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Capacitor polarity

  1. Feb 10, 2009 #1

    DaveC426913

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    I'm an only somewhat-experienced electronics tinkerer. I'm working on a board from an older widescreen TV. It has these kinds of capacitors:
    _NVCAP.JPG

    I've looked everywhere online.

    Which edge is negative? The black(purple) or the grey?
     
  2. jcsd
  3. Feb 11, 2009 #2
    There is another way to determine which side is the + side and the - side. The + side's lead will be longer than the - side's lead.
     
  4. Feb 11, 2009 #3

    MATLABdude

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    Considering that these are surface mount capacitors, I believe it will be quite difficult to determine which lead is longer. However, there is a standard for this (assuming these are compliant parts). The side with the stripe on top indicates the negative lead, and the side with the bevels indicates the positive one:

    http://www.marketa.com/cht/pdf/ele/sc_series.pdf [Broken]
     
    Last edited by a moderator: May 4, 2017
  5. Feb 11, 2009 #4
    If all else fails, measure the resistance across the leads. Then reverse the polarity and measure the resistance again. The polarity that gives the highest resistance is correct.
     
  6. Feb 11, 2009 #5

    DaveC426913

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    Not if I'm examining an existing board!

    How does that tell me which is the negative lead?

    See, I'm replacing all these capacitors with newer ones of a different type. I don't know the circuit. I know what's negative on my existing caps, I just need to know which way to put them in.

    Looks like the negative side of a cap is always indicatged by the "stripe" or "bar".

    Good. That means I put them all in correctly and don't have to redo the whole thing!:tongue:
     
  7. Feb 11, 2009 #6
    Can you power up the circuit and measure which is negative on the caps? If not, usually circuits have a positive supply and a negative ground. Many times large caps have the negative side connected to ground.
     
  8. Feb 11, 2009 #7

    DaveC426913

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    Alas, all my careful soldering seems to have been for naught. Now the TV gets no picture.

    Most likely I've fried the board with my ham-fisted soldering iron technique.
    Second most likely, I've broken some of the delicate traces when the capacitors came off.

    Oh well, it cost me nothing.
     
  9. Feb 11, 2009 #8

    dlgoff

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    Use some 30ga wire to bridge the broken traces. Don't give up yet.
     
  10. Feb 11, 2009 #9

    DaveC426913

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    Yeah but the trouble is, they're so fine and they're multi-layered on the PCB so it's virtually impossible to tell where they connect to.
     
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