Maker Pro
Maker Pro

Faint, high-pitched noise

R

Robert Latest

Jan 1, 1970
0
Hello,

I just bought a used Wi-Fi router / ADSL modem combo. Everything works fine,
except that after the thing has warmed up for about 20 minutes, it emits a
faint, audible whine of a few kHz that's pretty annoying once you start
listening to it (as one does, and doesn't stop any more. I find myself
"searching" for that noise once I enter the room where the thing is).

I'm guessing that the noise comes from some switched POL regulator inside
the device. The wall-wart is one of the old, clunky, linear ones so that's
out. Question is what can be done about it, other than moving the bugger to
the attic. Something inside the case must be oscillating mechanically, and
the only thing I can think of that would do that is some inductor of the
switcher. My idea is to locate something that looks like a magnetic
component and soak it in liquid epoxy.

Good idea or bad idea?

robert
 
I

ian field

Jan 1, 1970
0
Robert Latest said:
Hello,

I just bought a used Wi-Fi router / ADSL modem combo. Everything works
fine,
except that after the thing has warmed up for about 20 minutes, it emits a
faint, audible whine of a few kHz that's pretty annoying once you start
listening to it (as one does, and doesn't stop any more. I find myself
"searching" for that noise once I enter the room where the thing is).

I'm guessing that the noise comes from some switched POL regulator inside
the device. The wall-wart is one of the old, clunky, linear ones so that's
out. Question is what can be done about it, other than moving the bugger
to
the attic. Something inside the case must be oscillating mechanically, and
the only thing I can think of that would do that is some inductor of the
switcher. My idea is to locate something that looks like a magnetic
component and soak it in liquid epoxy.

Good idea or bad idea?

robert

Just a thought before you pot it in epoxy and make any subsequent repair
impossible, see if any electrolytics are getting warm, it could be an ESR
problem - although this normally improves as the unit warms up, still its
worth a try.
 
G

Genome

Jan 1, 1970
0
ian field said:
Just a thought before you pot it in epoxy and make any subsequent repair
impossible, see if any electrolytics are getting warm, it could be an ESR
problem - although this normally improves as the unit warms up, still its
worth a try.

It could be the other way around...... I think you'll find that electrolytic
capacitor ESR goes down as they warm up. If it is a stability problem, which
is a good reason for things whining then that is a possibility.

Depending on how 'good' the manufacturer think they designed things it can
work the other way around. As electrolytics age their ESR goes up and that
might affect stability at the other end of things. Which sounds like a
possibility since it is second hand and presumably old. (!)

I assume you did not buy this from a freind or, if you did, they did not
hear it themselves.....

Since you are Robert Latest you probably have a scope so it would be worth a
prod to see what the supply voltage looks like....

DNA
 
I

ian field

Jan 1, 1970
0
It could be the other way around...... I think you'll find that
electrolytic capacitor ESR goes down as they warm up. If it is a stability
problem, which is a good reason for things whining then that is a
possibility.


You obviously have as much difficulty understanding English as you do with
washing yourself!
 
R

Robert Latest

Jan 1, 1970
0
ian said:
Just a thought before you pot it in epoxy

Well, I didn't really want to pot it, like into a whole block of plastic. I
have this lacquer-like stuff that I can brush or spray, so it would just
soak into the windings of the coil.

Thanks for the electrolytics/ESR tip.

robert
 
G

Genome

Jan 1, 1970
0
ian field said:
You obviously have as much difficulty understanding English as you do with
washing yourself!

You appear to have used reasonable English to provide a scenario whereby the
problem, as described, should in fact go away as the unit warms up. I'm just
pointing out that, technically speaking, your argument might be incorrect.

Then again, it's not uncommon for people with a good grasp of English to
have difficulty with technical issues. Logic appears to be a problem as
well. Still, one out of three isn't bad.

DNA
 
J

Jan Panteltje

Jan 1, 1970
0
On a sunny day (1 Mar 2007 14:53:41 GMT) it happened Robert Latest
<[email protected]>:

My idea is to locate something that looks like a magnetic
component and soak it in liquid epoxy.

Good idea or bad idea?

robert

I have use plastic spay in the past on noisy TV magnetics.
Worked sometimes, does little harm.
 
I

ian field

Jan 1, 1970
0
Genome said:
You appear to have used reasonable English to provide a scenario whereby
the problem, as described, should in fact go away as the unit warms up.
I'm just pointing out that, technically speaking, your argument might be
incorrect.

Capacitors with ESR problems typically improve slightly as they warm up,
although in my years of experience servicing TVs, monitors & SMPSUs I've
seen caps react in a way contrary to usual expectation in this regard, my
suggestion to the OP that the fault presenting once the unit had warmed up
shouldn't automatically preclude paying attention to the caps, like I said -
"still its worth a try".
 
I

ian field

Jan 1, 1970
0
Jan Panteltje said:
On a sunny day (1 Mar 2007 14:53:41 GMT) it happened Robert Latest
<[email protected]>:

My idea is to locate something that looks like a magnetic

I have use plastic spay in the past on noisy TV magnetics.
Worked sometimes, does little harm.

The Maplin PCB lacquer is even better - the can I bought never sets, it
stays gooey forever!
 
G

Genome

Jan 1, 1970
0
ian field said:
Capacitors with ESR problems typically improve slightly as they warm up,
although in my years of experience servicing TVs, monitors & SMPSUs I've
seen caps react in a way contrary to usual expectation in this regard, my
suggestion to the OP that the fault presenting once the unit had warmed up
shouldn't automatically preclude paying attention to the caps, like I
said - "still its worth a try".

Well, at least my shoes don't smell!

DNA
 
R

Robert Latest

Jan 1, 1970
0
Genome said:
I assume you did not buy this from a freind or, if you did, they did not
hear it themselves.....

I bought it from ebay at a very good price, and if I can't get rid of
the noise the thing will have to be move to a back corner. I'm just too lazy
to lay the wiring there.

robert
 
Top