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on power up, CPU fan spins 1 sec then everything stops

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Anonymous
a b B Homebuilt system
a b à CPUs
January 7, 2005 2:53:32 AM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

I've had this proble sporadically and don't know how I've fixed it but its
not stopping so far tonight.

When I hit the case power switch I see the CPU fan start to spin up and then
it stops. No error beeps or anything.

Any subsequent hitting of the power switch doesn't have any effect until I
disconnect the power cord and plug it back in again. Then its the same
thing.

I've tired replugging in all the connectors and everything but no change.

What could this be a symptom of? Could it be a power supply failure?
Anonymous
a b B Homebuilt system
a b à CPUs
January 7, 2005 10:39:01 AM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

David Miller wrote:

> I've had this proble sporadically and don't know how I've fixed it but its
> not stopping so far tonight.
>
> When I hit the case power switch I see the CPU fan start to spin up and then
> it stops. No error beeps or anything.
>
> Any subsequent hitting of the power switch doesn't have any effect until I
> disconnect the power cord and plug it back in again. Then its the same
> thing.
>
> I've tired replugging in all the connectors and everything but no change.
>
> What could this be a symptom of? Could it be a power supply failure?
>
>

Symptom of a short in the system somewhere or an
overloaded/defective/under-rated PSU.

Excessive current causes the PSU over-current protection to kick in,
shutting down the PSU, and it takes an AC mains power cycle to reset the
OCP circuit.

Cheap PSUs are seldom, if ever, capable of handling the power suggested by
their generic rating. e.g. an el-cheapo '450 Watt PSU' won't handle 450
watts. But then, you gave no clues at all as to what your system or PSU is.
January 7, 2005 10:58:22 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

Hi David,

This sounds to me like a classic case of failing or too weak power
supply. I've seen this happen more often with pc's, and every time
changing the PSU fixed the problem. With some it wouldn't even spin just
"twitch" the fan, nothing more, then quit and be dead :p 

Hope this helps!

MC

David Miller wrote:
> I've had this proble sporadically and don't know how I've fixed it but its
> not stopping so far tonight.
>
> When I hit the case power switch I see the CPU fan start to spin up and then
> it stops. No error beeps or anything.
>
> Any subsequent hitting of the power switch doesn't have any effect until I
> disconnect the power cord and plug it back in again. Then its the same
> thing.
>
> I've tired replugging in all the connectors and everything but no change.
>
> What could this be a symptom of? Could it be a power supply failure?
>
>
Anonymous
a b B Homebuilt system
a b à CPUs
January 8, 2005 10:58:09 PM

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

"David Miller" <scorpioatl@comcast.net> wrote in message
news:p M2dnQzj6LdTiEPcRVn-2w@comcast.com...
> I've had this proble sporadically and don't know how I've fixed it but its
> not stopping so far tonight.
>
> When I hit the case power switch I see the CPU fan start to spin up and
then
> it stops. No error beeps or anything.
>
> Any subsequent hitting of the power switch doesn't have any effect until I
> disconnect the power cord and plug it back in again. Then its the same
> thing.
>
> I've tired replugging in all the connectors and everything but no change.
>
> What could this be a symptom of? Could it be a power supply failure?
>
Very likely. I've seen exactly the same symptoms a number of
times in the past, except that they were not sporadic. In every case,
the +5V line had failed. The fan is powered by the 12V rail which
is still OK and the fan turns for a moment, but then the PSU's
own monitoring system detects the absence of the +5V line and
shuts down.

As long as the power connector is plugged in, the separate
standby supply is still operating and is still powering the
fault-monitoring section which keeps the main power off.

In your case, the +5V rail may be failing intermittently,
perhaps due to reasons other than a dead rectifier which
was always the reason in the cases I saw. Perhaps a bad
solder joint inside the PSU.
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