Power startup problem [Home Built PC]

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From: Gabriel Knight on 3 Jun 2010 13:02

Hi all, I have a old pc that im trying to boot, when I press the power
button it gets power for about 5 seconds and then turns off, this is not
long enough to see anything on the screen. I pulled out everything like
memory, HDD, CD rom, Floppy. It has an onboard speaker but I get no error
code beeps at all for the 5 seconds. I tried another power supply but the
same thing happens. I then replugged the original power supply in and now it
seems dead as it dose nothing when I press the power buttopn. Is this a
botherboard problem as in is it dead? I have looked at the big capacitors
(please ignore my spelling) on the mobo and one looks a bit bent out and
some brown residue is near it but just a little.

As far as I see there is no case sensor so it cant be that.

Please help..

Thanks
GK

From: Jan Alter on 3 Jun 2010 13:11

"Gabriel Knight" <FakeEmail(a)hotmail.com> wrote in message
news:ieRNn.900$Ls1.872(a)news-server.bigpond.net.au...
> Hi all, I have a old pc that im trying to boot, when I press the power
> button it gets power for about 5 seconds and then turns off, this is not
> long enough to see anything on the screen. I pulled out everything like
> memory, HDD, CD rom, Floppy. It has an onboard speaker but I get no error
> code beeps at all for the 5 seconds. I tried another power supply but the
> same thing happens. I then replugged the original power supply in and now
> it seems dead as it dose nothing when I press the power buttopn. Is this a
> botherboard problem as in is it dead? I have looked at the big capacitors
> (please ignore my spelling) on the mobo and one looks a bit bent out and
> some brown residue is near it but just a little.
>
> As far as I see there is no case sensor so it cant be that.
>
> Please help..
>
> Thanks
> GK
>

From your description my first inclination would also have been a bad PS.
However, I think you located the problem yourself, being bad capacitors. You
can read lots of information about replacing them but if the board is old,
and you're not into this for the shear 'fun' of it then it's simply better
to replace the motherboard. The only other thought I have is if you know for
certain that the substitute PS that you used was known to be good. Still,
one bad cap is enough to keep a mb from firing up.

--
Jan Alter
bearpuf(a)verizon.net

From: Paul on 3 Jun 2010 13:21

Gabriel Knight wrote:
> Hi all, I have a old pc that im trying to boot, when I press the power
> button it gets power for about 5 seconds and then turns off, this is not
> long enough to see anything on the screen. I pulled out everything like
> memory, HDD, CD rom, Floppy. It has an onboard speaker but I get no error
> code beeps at all for the 5 seconds. I tried another power supply but the
> same thing happens. I then replugged the original power supply in and now it
> seems dead as it dose nothing when I press the power buttopn. Is this a
> botherboard problem as in is it dead? I have looked at the big capacitors
> (please ignore my spelling) on the mobo and one looks a bit bent out and
> some brown residue is near it but just a little.
>
> As far as I see there is no case sensor so it cant be that.
>
> Please help..
>
> Thanks
> GK
>

If you have brown residue around the base of the capacitor, that
capacitor is bad.

Capacitors can leak from *either* end of the device. The pressure
relief seam on the top (like the letter "K" or an "X") can split
and release fluid. That is when you see the brown deposit on top.

The other end of the capacitor has a rubber plug in it. If pressure
builds up in the capacitor, the rubber will be pushed out enough
for the pressure to be released. Sometimes, this causes the capacitor
to lean on an angle. If you see the brownish or rust colored deposits
on the motherboard, the leakage may be coming from the bottom.

Do not continue to operate the motherboard, with bad capacitors.
You need to replace the capacitors, before there is more damage.
For example, if you forced the motherboard to continue running
some how (say, grounded the PS_ON# signal so the power could
not go off), what would eventually happen, is a MOSFET would fail
and burn up, or a toroidal or square inductor coil could burn.
Such components are a bit harder to replace, because of the
difficulty of figuring out what to replace them with.

So if you want to save the motherboard, you need to have the
capacitor replaced. If you can't replace the capacitor, then
you need another motherboard.

Paul

From: LSMFT on 4 Jun 2010 21:46

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