q_q_anonymous@yahoo.co.uk wrote
> Rod Speed wrote
>> q_q_anonymous@yahoo.co.uk wrote
>>> Sergio T.P. wrote

>>>> I've bought a new 400 W power suply. It was supposed to be
>>>> a silence power suply. In fact, it is less noisy than my old one,
>>>> but when I turn on the compueter it makes a lot of noise...
>>>> It's not a regular noise, like the noise of a fan. It's some kind
>>>> of tickling sound... In 3 / 4 minutes it goes lower untill it gets
>>>> the normal level of noise of the power supply. Sometimes the noise
>>>> disappears when I lift a bit the case and let it down again, or if
>>>> I shake a bit the case... Extrange thing is that I had exactly the
>>>> same problem with my OLD power supply... (high sound when
>>>> switching on).

>>>> It that normal?? perhaps it sounds untill it warm up or something??

>>> you have to narrow this down. It's important that you
>>> sort of found a trigger. THe defeault position causes
>>> the noise. But lifting the case a bit stops the noise.

>> Thats an absolutely classic example of case vibration, that lifting effect.

>> Presumably the case warms up enough to expand
>> whats a bit loose enough so it doesnt vibrate anymore.

>> It might also be a resonance effect with one of the variable speed
>> fans running a little faster once its warmed up so you dont see the
>> a resonance effect with the case once its warmed up a bit.

>>> try taking the power supply out of the case. If it makes a noise
>>> then, it's easy to narrow down. If it doesn't make a noise, great.
>>> Put it in the case, turn it on, see if there is a noise. If so,
>>> take it out, or move it somehow, put it in a bit differently.

>> Its unlikely to be the power supply given that he
>> gets that effect with two different power supplys.

> yeah, but since this method involves taking the PSU out of the
> case anyhow, and running the PSU out of the case, it's part
> of the process of trying to put the PSU in without any vibrations.

No evidence the the PSU has anything to do with the problem.

> It's also good to check all possibilities.

He's done that by trying another power supply.

> Especially when it takes 0 seconds longer to check it.

Complete waste of time when he has already tried a different power supply.

>>> A friend had a similar problem, I think with the power supply.
>>> We found that putting some tissue paper between the power
>>> supply and the case stopped the noise. Maybe it secured it
>>> better and stopped the vibrations.

>>> Lifting the case is causing some other changes that are stopping the
>>> noise. So you have to experiment with moving things, holding things,
>>> not holding things, squeezing things. Move PSU from a position
>>> where there is noise(screwed in case as it is currently), to a position
>>> where there is no noise, finding the dfiferent ways. Move from a
>>> position of no noise(e.g. psu out of case), gradually trying to
>>> secure the psu, until yju suddenly find noise, then you've foudn a
>>> trigger. Hold it in place with your hand in te air. Then against
>>> the case. Then with tissue paper between it and the case, with
>>> screws in securing the PSU.

>>> It's possible that there's something knocking the fan inside the PSU.

>> Nope, you wouldnt get that warmup effect with that and you
>> wouldnt get the same effect with two completely different PSUs.

> That statement you just wrote is only relevant
> to the last sentence of mine that you quoted.

That is why I interleaved my comments,
so I can comment on particular bits of yours.

> The rest of what I wrote deals with the vibration possibility.

Yes, and I didnt comment on those comments of yours about
the vibration, JUST pointed out that the problem wont be due
to something rubbing up against the fan in the PSU, because
that wont happen with two completely different PSUs.

> And to the possibility you like to attack - of it being
> the PSU, what I already wrote in this post applies.

No it doesnt, because he wont have got that
effect in two completely different PSUs, and
you dont see that lifting effect with a PSU either.

The vibration problem is elsewhere in the case

> i.e. he'll find out if it was the PSU, in 0 seconds.

He's already found out by trying a different PSU.

> If it is,

No possibility what so ever of it being that, because
he has already tried a completely different PSU.

> then he'll have to cosndier opening up the PSU.

Taint gunna happen.

> It that possibility were to take time, or wasn't part of the
> more likely, vibration check, then i'd have said "if vibration
> check fails... try the following less likely possibility ...."

Its completely pointless considering the PSU because he
has already tried a completely different PSU and has got
the same effect, the noise goes away once the system
warms up and he gets the lifting effect when its cold.

>>> You could open the PSU and move any cable away
>>> from the fan. It could be nothing to do with the PSU,
>>> it could be that a cable is wacking a case fan.

>>> Regarding opening the PSU
>>> 2 issues to take into account so as not to hurt yourself
>>> * It must be unplugged. Then you won't get electricuted
>>> seriously. So that big fear can blow away.

>>> * That risk above was the big risk. The only risk now is not too
>>> bad. It's the charge in the big capacitors, and you touching a big
>>> capacitor. They , according to googling, will hurt your finger if
>>> you touch them and give you a shock, but probably not much more.
>>> You might want to wait for them to discharge. A day maybe to be
>>> safe, i'm not an electrician. But if you just open it to check a
>>> cable - the fan cable presumably, then you wouldn't be touching
>>> them. I think they're covered by a metal thing anyway like a
>>> homeless shelter for capacitors.

>>> And if you're really worried, use your right hand. so electricity
>>> travels down your right side, missing your heart which is on the
>>> left side.

>> Makes a lot more sense to not put your hands
>> inside the power supply with it plugged in.

> I said it must be unplugged - in the first risk - which was the main risk.

So there was no point in that last bit about using your right hand.

> Even when unplugged, you could still have
> the charge in the capacitors. (second risk)

Nope, they have bleed resistors across them.