CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

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Motherboard: Foxconn N570SM2AA
CPU: AMD Athlon 64 x2 5600+ AM2

The CPU has a 4-wire fan (black, red, blue, yellow).  The "CPU Fan"
header on the mobo only has 3 pins.  Using the polarization on the
connectors, the black, red, and blue wires would get connected while
the yellow wire would hang off by itself and not be connected.  From
what I can tell, the 3 wires that would get connected are power,
ground, and sense.  It would be the PWM (pulse-width modulation) wire
that wouldn't get connected.  That means there would be no control on
the speed of the CPU fan.  The assumption is that without this
control, the fan would constantly spin at its highest speed but others
have noted that without the PWM line connected means the fan might
spin at high (noisy), medium, or low speed - and low would probably be
too little to properly cool the CPU.

The mobo's manual shows a 4-pin header for "CPU Fan".  That is NOT
what is on the mobo which only has 3 pins.  Next to the 3-pin "CPU
Fan" header on the mobo is a 4-pin "J4" connector.  It is bare (just
the 4 pins in a row and no plastic polarizing body).  The J4 connector
is not mentioned in the hardcopy of the manual included with the mobo
nor in the online copy of the manual.  So while J4 has 4 pins with no
polarizing plastic body and is next to the 3-pin "CPU Fan" header, I
haven't been able to determine is that is where I plug in the 4-wire
CPU fan.

For a picture of the mobo, look at:


It shows a 4-pin header for the CPU fan.  What I actually got on the
mobo is a 3-pin header marked "CPU Fan".  The pictures are lying.  The
specification for that mobo says that it supports 7 (seven) internal
SATA ports and which I have.  There are only 6 shown in the picture.
If you look closely at the picture, up by the 4-pin Molex connector on
the mobo is a square chip and right by it are solder pads for the 7th
SATA port missing in the picture but is on my mobo.  Also, the specs
say there are 3 internal USB headers, not the 2 shown in the picture
(the 3rd is where the solder pads are in the lower left of the
pictured mobo).

Remember the "J4" labelled 4-pin header that I mentioned might be a
possibility for connecting the 4-wire CPU fan (just a guess, though)?
Nope, it's not in the picture but the solder pads are there in the
picture (to the right of the *pictured* 4-pin CPU Fan header and
underneath the tall black heatsink).

Apparently when Foxconn decided to upgrade this mobo to add the
missing connections (since the chips were probably already there) they
chose to change from a 4-pin CPU Fan header to just a 3-pin header.
That sucks.  Now I have to figure out if I want to return the mobo to
Newegg and find a different one or figure out how to get the PWM
function of the 4-wire CPU fan to work with a 3-pin header (or find
out what the undocumented J4 4-pin header is for).

Re: CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

On Sat, 15 Dec 2007 09:54:36 -0600, "VanguardLH"

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Without the PWM wire, yes the fan should rotate at full
speed.  Generally the blue wire is the PWM wire so it is odd
that yours shipped with this blue wire in the 3rd pin
position and the yellow in the 4th position.  Maybe they
swapped the colors, or maybe the wires were inserted in the
wrong plug holes.

Looking at the following picture,

Left to right are PWM, RPM, ~ 12V, Gnd.
If you find your fan doesn't give an RPM reading as the plug
is currently configured, take a needle and depress the
connector tab through the slot in the side of the plastic
plug to pull out the blue and yellow and change their

Although the picture shows blue, green, yellow, black, some
fans instead use corresponding blue, yellow, red, black.
Black is a pretty safe bet, is ground.  You can manipulate
the other wires till you find the power and RPM output if

If you have a multimeter you can probe the mystery 4 pin
header to find whether it has ~ 12V and ground pins in the
expected locations then if it does, as above you can try
pulling the fan into it.

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Yes they will.  While some fans supposedly aren't as
tolerant of power-pin PWM control as others, they can
generally be used this way.

Re: CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

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With the capacitor across the fan, it doesn't seem that a square pulse
would be applied to the fan but instead a ramp up voltage.  I'm
assuming the cap discharges before the next pulse (on state).  My
guess is that they don't want a high current in the winding of the
motor in the fan which could burn it out when it hasn't started moving
yet or is just getting pulsed to speed up again.

