New CPU fan not working

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When I booted up my computer the other day, I got the message
"CPU fan has failed" and it shut back down. Today I bought a
new fan, and installed it. It still does not work!  :crybaby: My
husband took the old fan and hooked it to a battery and it worked just
fine, it just won't work in the computer. Someone please tell me what
is making the fan not work...I work from home and can't function
without my computer.

Re: New CPU fan not working

Hi, noted it's your first post so welcome.

Testing the fan on a battery should have been the first step, it don't
take too much to clog them up with dust. One good test is to note if
any other fans are running... ie case fans etc because this would
indicate that the 12 Volt dc supply is ok.

These fans usually runs from the 12 volt supply from the PSU (power
supply unit for short) sometimes usually via a regulator transistor or
IC on the mobo so really the PSU needs to be the next thing to check.

If you could borrow an identical one just to plug and try would be

We need to know if the PSU is delivering the 12 Volts DC, without a
test meter the only way is to try another power supply.... but it's
alright dashing out buying a new power unit if we know this is the
problem, because it could easily be the mobo or 'maybe' the cpu itself
especially if the fan has been stopped, but there is usually some form
of protection around to prevent CPU thermal damage.

It would be wise is to check that the wiring from the power unit to
the mobo has'nt been disturbed... it does happen that the crimps in
the molded plug become's loose or even the connectors themselves.

Also while delving in there, look for swollen capacitors where the
tops have 'domed', they should be nice n' flat .... and not leaking
any gunge.


Re: New CPU fan not working

momx5 wrote:
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OK, this cable is what you want. As far as I can tell, there are
two cable assemblies in this package, which is hard to see in
the picture.

That cable consists of three connectors. A female fan header, a male
fan header, and a four pin Molex disk drive connector. The cable
draws power for the fan, from a disk drive cable. So if the motherboard
header power source is burned out, that cable can bypass the power
problem, and allow the fan to run.

The female fan connector has the RPM wire on it. When you plug in the
female connector, to the CPU fan header, that is how the motherboard
will get the RPM signal that tells it the fan is spinning. So that still
has to be plugged in.

This is essentially what the cable does.

      Molex 1x4                                     Male 3 pin (plug fan
                                                                into this)
       12V  --------------------------------------- Fan +12V
       GND  -------------------------------+------- GND
       GND  --X                            |  +---- RPM
       5V   --X                            |  |
                                           |  |
                                           |  +---- RPM
                                           +------- GND
                                                X-- Fan +12V

                                                    Female 3 pin (plugs to
                                                    CPU_FAN motherboard header)

In the above figure, I rearranged the pins on the fan connectors, to make
it easier to see the wires. The fan pinout is *not* as shown above. Check
the motherboard manual, to see the actual order of the fan pins.

Second note, I drew the wire assembly, as I see it in the Newegg picture.
In fact, the GND wire running between fan headers is not needed. I have
one cable assembly like the above, that has a single white wire running to
the female connector.

Third note, there are other versions of this assembly available. There
is one that has two Molex 1x4 connectors on the left hand side of the
picture. That one allows these adapters to be "stacked" or "daisy chained"
so you don't lose the use of the Molex drive connector. If the
computer in question is low on Molex drive connectors (say the computer
is a Dell/HP/Gateway, and there happen to be no spares), you can
buy a "Y" cable for disk drive connectors, and that will give a second
connector for use with the above cable.

So the purpose of the above fan adapter cable assembly, is to:

1) Power the fan from a disk drive connector.
2) Feed the RPM signal to the CPU_FAN header.
3) To be used, if the power dies on the CPU_FAN header.
4) Or can be used, if a fan draws more current than the fan header can
    provide. For huge fans drawing 1 amp, an adapter like this will
    protect the fan header from burnout.


Re: New CPU fan not working

On Wed, 31 Jan 2007 11:48:12 -0000, no@spam.invalid (momx5)

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It means the fan RPM signal was too low (Or not read).  The
fan might work but spin too slow now due to a progressive
failure of the bearing.  Similarly, the new fan might also
spin too slow to be detected properly- some motherboards
can't properly detect very low RPM fans, OR it could be that
the replacement fan does n't have an RPM signal output (3
wires going to the fan header on the motherboard).

It might be possible to enter the bios and turn off that
shutdown-on-failed-fan setting, though ideally you'll supply
us with more info about which of the above possibilities
seems probable, or if none of them, other related info to
help determine the cause.

Re: New CPU fan not working

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The fan appears to be OK, so of there another 3 pin connector on the
motherboard you can plug it into try it - there are usually a few. If so and
if it works in there, I would go into the BIOS and disable the shutdown on
CPU fan failure and enable the shutdown on CPU temperature setting -
assuming you have these settings. If the fan doesn't work on another (or
any) of the motherboard connectors, then either the motherboard is failing
to power these connectors or the power is insufficient to start the fan
spinning in which case - give it a good clean and see if that helps (might
be that the test battery might have had a higher ampage - more power at the
same voltage).

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