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

  • Thread starter Thread starter David Miller
  • Start date Start date
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David Miller

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?
 
David said:
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?
Click to expand...

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.
 
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
 
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
Click to expand...


This is a symptom of poor heatsink installation. The CPUs have
self-shutdown on over-temp. If you're sure you've put the HS on right
then it's probably the PSU.

Try stripping the system down to the minimum; Mobo, Video card, and
memory. See if you get a setup info on the screen. If that works but
adding things makes the system shut down you've got a crappy power
supply.
 
Hmm, well it would have been a possibility if it would happen every
time, but apparently it doesn't, that's why I ruled this out in the
first place... If the heatsink is installed wrong the cpu would overheat
-every- time it's switched on (which it doesn't, see the original post);
if the powersupply is weak, it will have trouble booting up if it can't
pull enough juice anymore to start everything up. This doesn't have to
happen all the time.

MC
 
Hmm, well it would have been a possibility if it would happen every
time, but apparently it doesn't, that's why I ruled this out in the
first place... If the heatsink is installed wrong the cpu would overheat
-every- time it's switched on (which it doesn't, see the original post);
if the powersupply is weak, it will have trouble booting up if it can't
pull enough juice anymore to start everything up. This doesn't have to
happen all the time.

MC
Click to expand...


I missed the original post. I'd swap the power supply. I've seen
really strange problems that were solved by a new PSU.
 
David Miller said:
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?
Click to expand...
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.
 
Al Dykes said:
I missed the original post. I'd swap the power supply. I've seen
really strange problems that were solved by a new PSU.
Click to expand...
Great I will give this a try... It was time to change anyhow since I'm
about to upgrade my processor and vid card anyhow

Currently I've got
300w PS
Athlon 1ghz processor
512 mb PC2700 DDRAM
GeForce MX200


I'm planning on moving up to a Athlin XP 3000 or so and get a GeForce
FX5700. Will have to get a 400 or 450 PS anyhow for that.

Thanks everyone!
 
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