Strange power-up problem

I have a GA-7VT880-L motherboard. (Socket A CPU with VIA KT880
chipset). Recently it has developed a strange problem when powering
up:

Press the power button, and you can hear the power-up sequence
starting (CPU & PSU fans start, disks begin to spin up). After about 2
seconds, it just shuts down again. After that, pressing the power
button does nothing at all - the system is completely dead. However,
if I then switch off the PSU (it has an on/off switch), wait a while,
then switch it back on, the system will usually power up successfully
and can then be used fine. (Sometimes I may need to do the PSU on/off
cycle more than once).

I replaced the power supply and the problem persists, so I'm guessing
it's some kind of motherboard issue. The question is, does this sound
familiar to anyone and if so is there anything I can do about it? Or
do I just live with it until the time comes when it bothers me enough
to replace the mobo?

Clive Backham wrote:
> I have a GA-7VT880-L motherboard. (Socket A CPU with VIA KT880
> chipset). Recently it has developed a strange problem when powering
> up:
>
> Press the power button, and you can hear the power-up sequence
> starting (CPU & PSU fans start, disks begin to spin up). After about 2
> seconds, it just shuts down again. After that, pressing the power
> button does nothing at all - the system is completely dead. However,
> if I then switch off the PSU (it has an on/off switch), wait a while,
> then switch it back on, the system will usually power up successfully
> and can then be used fine. (Sometimes I may need to do the PSU on/off
> cycle more than once).
>
> I replaced the power supply and the problem persists, so I'm guessing
> it's some kind of motherboard issue. The question is, does this sound
> familiar to anyone and if so is there anything I can do about it? Or
> do I just live with it until the time comes when it bothers me enough
> to replace the mobo?

Sounds like there may be some defective electrolytic capacitors on the
MB. Usually the tall ones near the CPU socket, but they can be anywhere
on the MB.

Take a look at this web site; it will show pictures of bad caps.
They're generally easy to spot: the top may be bulging up, there may be
a brown colored material on the top, side, or bottom of a bad cap.

http://www.capacitorlab.com/visible-failures/index.htm

If you have bad caps, the best thing to do is get a new MB, unless
you're skilled at desoldering and removing the bad caps and installing
and soldering the new ones.

RobV wrote:
> Clive Backham wrote:
>> I have a GA-7VT880-L motherboard. (Socket A CPU with VIA KT880
>> chipset). Recently it has developed a strange problem when powering
>> up:
>>
>> Press the power button, and you can hear the power-up sequence
>> starting (CPU & PSU fans start, disks begin to spin up). After about 2
>> seconds, it just shuts down again. After that, pressing the power
>> button does nothing at all - the system is completely dead. However,
>> if I then switch off the PSU (it has an on/off switch), wait a while,
>> then switch it back on, the system will usually power up successfully
>> and can then be used fine. (Sometimes I may need to do the PSU on/off
>> cycle more than once).
>>
>> I replaced the power supply and the problem persists, so I'm guessing
>> it's some kind of motherboard issue. The question is, does this sound
>> familiar to anyone and if so is there anything I can do about it? Or
>> do I just live with it until the time comes when it bothers me enough
>> to replace the mobo?
>
> Sounds like there may be some defective electrolytic capacitors on the
> MB. Usually the tall ones near the CPU socket, but they can be anywhere
> on the MB.
>
> Take a look at this web site; it will show pictures of bad caps.
> They're generally easy to spot: the top may be bulging up, there may be
> a brown colored material on the top, side, or bottom of a bad cap.
>
> http://www.capacitorlab.com/visible-failures/index.htm
>
> If you have bad caps, the best thing to do is get a new MB, unless
> you're skilled at desoldering and removing the bad caps and installing
> and soldering the new ones.
>

The only comment I'd add, is the symptoms are showing "latch-off". The
computer is not recovering from the failure condition, until the
switch on the power supply is toggled to OFF and then ON again.
That clears the latched failure. A latching failure can occur on some
Vcore switching regulator designs (as RobV has observed). And some
power supplies can also do that (after an internal failure condition
is detected, they won't run until the power is toggled).

Since the power supply has been replaced, that leaves the motherboard.

Paul

Thanks to all who have replied. I've taken a look at the mobo and
don't see any obvious visible signs of a failed capacitor, but I know
that electrolytics can still look fine after they've gone bad.

I think I'll just live with it for a while until it gets too
irritating, then get a more modern mobo and CPU.

Funnily enough mine is doing the same thing and it is brand new. The board
is a GA X48T DQ6.
If i leave the computer for a period of time it goes into sleep mode (i
think). I have set the bios to wake up the pc with a left click of the mouse
button, but when i try to awake the pc it just cycles the power up on and
off.
The only way to prevent this with my limited knowledge is to just set up the
power management in control panel to be always on.

Phil.

"Paul" <> wrote in message news:g7tbih$jdl$...
> RobV wrote:
>> Clive Backham wrote:
>>> I have a GA-7VT880-L motherboard. (Socket A CPU with VIA KT880
>>> chipset). Recently it has developed a strange problem when powering
>>> up:
>>>
>>> Press the power button, and you can hear the power-up sequence
>>> starting (CPU & PSU fans start, disks begin to spin up). After about 2
>>> seconds, it just shuts down again. After that, pressing the power
>>> button does nothing at all - the system is completely dead. However,
>>> if I then switch off the PSU (it has an on/off switch), wait a while,
>>> then switch it back on, the system will usually power up successfully
>>> and can then be used fine. (Sometimes I may need to do the PSU on/off
>>> cycle more than once).
>>>
>>> I replaced the power supply and the problem persists, so I'm guessing
>>> it's some kind of motherboard issue. The question is, does this sound
>>> familiar to anyone and if so is there anything I can do about it? Or
>>> do I just live with it until the time comes when it bothers me enough
>>> to replace the mobo?
>>
>> Sounds like there may be some defective electrolytic capacitors on the
>> MB. Usually the tall ones near the CPU socket, but they can be anywhere
>> on the MB.
>>
>> Take a look at this web site; it will show pictures of bad caps. They're
>> generally easy to spot: the top may be bulging up, there may be a brown
>> colored material on the top, side, or bottom of a bad cap.
>>
>> http://www.capacitorlab.com/visible-failures/index.htm
>>
>> If you have bad caps, the best thing to do is get a new MB, unless you're
>> skilled at desoldering and removing the bad caps and installing and
>> soldering the new ones.
>>
>
> The only comment I'd add, is the symptoms are showing "latch-off". The
> computer is not recovering from the failure condition, until the
> switch on the power supply is toggled to OFF and then ON again.
> That clears the latched failure. A latching failure can occur on some
> Vcore switching regulator designs (as RobV has observed). And some
> power supplies can also do that (after an internal failure condition
> is detected, they won't run until the power is toggled).
>
> Since the power supply has been replaced, that leaves the motherboard.
>
> Paul