Checking failed capacitor

Discussion in 'General Electronics Chat' started by kamiokande, Mar 21, 2010.

  1. kamiokande

    Thread Starter New Member

    Mar 21, 2010
    2
    0
    Hi, I've been having problems with an electric shower recently and have taken it to bits to try and find the problem. On the main circuit board there's a blue capacitor that has some green colouration to the top of it (I've attached a picture below). I wonder if someone could tell me if this is a likely sign that the capacitor has failed? There is an identical capacitor on the same board that does not have this colouration.

    If it is likely that the capacitor has failed could anyone help me identify a replacement. The capacitor has this written on it:

    WKO
    440 - X1
    250 - Y2
    1n M

    I'm not sure what this means as I'd expect to see a F to indicate a size in farads.

    If anyone could offer any help it would be much appreciated.

    Thanks.
     
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  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It's a Vishay WKO capacitor for AC.
    Datasheet for a similar better-than part: http://www.vishay.com/docs/22204/wko.pdf
    It's a 1nF cap, or 1,000pF

    I think the green glob is just some adhesive that got dripped on the cap during manufacturing. If it were cracked or burned, then I'd say it needs replacing.
     
  3. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    being in the environ of a shower, I would wonder if humidity did the deed.
    The cap in question, looks as tho it got hot enuf to boil its epoxy dip before it failed. That would assume that it sits top-up - heat rises........

    Sarge........is it advisable to replace a tantalum cap in such a circuit with an electrolytic ?? otherwise pls. forgive he inexperienced guesswork.
     
  4. kamiokande

    Thread Starter New Member

    Mar 21, 2010
    2
    0
    Hi, thanks very much for the replies. Thanks for the datasheet, I've found somewhere that I can order that part from.

    The capacitor would be horizontal during operation, so would any bulge/discolouration more than likely appear on the back of the capacitor (i.e. the upper most side)?

    Is there any way of testing the capacitor? I only have access to a digital multimeter and some simple electronics at the moment. I've tried searching and found this thread. But I get nothing on my multimeter following VincinChristmas' method, perhaps this cap is too small or my multimeter is just rubbish.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    I have never seen a cap like that fail by emitting translucent green goop. I'm not saying it's impossible, just unlikely - as they don't have green goop inside them.

    Usually you would want to replace a cap with the same type of cap, with the same capacitance rating, and the same or higher voltage rating. That isn't a tantalum cap, BTW.
     
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    1nF is too small to be measured by a typical DMM, even if it has a capacitance test function. Most DMM's won't measure less than 2nF. They simply have too much stray capacitance and inductance in the test leads to be accurate enough for smaller values of capacitance.

    You'd either need a dedicated capacitance tester, or you could build a 555 astable circuit and measure the output frequency.
    If you used 4.7k for R1, 1MEG for R2, and your 1nF cap for C1 in the standard astable configuration, you should see about 720Hz out from the 555 timer.
     
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