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, and it'll be
done anyway. I would use the results of that one, since we're
unavoidably doing it anyway.

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.

In his case, there's a slight chance that both PSUs have the same
problem of rattling inside from the wire hitting the fan. And when he
lifts the case it moves that cable a bit. And there may be unforeseen
issues too that cause one to question assumptions. So i'm not going to
jump into assumptions. It's good to double check, and choose your
tests carefully. 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).

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. ).

I had 2 computers hooked up to a DSL router/modem. One of them, I
never had any problems with the internet connection. The other one,
the internet connection kept going from time to time, then coming back.
Every time, I checked the other computer, saw that it was fine. The
router configuration is ok, it hasn't been changed. There's no in built
firewall in the "router" misconfigured.
So I figured that the router is fine(working), since one of the
computers gets to the internet with it.
I tried plugging the "computer that worked" into different ports, and
it still worked. So that double checked that the router is fine, in all
ports. It was really looking like it was this one computer that was
the issue.
To narrow things down fast with that one computer, I booted knoppix,
and got no internet connection (usually i would). So, it wasn't a
broken software firewall on the computer blocking the connection.
I tried a cat5e cable from the working computer, and it worked in the
other one, but then I lost th einternet connection again. Put it back
in the working one and the working one was fine.
This was narrowing down to the NIC in that "computer that wasn't
working".
I replaced the NIC, and got net access for 5 minutes, then failure
again.

I started getting bothered, because I could continue testing this, but
it is not a good possibility , infact the only possibility that I could
think of, and the most likely, that - and this is strange - that the
computer was assassinating my NICs. Could be a bad PSU, could be a bad
MBRD.. I don't want to keep trying new NICs in that computer and
potentially having them assassinated.

So I quite looking at the problem. After about a week, the "working
computer" suddenly failed to get an internet connection through the
router!! Then I got suspicious that the router was at fault!
I had an old router which I had declared broken but left it in the
shelf incase it had any life in it after being left around for years,
in the desparate event that i'd have to bother trying to use it. It
worked for about an hour!! And gave all my comps internet access. So
I went out and bought some new working routers - with warranties , from
my ISP!

So there you see a good example. Everything pointed to the router
being fine. My checks and double checks that I described. (though I was
limited, not having another working router to try). It really looked
like the NIC.. But that turned out wrong.

What you are doing, is making assumptions absolute.
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!




>
> >>> 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. It applied here.

<snip>
> > 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?