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Impossible Circuit Board Repair?

Discussion in 'General Electronics Chat' started by Oakton, Sep 18, 2017.

  1. Oakton

    Oakton New Member

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    Many years ago I purchased a GE SuperRadio. It was considered an "expensive" radio, but I think it was the
    best portable AM/FM radio ever made. Because it has external connectors, you can pick up AM stations
    thousands of miles from your location with a decent antenna.

    For decades it functioned perfectly. A few days ago the volume control was damaged in a freak accident. I
    opened the case and was immediately impressed by the construction. All the components look brand new!

    There are three square pots soldered to the circuit board for treble, bass, and volume. Pot number four is a
    traditional round unit. It's fastened through a hole in the board with a control nut.

    There are seven guide wheels for the dial cord. The shaft for the round pot supports the two larger drive wheels.
    I have a spool of replacement dial cord, but that is not the problem. Pulling the board so I can unsolder the
    damaged volume pot will make this SuperRadio unusable.

    It's a classic "Catch-22," if you know what I mean. The drive wheels are buried under the board (solder side).
    Pulling the board will instantly remove the dial cord from the wheels. When the board is reinstalled you cannot
    run new dial cord, because the wheels are inaccessible.

    When this radio was assembled in the factory, several of the plastic structural components must have been
    glued or heat sealed after the dial cord was wrapped around the wheels. Obviously, reversing this process
    is impossible.

    I can think of a possible workaround, but it's not something I really want to try. If I can find an ultra tiny
    cut-off wheel for a Dremel tool, I could cut the volume control pins. Using conductive adhesive, I might be
    able to bond a replacement volume pot to the cut pins left on the board. The cut-off wheel would have to
    be extremely small so it doesn't damage nearby components. Maybe 1/8" maximum. Manufacturers of
    custom jewelery use tiny cut-off wheels. The cost for this type of precision bit is probably more than I
    want to spend.

    If you can think of a more rational solution, please let me know.
     
    Last edited: Sep 18, 2017
  2. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    The small, round burr (about 1/16") that comes with Dremel will do what you suggest. However, I have a hard time imagining a situation where you can get the burr there but cannot get a soldering iron to the same place.

    Maybe a picture would help.
     
  3. tomizett

    tomizett Active Member

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    It's hard to believe that a radio of such apparent quality would have been constructed in such a way that it could not be taken apart for repair - but I suppose it is possible.

    As John suggests, a picture would be great.

    <edit>
    As John again alluded to above, trying to glue a new pot in place would likely be a non-starter - it would have to be soldered. You may be able to un-solder the cut-off pins from the front side of the board.
     
  4. dave

    Dave New Member

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  5. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Let me add that you can solder a component on the copper side from the back side, even when there are not plated through holes.
    This bridge rectifier sits flush on the copper side. It is a one-sided board and was soldered from the side back side:
    upload_2017-9-18_17-54-31.png

    John
     
  6. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I've repaired radios professionally for many decades, and even cheap crap ones usually come apart for repair, and decently made ones are pretty well guaranteed to be designed to be repairable.

    I can't comment on GE (as they are presumably USA specific?), but it's most likely that you're 'missing something', and not disassembling it correctly.

    It's fairly common for the dial drive to stay as part of the cabinet, while the PCB is pulled away from it - and you have to make sure that the dial drive engages in the right place when you reassemble it.

    Have you tried google?

    http://www.davidmoisan.org/radio/superadio/gesr_app_A.html
     
  7. BobW

    BobW Active Member

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    Also quite a bit of info on this site:
    http://earmark.net/gesr/
    It covers the original Superadio, the Superadio II, and the Superadio III, including disassembly instructions and service manuals.
     
  8. Oakton

    Oakton New Member

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    Thanks for all your replies!

    I examined this radio with a very powerful headband lamp (1000 lumens) and dental inspection mirrors. For at
    least two hours I searched for hidden screws, clips, or any weird fastener that would allow access to those
    drive wheels after reinstalling the circuit board. I found nothing.

    There is a four diode bridge, capacitors, and a jumper wire very close to that damaged volume control. Heating
    those pins on the "wrong side" of the board will not accomplish much. The solder must be vacuumed up with a
    sucker or wicked away with a desoldering braid.

    Perhaps this radio should be given to a collector who has a lot of experience wrapping dial cord around those
    wheels. I would like to keep it, but I'm afraid anything I try might cause more damage.
     

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