Weird CPU fan behavior on a Presario

  • Thread starter Thread starter Mr. Land
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Mr. Land

I searched but couldn't find anything like this...anyone ever heard of
such a thing?

A relative's Presario started giving a "CPU Fan Failed" error message
on startup. It doesn't do this every time, but seems to enter periods
of time when it happens.

I opened it up and watched it during powerup: when the system power is
first turned on, the CPU fan spins up to what appears to be normal
speed. Shortly afterwards, however, just after the motherboard "beeps"
that it has completed its POST, the RPM of the CPU fan drop way down
(almost like it's now running on about 4 volts instead of 12), then the
BIOS reports that the CPU fan has failed.

The fan has 3 wires on its connector - my understanding is that the
third wire reports the current fan speed to the motherboard. I have
some extra, similar, 3-wire CPU fans that I know are OK and tried
those...same behavior. I also tried disabling hardware monitoring for
the CPU fan in the BIOS...the fan still slows way down just after the
POST beep and the BIOS still reports it as failed.

When the BIOS reports this error, it gives the option of pressing <F2>
to continue. I've tried this, and subsequently run the box for hours
(with all covers on). Other than this pesky error the system appears
to run just fine.

Is this a defective motherboard?

Thanks for any ideas....
 
I searched but couldn't find anything like this...anyone ever heard of
such a thing?

A relative's Presario started giving a "CPU Fan Failed" error message
on startup. It doesn't do this every time, but seems to enter periods
of time when it happens.

I opened it up and watched it during powerup: when the system power is
first turned on, the CPU fan spins up to what appears to be normal
speed. Shortly afterwards, however, just after the motherboard "beeps"
that it has completed its POST, the RPM of the CPU fan drop way down
(almost like it's now running on about 4 volts instead of 12), then the
BIOS reports that the CPU fan has failed.

The fan has 3 wires on its connector - my understanding is that the
third wire reports the current fan speed to the motherboard. I have
some extra, similar, 3-wire CPU fans that I know are OK and tried
those...same behavior. I also tried disabling hardware monitoring for
the CPU fan in the BIOS...the fan still slows way down just after the
POST beep and the BIOS still reports it as failed.

When the BIOS reports this error, it gives the option of pressing <F2>
to continue. I've tried this, and subsequently run the box for hours
(with all covers on). Other than this pesky error the system appears
to run just fine.

Is this a defective motherboard?

Thanks for any ideas....
Click to expand...

Is the original fan a sleeve-bearing type and the system now
fairly aged? Well, I suppose even a relatively modern
system can have the fan fail in a couple years but it would
seem less likely with it throttling back to low RPM.

What is the amperage spec on the fan label? Typically when
a system has such an aggressive fan throttling it makes use
of a fan with a high RPM spec (@ 12V) so it has a larger
change in RPM relative to temp. If the fans you substituted
had a lesser RPM (or current rating, since the original
fan's RPM spec might not be available), then it might be
expected that they are not really suited for this control
method, will be running at lower RPM.

Because of this issue it is not yet clear of there is a
motherboard problem (that is, a "new" problem, it was a
questionable design if it operated on such narrow margin) or
simply that fan wear has resulted in too much RPM drop and
the other fans you substituted were simply not suitable as
replacements.

Either way, presuming the alarm never goes off until the fan
goes into a lower RPM range, the most cost effective
solution would be to simply make sure the fan RPM stays
higher. The two more common options are to either get a fan
with higher default (12V spec'd) RPM so it stays higher RPM
at the reduced voltage (or PWM control), or to get a fan
adapter than powers the fan from the 12V and Gnd lead of the
power supply plug but has an RPM lead and connector that
plugs into the motherboard. For this latter option your
target fan would be one with lower RPM than the original
since it would then be a constant speed fan never varied by
the motherboard.
 
Thanks for the ideas.

The system itself is only 2 years old. I can't tell you what type of
bearings the existing fan has - only that at first powerup it doesn't
seem to have any problem at all running at full speed.

The reason I suspected a motherboard problem in the first place was
that disabling the CPU hardware check in the BIOS seems to have no
effect - that is, even when the check is disabled, it appears to be
performed, yielding the error message.

Thanks again.
 
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