faint hissing from power supply
 

I've got your joe-average ATX case and I can hear a faint hissing coming
from the power supply even after the computer is shut down. I can kill the
sound by flipping the switch on the back of the power supply (which kills
power into the psu). I know "faint hissing" isn't super descriptive, but
can anybody tell me whether I should be afraid of this psu? Is in the
process of frying itself? its capacitor? or some other part that I'd rather
not fry? Or is it no big deal and some psus make a bit of noise? I don't
have any past experience with this hardware, so I'm afraid I can't say if it
used to be quieter or not.

Thanks,
Ethan

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Looks like the electrolytic capacitors lost capacity (have bad esr), due to
cost we normally replace them when not ok.

If you have an esr-meter available you can measure then the caps in-circuit
and replace the bad ones. But a new power supply is probably cheaper then
the repair cost.

Greetings Peter

"hupjack" hupjack_nospamtoday_yahoo.com schreef in bericht
...
I've got your joe-average ATX case and I can hear a faint hissing coming
from the power supply even after the computer is shut down. I can kill
the sound by flipping the switch on the back of the power supply (which
kills power into the psu). I know "faint hissing" isn't super
descriptive, but can anybody tell me whether I should be afraid of this
psu? Is in the process of frying itself? its capacitor? or some other
part that I'd rather not fry? Or is it no big deal and some psus make a
bit of noise? I don't have any past experience with this hardware, so I'm
afraid I can't say if it used to be quieter or not.

Thanks,
Ethan

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my address.

This may be perfectly normal. Recall that the PSU outputs 5 volts even when
"off" so that the computer's wake-up functions can work. That means it's
still rectifying the incoming AC, chopping it at an ultrasonic frequency,
and running it through a transformer. I've always believed -- without a lot
of proof -- that ultrasonic transformer whine can sound like a hiss, because
the vibration has irregular components that are audible.

"hupjack" hupjack_nospamtoday_yahoo.com wrote in message
...
I've got your joe-average ATX case and I can hear a faint hissing coming
from the power supply even after the computer is shut down. I can kill
the sound by flipping the switch on the back of the power supply (which
kills power into the psu). I know "faint hissing" isn't super
descriptive, but can anybody tell me whether I should be afraid of this
psu? Is in the process of frying itself? its capacitor? or some other
part that I'd rather not fry? Or is it no big deal and some psus make a
bit of noise? I don't have any past experience with this hardware, so I'm
afraid I can't say if it used to be quieter or not.

Thanks,
Ethan

--

To e-mail me, replace "_nospamtoday_" with the "@" symbol when replying to
my address.

On 3-Jan-2005, "hupjack" hupjack_nospamtoday_yahoo.com wrote:

I've got your joe-average ATX case and I can hear a faint hissing coming
from the power supply even after the computer is shut down. I can kill
the
sound by flipping the switch on the back of the power supply (which kills
power into the psu). I know "faint hissing" isn't super descriptive, but
can anybody tell me whether I should be afraid of this psu? Is in the
process of frying itself? its capacitor? or some other part that I'd
rather
not fry? Or is it no big deal and some psus make a bit of noise? I don't

have any past experience with this hardware, so I'm afraid I can't say if
it
used to be quieter or not.

The PSU is on whenever the line power is on, it's waiting for
the PC's "on" button to be pressed. For this you need power.
Whether it should hiss or not is another matter, PSU's
have a high frequency switch mode inverter, and like TV's
with similar power supplies, they can make a high frequency
sound. Whether it's safe cannot be determined unless you can
determine which part is making the hiss, and it needs somebody
technically competent to run the PSU uncased and connected
to a PC.

"hupjack" wrote:
I've got your joe-average ATX case and I can hear a faint hissing
coming from the power supply even after the computer is shut
down. I can kill the sound by flipping the switch on the back of
the power supply (which kills power into the psu). I know "faint
hissing" isn't super descriptive, but can anybody tell me whether I
should be afraid of this psu? Is in the process of frying itself? its
capacitor? or some other part that I'd rather not fry? Or is it no
big deal and some psus make a bit of noise? I don't have any past
experience with this hardware, so I'm afraid I can't say if it
used to be quieter or not.

I think your power supply is dying. The high-pitched whine indicates
bad capacitors -- power supplies should be silent when the computer
is off but still plugged in. I would replace it before it fails, especially
if
it is more than 3 yrs old. Power supplies are cheap and easy to replace
so why take a chance. Bad voltages can create havoc on a PC resulting
in spurious reboots, corrupted data or damaged hardware (e.g. hard
drive).

Regards,
David

DMF wrote:
"hupjack" wrote:

I've got your joe-average ATX case and I can hear a faint hissing
coming from the power supply even after the computer is shut
down. I can kill the sound by flipping the switch on the back of
the power supply (which kills power into the psu). I know "faint
hissing" isn't super descriptive, but can anybody tell me whether I
should be afraid of this psu? Is in the process of frying itself? its
capacitor? or some other part that I'd rather not fry? Or is it no
big deal and some psus make a bit of noise? I don't have any past
experience with this hardware, so I'm afraid I can't say if it
used to be quieter or not.


I think your power supply is dying. The high-pitched whine indicates

To me, a whine and a hiss are entirely different things.

A whine I might be concerned about. I doubt a hiss portends more than
the usual evil associated with PCs.

bad capacitors -- power supplies should be silent when the computer
is off but still plugged in. I would replace it before it fails, especially
if
it is more than 3 yrs old. Power supplies are cheap and easy to replace
so why take a chance. Bad voltages can create havoc on a PC resulting
in spurious reboots, corrupted data or damaged hardware (e.g. hard
drive).

