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  1. #1
    Join Date
    Feb 2004
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    Oxley, Brisbane
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    Default Switch contact coating wearing out

    Hi

    I have a machine that uses a flexible rubber as the medium for contacting a pair of printed circuits on the circuit board itself. The rubber has a bump that has a coating of black conductive material on the contact surface area.

    Of late, this contact is getting harder and harder to make as the black conductive contact material seems to be wearing away from the rubber part. The circuit board is not worn at all and is still nice and shiny.

    The machine is about five years old and gets turned on/off at least 4 times a day, so it hasn't done too badly, but as I said before, it now takes several (up to 10 or 12) presses before the switch operates.

    Can anyone tell me what the black contact material is and if it is available in small quantities for repair jobs?
    Bob Willson
    The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.

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  3. #2
    Join Date
    Dec 2005
    Location
    Canberra
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    3,260

    Default

    It's a carbon filled conductive coating.

    Rubber Keypad Repair KIT | eBay

    A bit exxy for one contact though...you might have better (more cost effective) luck with some conductive paint from Jaycar.

  4. #3
    Join Date
    Jan 2007
    Location
    Katoomba NSW
    Posts
    4,770

    Default

    Depending on your soldering skills you could solder a couple of wires to the PCB and connect a standard pushbutton.
    I would also try spraying a bit of contact cleaner on the button contact surfaces.
    Those were the droids I was looking for.
    https://autoblastgates.com.au

  5. #4
    Join Date
    Mar 2009
    Location
    Brisbane
    Posts
    356

    Default

    I have used a small round or square of self adhesive aluminium foil tape over the rubber pad with some success.
    The 25 mm tape previously used for security monitoring of breaks in glass windows was good.
    Jaycar has a 25mm tape (cat NM2862).
    The problem will be with drift of the aluminium foil pad over time.
    If at all possible, install a C&K style push button switch.

  6. #5
    Join Date
    Jun 2005
    Location
    Townsville. Tropical Nth Qld.
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    1,243

    Default

    Bob, you could also find an old infrared aircon or tv control and swap a suitable button. A mate up here fixes them all the time by stealing carbon bits from old ones as most buttons are never used.
    Rgds,
    Crocy.

  7. #6
    Join Date
    Feb 2004
    Location
    Oxley, Brisbane
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    Default

    Thanks crocy
    A good thought but unfortunately the 'button' is a not actually a button. The shape of the contactor pad would not allow me to do this. Maybe I could harvest the carbon from the ends of old buttons and glue that to the pad instead.
    Bob Willson
    The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.

  8. #7
    Join Date
    Dec 2014
    Location
    Willunga, Australia
    Posts
    735

    Default

    I have used both the Jaycar silver paint and aluminium foil method. Both with limited success.

    I would advise that you opt for the ebay repair kit. Especially considering the use it gets.

    John

  9. #8
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    Feb 2004
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    Oxley, Brisbane
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    Default

    Thanks John
    I have ordered some from AliExpress
    Bob Willson
    The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.

  10. #9
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    Feb 2004
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    Oxley, Brisbane
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    Default

    The glue (which is what the contact repair kit stuff is called) came, I used it and it works perfectly.All contacts have been restored to normal. Thank you all.
    Last edited by Bob Willson; 5th June 2016 at 09:48 AM. Reason: Further explanation
    Bob Willson
    The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.

  11. #10
    Join Date
    Jun 2012
    Location
    Dungog
    Posts
    273

    Default

    Have you tried cleaning the rubber with some paper towel dipped in metho. I do this with reasonable success on remote controls.

  12. #11
    Join Date
    Feb 2004
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    Oxley, Brisbane
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    Default

    Hello dinosour

    Yes, I had previously used that method. It worked for a short while then it didn't.

    Using the carbon glue has made everything as good as new again
    Bob Willson
    The term 'grammar nazi' was invented to make people, who don't know their grammar, feel OK about being uneducated.

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