector related?
    Any help is appreciated.

  • #2
    did you already try to replace the aged electrolytics caps?
    Occasionally I noticed that problem on some older detectors, mostly IB or early VLFs.
    Although it was not initially intended, on some detectors the problem vanished after I replaced the (presumably) dried out electrolytic caps.
    Hoping this helps

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    • #3
      Yes I actually did replace them, the problem was there before that.
      To clarify the threshold rises about 5 bars on the meter from where you set the threshold.

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      • #4
        Sven, the problem was discussed in 2009 on the thunting forum:
        http://www.thunting.com/smf/modifica...43215#msg43215
        If you can't see the schematic, I will post it.

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        • #5
          Originally posted by mikebg View Post
          Sven, the problem was discussed in 2009 on the thunting forum:
          http://www.thunting.com/smf/modifica...43215#msg43215
          If you can't see the schematic, I will post it.
          Saw that posting but, nothing about the problem I am having. I will see what happens when I move the wires about. Ordered new coil connectors and control box connectors anyways, so I can switch over to 4 pin instead of the 5 pin used on my unit. The 5 pin connector uses only 4 pins just like all the older Groundhog units.

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          • #6
            When you look at the PCB inside you will see a small piggy back board with a metal can Op Amp on it.

            That is the sample and hold used to keep the threshold tone steady.

            Change the Caps on that mini board.

            This one is on a S-4 but yours will look the same.
            Attached Files

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            • #7
              Thanks, funny thing was I was going to replace those caps when I replaced the others. Since I would have had to order them, not the easiest to find that value, so did not replace them.
              Will go out and get some and replace them, since the snow and ice won't be gone for another couple months.....

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              • #8
                They don't need to be exactly the same.

                200VDC is way over kill. There just using them to keep the leakage down.

                Low Leakage same values of uF.

                This is good!

                http://www.mouser.com/ProductDetail/...DIsTkYAQryw%3d

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                • #9
                  Originally posted by homefire View Post
                  They don't need to be exactly the same.

                  200VDC is way over kill. There just using them to keep the leakage down.

                  Low Leakage same values of uF.

                  This is good!

                  http://www.mouser.com/ProductDetail/...DIsTkYAQryw%3d
                  I did replace those two Midwec caps, didn't solve the problem.
                  I also replaced the coil connectors on the box and searchcoil. Used better wire and rewired the coil connector on the box to the PCB.

                  In manual operation (toggle switch on box)
                  Still getting slight threshold increase in VLF mode and a slight decrease in Disc mode. Threshold just a tad too high to hunt comfortably with and a bit too low in disc so there's depth loss. If I switch the box toggle to auto operation, threshold remains steady and totally huntable in either mode.

                  The good thing so far is that there is just about no increase in threshold when you touch the handle.

                  I don't want to give up on this unit yet. Remarkable air test depth for an older unit.
                  Faint repeatable signal at 23cm from a small 10cm dia. silver half dime, about 33cm from a large man's 14kt wedding ring, in disc. mode.
                  Attached Files

                  Comment


                  • #10
                    I have read elsewhere that someone started replacing the resistors and the other poly caps.

                    Since I haven't had any replies, with some time on my hands will start replacing the poly caps, then see what happens.

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