Regards,
David




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Hi!

While a whining noise might indicate trouble for your power supply, a soft
hiss is usually nothing to be concerned about. I've got a few things here
that make some degree of a soft hissing noise (two Microsoft wireless access
points and a multi-brand camcorder battery charger that hisses when charging
certain battery types) that have been doing so since new.

William

"hupjack" hupjack_nospamtoday_yahoo.com wrote:

I've got your joe-average ATX case and I can hear a faint hissing coming
from the power supply even after the computer is shut down. I can kill the
sound by flipping the switch on the back of the power supply (which kills
power into the psu). I know "faint hissing" isn't super descriptive, but
can anybody tell me whether I should be afraid of this psu? Is in the
process of frying itself? its capacitor? or some other part that I'd rather
not fry? Or is it no big deal and some psus make a bit of noise? I don't
have any past experience with this hardware, so I'm afraid I can't say if it
used to be quieter or not.

Switch mode power supplies can make noise. It just the magnetic components
(and sometimes capacitors) rattling. Hearing it depends on the switching
frequency which nowadays is most likely ultrasonic, however, a lightly
loaded switcher may have a much lower and possibly erratic frequency or
operate in audible bursts.

Modern supplies will offer a couple of amps at 5v for standby power, this
will be a switcher and will be on all the time mains is applied. When your
PC is off it will be lightly loaded so it is probably what you can hear.

If your PSU has a standby supply (check the label) and when 'off' it
doesn't smell or stay more than vaguely warm I would not worry about it.

I absolutely agree with the "safety first" standpoint of fix it before it
causes me havoc, and I didn't have much hope that my description of a "faint
hiss" would give ya'all THAT much to work with.

Definitely what I'm experiencing IS a hiss rather than a whine. Nothing
high pitched about it.. No squeak.. More like a faint rustling....
ssssssssssssssssssssssss

-Ethan

"hupjack" wrote...
I absolutely agree with the "safety first" standpoint of fix it before it
causes me havoc, and I didn't have much hope that my description
of a "faint hiss" would give ya'all THAT much to work with.

Definitely what I'm experiencing IS a hiss rather than a whine.
Nothing high pitched about it.. No squeak.. More like a faint
rustling.... ssssssssssssssssssssssss

You've got me stumped. I've never heard a peep out of a power
supply when the PC was off except when they are failing due to
bad caps. Perhaps you can email the manufacturer and see if the
noise is normal. Also, how old are your ears? I know that we
lose the ability to hear high pitch as we age, so maybe it is a high
pitch but all you hear is rustling... just a thought. I've serviced PCs
that had power supplies that were squealling so loud you could
hear it across the room -- but the client (around 70 y.o.) didn't
hear a thing even when he put his ear right next to the computer.

BTW, how old is this power supply?

Good luck!

Regards,
David

As an electronics engineer who works on many types of rather expensive
switch mode power supply (but not PC ones) I believe I can answer your
question. Yes, it could be dried out caps gone low in capacitance or high
in ESR causing an instability, but it can also be a function of the supply
being too efficient for it's own good. When a switched mode supply is asked
to deliver very low output power (i.e. standby) then it has to reduce the
switching waveform width to a very narrow pulse so as to achieve a low
average power output. The pulse width modulator (PWM) IC will only work
reliably down to a certain width pulse which may still be too wide to
achieve the low power required. The result is that the feedback that is
there to maintain a constant output voltage controls the PWM IC by
'chopping' the switching pulses, so you may get a string of pulses followed
by a period of no pulses, then another string of pulses, another gap etc
etc. This isn't too precise, so the number of pulses and gap times varies a
bit; the overall choppiness usually occurs at audio frequencies and can
sound very much like a hissing noise being radiated by the output inductors
or transformers.

A resistor across the standby 5v to waste a bit of power would cure this if
it's the cause, possibly something like 47 - 100 ohms 1 watt but I'm
guessing. A lot of switch mode supplies have a minimum load rating so doing
this is normal practice with a lot of designs anyway. If it doesn't fix it
then I would say change the supply as it's probably a cap failing.



"hupjack" hupjack_nospamtoday_yahoo.com wrote in message
...
I absolutely agree with the "safety first" standpoint of fix it before it
causes me havoc, and I didn't have much hope that my description of a
"faint hiss" would give ya'all THAT much to work with.

Definitely what I'm experiencing IS a hiss rather than a whine. Nothing
high pitched about it.. No squeak.. More like a faint rustling....
ssssssssssssssssssssssss

-Ethan

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news.individual.net]

[Followup-To set to s.e.components]

mc stated:
This may be perfectly normal. Recall that the PSU outputs 5 volts even when
"off" so that the computer's wake-up functions can work. That means it's
still rectifying the incoming AC, chopping it at an ultrasonic frequency,
and running it through a transformer. I've always believed -- without a lot
of proof -- that ultrasonic transformer whine can sound like a hiss, because
the vibration has irregular components that are audible.

AFAIK, the hissing sound when on is from the magnetics of the SMPS or
other transformers - they operate at high frequencies.

But when off? Maybe by "off" you mean "stand-by" mode?

My PC uses an AT power supply so the power switch is "hard" - it kills
power to the PSU.

And anyway, I switch everything off using the 'line filter'.


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