discharging capacitor?

[/v\\onster /v\\asher]

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.
http://tinyurl.com/unz0

Thanks

 

[Shoreline Electronics]

What brand and model mixer is it?


--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)
jstielau@snet.net
========================
"If you push something hard enough it will fall over."
Fudd's First Law of Opposition - Sir Sidney Fudd


"/v\onster /v\asher" <no-one@no-where.no> wrote in message
news:XdGdnWqGS8dWeCyiRVn-gg@comcast.com...

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.
http://tinyurl.com/unz0

Thanks

 

[Tweetldee]

"/v\onster /v\asher" <no-one@no-where.no> wrote in message
news:XdGdnWqGS8dWeCyiRVn-gg@comcast.com...
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.
http://tinyurl.com/unz0

Thanks

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
noise.

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

Never take a laxative and a sleeping pill at the same time!!

 

[/v\\onster /v\\asher]

"Tweetldee" <dgmason99@att99.net> wrote in message
news:2JVsb.251922$0v4.17271975@bgtnsc04-news.ops.worldnet.att.net...

"/v\onster /v\asher" <no-one@no-where.no> wrote in message
news:XdGdnWqGS8dWeCyiRVn-gg@comcast.com...
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.
http://tinyurl.com/unz0

Thanks

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?

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.

What kind of test equipment do you have?

Only a DMM

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.

No schematic, it's stereo, no EQ, 2 mic inputs.

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
noise.

yes they've all been unplugged.

[snip]

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.

There is nothing as far as I can tell using a DMM's AC mode.

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,

It is a stereo mixer and the noise is on both channels.

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

Never take a laxative and a sleeping pill at the same time!!

thank you.

 

[/v\\onster /v\\asher]

"/v\onster /v\asher" <no-one@no-where.no> wrote in message news:...

I've found two spots which hum like crazy when touched, and I've replaced
it's capacitors.

sorry about responding to my own post, but Iforgot to state that the problem
was not fixed after the capacitors were replaced. These capacitors are on
the 2 input channels.

 

[The Al Bundy]

"/v\onster /v\asher" <no-one@no-where.no> wrote
news:n7ydnaillP3wwymi4p2dnA@comcast.com...

"/v\onster /v\asher" <no-one@no-where.no> wrote in message news:...

I've found two spots which hum like crazy when touched, and I've
replaced
it's capacitors.


sorry about responding to my own post, but Iforgot to state that the
problem
was not fixed after the capacitors were replaced. These capacitors are on
the 2 input channels.

By touching the inputs you inject a 50/60Hz noisy sinewave. This causes it
to hum very hard. Every sensitive amp does it

Your mp3 file sounds like something is oscillating. This is normally caused
by bad capacitors (the electrolyte ones) and maybe some bad transistors. It
can also be that some volume knob (or any knob) makes a bad contact.

Good luck with it!

Al