No, it's not the fan, it's the oscillator I'm hearing, but I don't know
what components are doing the vibrating. The fan fires up occasionally,
but that noise is entirely different.

I've heard switching PSUs begin to hiss when the electrolytic filter
capacitors start to fail. These caps are in a stressful operating
environment - high ripple currents, and sometimes high temperatures.
They can dry out or leak (this is a particular problem with a whole
batch of Taiwanese-made caps which were manufactured with a defective
electrolyte formula), their ESR increases, and the circuit becomes
audibly noisy. I don't know whether the noise is direct microphonics
from the caps, or from the toroids.

Consider swapping out any suspect 'lytics in the supply with new ones,
preferably ones rated for switching-supply operation at 105 degree C.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

It was hissing right out of the box, it's brand new.
I don't suspect so much that it's defective, I hear a lot of switchers,
it's almost as if there's a couple of popular frequencies, and I happen
to be able to hear one of them. If I knew what section is resonating
(physically vibrating and transducing the sound that is) I could try to
drizzle a bit of super glue on it.

B.




Dave Platt wrote:


I've heard switching PSUs begin to hiss when the electrolytic filter
capacitors start to fail. These caps are in a stressful operating
environment - high ripple currents, and sometimes high temperatures.
They can dry out or leak (this is a particular problem with a whole
batch of Taiwanese-made caps which were manufactured with a defective
electrolyte formula), their ESR increases, and the circuit becomes
audibly noisy. I don't know whether the noise is direct microphonics
from the caps, or from the toroids.

Consider swapping out any suspect 'lytics in the supply with new ones,
preferably ones rated for switching-supply operation at 105 degree C.

On Mon, 07 Jun 2004 08:25:47 -0400, Bob wrote:

If I knew what section is resonating
(physically vibrating and transducing the sound that is) I could try to
drizzle a bit of super glue on it.

B.

You could always poke around inside with an insulated probe to shut
down the oscillating/vibrating component, and go from there.

Bob
k5qwg

"Bob Miller" wrote in message
...
On Mon, 07 Jun 2004 08:25:47 -0400, Bob wrote:

If I knew what section is resonating
(physically vibrating and transducing the sound that is) I could try to
drizzle a bit of super glue on it.

B.

You could always poke around inside with an insulated probe to shut
down the oscillating/vibrating component, and go from there.



Please note: Insulated probe does not mean a screwdriver with a plastic
handle (yes, I've known people that used them).

"Bob Miller" wrote in message
...
On Mon, 07 Jun 2004 08:25:47 -0400, Bob wrote:

If I knew what section is resonating
(physically vibrating and transducing the sound that is) I could try to
drizzle a bit of super glue on it.

B.

You could always poke around inside with an insulated probe to shut
down the oscillating/vibrating component, and go from there.



Please note: Insulated probe does not mean a screwdriver with a plastic
handle (yes, I've known people that used them).

On Mon, 07 Jun 2004 08:25:47 -0400, Bob wrote:

If I knew what section is resonating
(physically vibrating and transducing the sound that is) I could try to
drizzle a bit of super glue on it.

B.

You could always poke around inside with an insulated probe to shut
down the oscillating/vibrating component, and go from there.

Bob
k5qwg

It was hissing right out of the box, it's brand new.
I don't suspect so much that it's defective, I hear a lot of switchers,
it's almost as if there's a couple of popular frequencies, and I happen
to be able to hear one of them. If I knew what section is resonating
(physically vibrating and transducing the sound that is) I could try to
drizzle a bit of super glue on it.

B.




Dave Platt wrote:


I've heard switching PSUs begin to hiss when the electrolytic filter
capacitors start to fail. These caps are in a stressful operating
environment - high ripple currents, and sometimes high temperatures.
They can dry out or leak (this is a particular problem with a whole
batch of Taiwanese-made caps which were manufactured with a defective
electrolyte formula), their ESR increases, and the circuit becomes
audibly noisy. I don't know whether the noise is direct microphonics
from the caps, or from the toroids.

Consider swapping out any suspect 'lytics in the supply with new ones,
preferably ones rated for switching-supply operation at 105 degree C.