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discharging capacitor?

Discussion in 'Electronic Repair' started by /v\\onster /v\\asher, Nov 12, 2003.

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  1. I'm having problems figuring out what is causing this sound in my audio
    mixer. The only other components are resistors and transistors, so am I
    right to assume capacitor?
    Here is an MP3 of the unit being turned on and off.

  2. What brand and model mixer is it?

    Jeff Stielau
    Shoreline Electronics Repair
    344 East Main Street
    Clinton,CT 06413
    860-664-3535 (fax)

    "If you push something hard enough it will fall over."
    Fudd's First Law of Opposition - Sir Sidney Fudd
  3. Tweetldee

    Tweetldee Guest

    Nope.. you can't assume anything here. Your audio clip sounds like an
    oscillation, which could be caused by a number of things. What
    troubleshooting have you done? What kind of test equipment do you have?
    What troubleshooting skills do you have? Do you have a schematic of the
    unit? Is it a mono or stereo mixer? Does it have an equalizer? Mike
    input? Answers to those questions will help get off on the right foot,
    without a lot of back & forth, and wrong assumptions.

    Have you unplugged all the inputs to the mixer? If not, unplug ALL inputs
    and see if the problem goes away. If not, then your problem is definitely
    in the mixer. If it does, then troubleshoot the device that caused the

    The very first thing you should check is the power supply. Make sure that
    the output voltages are correct, and they are clean; that is, no ripple or
    noise on the lines. If the power supply voltages seem good, you should
    check the ripple and noise with a scope, if you have one. If you don't have
    one, check with all your friends & neighbors that dabble in electronics...
    you might luck out. If you have a digital multimeter with a sensitive AC
    function, use it in leiu of a scope. The DMM should read nearly zero of the
    lowest AC voltage scale. Power supply capacitors are suspect if there is
    any ripple or noise present.

    Next thing is to determine if the noise is on both channels, if this is a
    stereo mixer. If it is a stereo unit, and the noise is on both channels,
    then the power supply becomes your primary suspect. If it's a stereo unit,
    and the noise is on only one channel, then you have a good channel to use as
    a standard, which you can use to troubleshoot the bad channel.

    Tweetldee at att dot net (Just subsitute the appropriate characters in the

    Never take a laxative and a sleeping pill at the same time!!
  4. Since it's analog and I don't know much, I've just touched the negative
    leads on the capacitors.
    I've found two spots which hum like crazy when touched, and I've replaced
    it's capacitors.
    Only a DMM
    No schematic, it's stereo, no EQ, 2 mic inputs.
    yes they've all been unplugged.

    There is nothing as far as I can tell using a DMM's AC mode.
    It is a stereo mixer and the noise is on both channels.
    thank you.
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