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Thread: Can anyone identify a capacitor for me

  1. #1

    Default Can anyone identify a capacitor for me

    image1_jpeg.jpg
    I have a serial/parallel ISA card for my IBM XT 286 which doesn't seem to work.
    I think the issue maybe these capacitors because the computer doesn't power on when the card is installed.
    If I can remove and replace these capacitors I might be able to get the card working again.
    Thanks.

  2. #2
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    Looks to be a 10 uF, 16V tantalum, probably Kemet. Note that the outer legs are connected, so the center leg is + and the outer legs are -. This particular arrangement allowed for PCB stuffing without having to be aware of the polarity of the tants (a reversed cap can explode).

  3. #3

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    +1
    It's 10uF 16V tantalum with the three-legged - + - trick (I haven't seen them on non-IBM boards so far). You can check with a multimeter if there's any supply rail shorted on your ISA board anyway.

    Frank

  4. #4

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    I'm not sure it is a capacitor. It may be a resonator. In any case, if it were a capacitor, it would likely be a ceramic disk. In all my years of working on many electronics items. I've never seen a ceramic disk fail. The only ceramic capacitor I ever saw fail short was a glass encapsulated capacitor ( not likely seen on consumer electronics ).
    It might be a tantalum capacitor as a filter. They do fail. You can try to carefully remove it and see if it works, without it. Most of these are overkill and the system can run without one or two of them. It is also possible that it is a MOV. These are protective devices and can fail as well.
    Anyway, I don't recommend willy-nilly replacing capacitors unless you know the part has failed. You can carefully remove the part and check it for shorts with an Ohm meter. I can't see what it is connected to but I suspect it is power rails. If this is true, besides not working, it would likely cause the entire system to not turn on if it were loading the power rails.
    Like I say, try removing it to see if it works without it.

    I see Frank recognizes it as a tantalum. Like I say, try removing it. If bad, things should work without it.
    Dwight

  5. #5
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    No, it's a tantalum; a Kemet UltraDIP II, more precisely:

    Datasheet here

    They're still sold.

    There's a bit on MZD on this one: http://www.minuszerodegrees.net/fail...%20-%203lt.htm

  6. #6
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    The photo is of C11 on an 'IBM Serial/Parallel Adapter' (shown at [here]). The circuit diagram indicates its value to be 10F, and that it sits on the +12V line.

    C12 is also 10uF, and it sits on the -12V line.

    C21 is also 10uF, and it sits on the +5V line.

    Based on what is shown at [here], the 10F 16V tantalums that fail in the IBM 51xx family, are predominantly on the 12V lines. And so I am placing my bet on C11 or C12.

  7. #7

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    Thanks for your help, I've found these on eBay https://www.ebay.co.uk/itm/5-x-10uF-...4383.l4275.c10 Hopefully they'll do the trick.

  8. #8
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    You might want to find cap's with a higher voltage rating. See derating tantalum capacitors: https://www.avx.com/docs/techinfo/Vo...Capacitors.pdf
    Crazy old guy with a basement full of Pentium 1 laptops and parts

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