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Capacitor Value

Discussion in 'Electronic Repair' started by bill, May 29, 2006.

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  1. bill

    bill Guest

    I'm repairing a couple of LCD monitors and determined the cause in
    both monitors to be defective Metalized Polyester film capacitors.
    They were damaged by excessive heat on the inverter board.

    The markings on the capacitor is "u18j100" ( the "u" looks like the
    "u" in "uf"). I found a similar capacitor in an old junk monitor
    board that has the marking "22j63". I put that in and the montiors
    work fine. I am assuming the numbers after the "j" (5% tolerance, I
    would think) indicate the working voltage, 100v vs 63v, so obviously I
    need to get the right part. However, I am uncertain as to the actual
    value of the original capacitor. Is this an 18 uf capactior, or 18pf,
    or something else. My guess would be 18pf, 100v. They are in plastic
    packages, about 7mm square, 3mm thick

    Thanks

    -Bill
     
  2. Pooh Bear

    Pooh Bear Guest

    It's an abbreviation of 0u18 or 0.18uF - J is the tolerance ( 5% ) and 100 is
    the voltage
    Very wrong. Surely you could see by the size ?
    Probably polyester film. Is it yellow plastic ?

    Graham
     
  3. bill

    bill Guest

    Well, I was pretty sure 18uf was out of the question, but I'm used to
    seeing two digits followed by a multiplier. I'm pretty sure they are
    METALIZED polyester film. They are in blue plastic. The ones I
    substituted from the junk monitors were in white plastic. I'm not
    sure the color means anything at all.

    0.18uf 100v Metalized Polyester film .... that should be it. Thanks!

    -Bill
     
  4. Pooh Bear

    Pooh Bear Guest

    Some manufacturers use the plastic colour as a code. Blue is often polypropylene.
    It's not a pulse capacitor is it ? It'll likely need to be polypropylene in that
    case.

    Graham
     
  5. Arfa Daily

    Arfa Daily Guest

    " u18 " is a fairly standard 'alternative' way of writing cap values. It
    makes sure that fly crap doesn't get accidentally read as a decimal point.
    Thus, a 2.2uF cap will often be seen written as 2u2 so it doesnt get
    confused for a 22uF. 4n7 is 4.7nF 6p8 is 6.8pF. You also find it done
    with resistors - 4k7 = 4.7k 3M3 = 3.3M 0R68 = 0.68 ohms and so
    on.

    The "100" after the j is 100v, so strictly speaking, the 63v types that you
    have substituted, are not sufficiently rated. Whether that's a problem, will
    depend on where exactly they are in the circuit, and what peak voltage they
    have across them. Manufacturers usually go for the 'cheap is best' option,
    so if 63's would have done in the first place, they probably wouldn't have
    fitted 100's.

    Arfa
     
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