SMD Help

Discussion in 'General Electronics Chat' started by snarf, Jun 26, 2008.

  1. snarf

    Thread Starter Active Member

    Jun 7, 2007
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    How does one find the value, voltage and type of unmarked SMD capacitors?

    Also on an SMD capacitor there is SQ1, does anyone know what it means?

    I have searched this forum and the Web but I'm still without answers.

    Does the colour and shape of the SMD capacitor relate to it's values and type? If it does where can I find related information.

    Thank you.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    You might be able to get up a rig to connect one to a capacitance meter, but voltage might have to be guessed at. Use the voltage in the existing circuit as a guide.

    There may be no way to tell a tantalum from an electrolytic cap. there should be polarity marks, though.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. aidafiza

    Member

    Jun 2, 2008
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    If you have an RLC meter,that would be a great way to approximate the value of your capacitors and resistors and also inductors in that case.
     
  5. snarf

    Thread Starter Active Member

    Jun 7, 2007
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    Thanks for reply.

    Yes that could be the only alternative but it’s as you said one can never tell a Tantalum from an Electrolytic.
     
  6. snarf

    Thread Starter Active Member

    Jun 7, 2007
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    Thanks for link and reply.

    I have been to that page before but I didn’t find my answers to “SQ1” and unmarked capacitors.
     
  7. snarf

    Thread Starter Active Member

    Jun 7, 2007
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    Thanks for reply.

    Most probably that will be my only option. Can it be done with the component still on board or will I have to unsolder the component and test it off board?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    OK, here's another page:
    http://my.execpc.com/~endlr/markings.html
    Scroll about halfway down.
    Usually, SMT/SMD ceramic caps have just one letter and a number. The case of the letter is significant.
    Now, from KEMET's site:
    http://www.kemet.com/kemet/web/homepage/kechome.nsf/weben/8C1829F0139DB7EECA2570A50016090A/$file/F3102_CeChPkg.pdf
    An excerpt of the document is attached.
    1st letter is the manufacturer code
    2nd letter indicates the value; "Q" indicates 3.9
    3rd character is the power of 10, in your case 10e1
    So, the cap is 39pF. Don't know who the manufacturer is offhand.

    As far as the unmarked capacitors, you'll need a capacitance meter to test them. Determining their breakdown voltage will likely turn into a destructive test. :eek: However, it's typical for 0603/0806 multilayer ceramic caps to have a rating of 50v.

    Attempting to determine the value of unmarked SMT caps while soldered on a board will be very frustrating, particularly if they're low value.
     
  9. snarf

    Thread Starter Active Member

    Jun 7, 2007
    56
    0


    Many thanks for the information looks like it is 39pF. The Kemet table states the marking is available only for Kemet chips, the capacitors don't have the K marking, only SQ1. Do you think this can make a difference? Should I double check with a capacitance meter?

    As for the unmarked I will be getting a capacitance meter soon and will try to unsolder them and determine the values.

    The only problem for unmarked smd capacitors is how to know if they are polarised or not. Any hints please.

    If an smd capacitor is in parallel with an electrolytic capacitor would that mean that the smd capacitor is most probably and electrolytic too?
     
  10. snarf

    Thread Starter Active Member

    Jun 7, 2007
    56
    0
    Sorry forgot to add.

    Can smd components such as capacitors, resistors, etc be replaced with non smd components or will this effect the circuit?

    Thanks
     
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