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HELP! Capacitor identification needed

Discussion in 'Electronic Basics' started by Eric R Snow, Oct 10, 2005.

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  1. Eric R Snow

    Eric R Snow Guest

    Thanks for looking at my post. I am clumsy and broke a capacitor off a
    circuit board in an encoder. This encoder is probably 30 years old.
    The capacitor is made, I think, by NEC, because it has marked +NEC at
    the bottom. The device has the following markings: 6.8-M


    The letter "E" after the "20V" is twice as big as all the other
    letters and numbers. I have contacted NEC and they said they cannot
    help me, the device is too old. I think it might be a tantalum
    capacitor. The reason I think it's a capacitor is because the circuit
    board has printed on it "C1" and the symbol of two parallel, vertical
    lines with each line having a line perpendicular and bisecting the
    vertical line. These markings are right next to where the capacitor is
    soldered to the circuit board. This capacitor is soldered across the
    positive and negative where the 5 volt power comes in to the encoder.
    Thanks for any help.
    Eric R Snow,
    E T Precision Machine
  2. Bob Eldred

    Bob Eldred Guest

    This could be a 6.8 Microfarad 20 Volt tantalum cap if it is across a power
    supply connection as you have indicated. Fortunately this is a non-critical
    application and it may not even need a cap there depending on how much
    by-passing is done elsewhere in the circuit, assuming your description is
    correct. The purpose of the cap is probably to reduce noise on the 5 Volt
    line and has little to do with the operation of the encoder, per-se. Remove
    the cap and see if the circuit works without it. A new 6.8 uF 10V or more
    aluminum or tant electrolytic cap should work fine in that application if
    you feel it needs replacing or if there is any noise or erratic behavior
    without a cap. Be sure to observe the polarity of the cap when replacing it.
  3. Eric R Snow

    Eric R Snow Guest

    Thank You Bob,
    It seemed to me that the cap was there for some kind of filtering. I'm
    glad that my guess was probably correct. I'll try the thing without
    the cap to see what happens but I'm going to buy and install a new cap
    anyway. This encoder is used in a machine shop with other cnc machines
    nearby and a TIG welder in the same building. I don't know much about
    how noise is picked by wires but I can hear the servo amps on one
    machine through an AM radio.
  4. Rich Grise

    Rich Grise Guest

    Then replace the cap before you try to run it - it helps filter out
    that noise so that your encoder will operate reliably.

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