q_q_anonymous@yahoo.co.uk wrote
> Rod Speed wrote
>> 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.

> Running the PSU out of the case is a more sensible test,

Irrelevant when he has ALREADY tried another power supply.

> and it'll be done anyway.

You have absolutely no idea what he will do.

> I would use the results of that one,

More fool you when he has ALREADY tried another power supply.

> since we're unavoidably doing it anyway.

Wrong again.

> In practice, there are times when one makes assumptions that are
> quite reasonable to make, in narrowing down a problem, and then
> you hit a wall, and on reevaluating it from scratch with a fresh mind,
> you realise one of the assumptions is wrong. It is very rare that a
> fair assumption proves wrong, but it happens sometimes.

Waffle when he has already tried a different power supply.

THAT PROVES THAT IT CANT BE THE POWER SUPPLY.

> In his case, there's a slight chance that both PSUs have the
> same problem of rattling inside from the wire hitting the fan.

Nope, doesnt explain the lifting effect.

> And when he lifts the case it moves that cable a bit.

Mindlessly silly with two different power supplys.
They wont both have that very unusual fault.

> And there may be unforeseen issues too
> that cause one to question assumptions.

Not in this particular case where he has already tried
two different power supplys, and sees that lifting effect.

> So i'm not going to jump into assumptions.

You're a fool if you cant manage to grasp that there
is no assumption involved once he has tried two
different power supplys and he has that lifting effect.

> It's good to double check, and choose your tests carefully.

Nope, not in this particular situation. Its only worth doing that if
he has eliminated any possibility of the noise being due to the
case and didnt see the lifting effect. THEN it would be worth
eliminating the very unlikely possibility that two completely
different power supplys have the same quite rare problem.

> And when looking at possible problems,solutions and tests,
> it's a good idea to double check, especially if a double check
> takes 0 seconds(it being patr of another necessary check).

Mindless waffle in this particular situation.

> I'll give you one of the rare examples where I've made an
> assumption - or rather assigned a wrong probability (since
> I am willing to revaluate from scratch with a fresh mind
> ignoring assumptions. Since one is only human. ).

Irrelevant to what makes sense in this particular situation.

<reams of irrelevant crap flushed where it belongs>

> What you are doing, is making assumptions absolute.

Wrong, there is no assumption what so ever involved
in the particular diagnosis being discussed.

> I might find myself saying "I find it hard to believe that this
> is the problem..." or "this is most likely, this is unlikely".
> And I do rule things out.. But not permanently. And in
> deciding tests and possible solutions, I look at how much
> time they'll take. If it's a great test and it takes 0 seconds,
> i'm all for it. And i'm not against doing it twice to be sure!

More mindless waffle with the particular problem being discussed.

>>>>> 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 method is snippnig and interleave.

Nope, I didnt snip a thing. I usually dont snip.

> It applied here.

Nope.

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

>> Nope, they have bleed resistors across them.

> And out of interest, were these 'bleed resistors'
> also on all old AT power supplies and All ATX PSUs?

Irrelevant with the ATX PSU being discussed.