Deaf Alarm Clock Rubber Button Issues

Discussion in 'Electronics Repair' started by PaulNM, Jan 10, 2017.

  1. PaulNM

    PaulNM

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    Hi all, I'm trying to fix up an old alarm clock that has a few bum buttons that don't really register anymore.

    I thought it would be a simple enough exercise, they're simple rubber buttons like you find on most remote controls. When I took it apart I discovered that while the buttons are just one sheet of rubber, none of them have any carbon disks or pills on the back. The circuit board they touch looks as expected, with circular areas of metal interlocking fingers that don't actually touch. I'm at a loss as to how this is even working at all, most of the buttons are still working fine.

    I did notice a good deal of a greasy substance all over everything. I did try cleaning it off a some buttons (one good, one bad), but it didn't seem to have any effect (good or bad).

    I'm mostly interested in understanding and learning more about how the buttons work, but would really appreciate getting the alarm buttons working more reliably. The alarm in question is a Sonic Alert SB1000, for deaf/hearing-impaired people. Those things are ridiculously expensive, so getting a few more years out of this would be nice.

    http://www.sonicalert.com/Combination-Alarm-Clock-p/sb1000.htm
     
    PaulNM, Jan 10, 2017
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  2. PaulNM

    KTW VIP Member

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    KTW, Jan 10, 2017
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  3. PaulNM

    PaulNM

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    I may be misunderstanding you, but can this stuff be directly used on the rubber/silicone buttons?

    Just to be clear, when I say there aren't any discs/pills, I'm not saying they fell off or broke. I mean there's no evidence there were any in the first place. (Nor is there debris of former discs/pills inside.) There's no sign that one could be mounted to the back of the buttons, they don't have flat areas or recesses. There is some webbing, but it doesn't line up properly. A number of the buttons still work fine despite the current situation.

    It sounds like you're suggesting using this paste to coat the backside of the buttons, let it dry and harden, then it'll act like a carbon disc. This makes sense to me, I'm just curious how well it'll stay adhered to the rubber/silicone.
     
    Last edited: Jan 10, 2017
    PaulNM, Jan 10, 2017
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  4. PaulNM

    KTW VIP Member

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    That's what it's designed to do, stick to rubber.
    There are different brands, do a search on it.
    You can do a continuity test with a meter to check the back of the rubber buttons.

    They may have used a conductive grease.
     
    Last edited: Jan 11, 2017
    KTW, Jan 11, 2017
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  5. PaulNM

    PaulNM

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    Thank you. I'm pretty handy and good at self-research, but the lack of a obvious contact mechanism really threw me for a loop. I first wrote clear instead of obvious, but then realized conductive grease is technically clear. :) Hadn't really heard of that before, but in hindsight it's obvious as I've seen graphite grease.

    The internals of this alarm clock are quite dated, it's pretty clear it was mostly assembled by hand. I'm not too surprised to hit an oddity like this.
     
    PaulNM, Jan 11, 2017
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  6. PaulNM

    shrtrnd VIP Member

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    KTW's advice is probably the correct solution.
    What you need to do, is make those contacts on the board connect.
    Any possibility of cutting and glueing little aluminum foil discs to the underside of the rubber button, so that when
    depressed, they make the circuit board traces connect?
    Just another thought.
    Like KTW said, there MUST have been SOME type of conductive material on the underside of those push-buttons
    that connected the trace on the board when the rubber push-button is depressed.
     
    shrtrnd, Jan 11, 2017
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  7. PaulNM

    tedstruk

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    I was told... don't quote me on this... That you can clean those carbon switches with a soft graphite pencil eraser. Personally, I try not to even touch them. The greasy stuff is probably contact grease, designed to help the buttons make contact. I think the contacts, are supposed to be lightly coated... but don't trust me... I am new to the momentary (intermittent) switch. They are fairly inexpensive to buy.
     
    tedstruk, Jan 11, 2017
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  8. PaulNM

    shrtrnd VIP Member

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    I can't think of too many more abrasive ways to try to clean a carbon contact button than with an eraser.
    I wouldn't try that.
    I use isopropyl alcohol only. But we don't even know if you HAVE carbon pads.
    If they're not just worn away, maybe KTW's idea of a conductive grease might do it?
     
    shrtrnd, Jan 11, 2017
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