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I've been using SpeedFan in my latest host since it came out, and it
replaced MBM (MotherBoard Monitor).  Don't know how many years that
I've been using those programs but I have yet to replace a CPU fan.
Fact is, I would prefer having to replace the CPU fan after several
years rather than have to constantly listen to the high noise with it
spinning always at full speed but when it provides no additional
cooling (i.e., when the CPU temperature won't go down after exceeding
a certain RPM).  The BIOS will slam down the CPU if it gets too hot so
I'm saved and will then have to replace the CPU fan.

Many folks are deluded into thinking they need their CPU running at
its absolutely attainable lowest temperature using the current cooling
method.  They forget that the CPU is rated for continuous operation
at, say, 80C but they've been told to get it somewhere around 45C.  I
have seen some that became unstable at 60C.  I have Speedfan
configured to pulse the CPU fan at 5% duty until it gets to 55C where
it will then up the fan speed to get it below 55C and alert me if the
temperature exceeds 60C.  Fact is, for my setup, I know it will run
reliably at 72C but I'd prefer a safety margin.  It only hits 55C when
I'm playing a game but the noise of the game swamps the noise of the
increased RPM of the fan; else, I'm so into the game that I don't
notice the increased fan noise.  Of course, whether I can continue
using Speedfan depends on whether it recognizes the controller in my
new host.

Thanks for the links.  Makes for some interesting reading.  Hopefully
the 4-wire fan connected to the 3-pin header (which means power,
ground, and sense are connected but not the PWM wire) will have the
CPU fan always spinning at its max speed - until I get around to
replacing it.

Re: CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

VanguardLH wrote:
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It could be, that J4 is a programming header for an adjacent serial EEPROM.
There is an IRDA header further over, but I take it that isn't the one
you're looking at. The pictures I have available, aren't clear enough
to say much. (A header without keying, is probably not a good
way of driving a fan, because if the customer rotates the connector
180 degress, stuff will get burned as a result.)

I'd just stick the 4 pin fan onto the 3 pin CPU header and try it out.
If the fan is "cooling too well", and it seems you could run it slower,
I'd use a FanMate II to slow the fan down. The FanMate II can handle
about 0.5 amps or so, so check the fan label to see what kind of
current it draws, and whether it is under that limit, before using the
FanMate II. (Note - get a recent copy of Prime95 and run the Torture
Test, as a means of simulating maximum CPU heating. If prompted to
"join", you don't have to join the Mersenne project to use the
Torture Test function.)


The only potential problem I see with the FanMate II, is it looks like
it has three pin connectors on either end of the cable assembly. You'll
have a problem connecting the four pin CPU fan, to one of these, as near
as I can tell.


To convert a "safe" shrouded three pin connector, to a "dangerous"
exposed three pin, use one of these. This will allow the four pin
AMD fan, to plug to the unprotected three pin male end. You would use
one of these on the end of a Fanmate II cable, to fit the AMD fan.


The Foxconn people have shown, time and again, they are "just a manufacturing
plant". There aren't any brains running the place, and considering the
customer's point of view. Just a huge "Easy Bake Oven", churning out


Re: CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

VanguardLH wrote:
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This article is from Intel and is specifically about their motherboards
but it should apply equally to others:


If your motherboard supports fan-speed control on the 3-pin connector
then it should work with your 4-pin fan. The method used will be
different and possibly not so precise but it should still work.

John McGaw
[Knoxville, TN, USA]

Re: CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

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Thanks for the article link.  Be nice if they showed what color was
each wire.  Presumably the polarizing plastic body is how the plug and
header are to be oriented (i.e., black, red, and blue are connected
and yellow hangs off unconnected).  Hopefully without the PWM wire
connected the fan will rotate at maximum speed.

I'm using Speedfan on mobos where there are only 3 wires on the fans.
Since this also uses PWM to control the duty cycle of the fan, I have
to wonder how it works.  Is the PWM applied against the power supplied
to the fan (i.e., by applying a duty cycle on the power input to the
fan)?  If so, I wonder if these 4-wire fans with a separate PWM wire
will handle PWM on their power wire.

Re: CPU fan has 4 wires. Mobo header has 3 pins. Suggestions?

VanguardLH wrote:
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This is the description of Intel's fan. This may be different than
how the AMD Athlon64 retail one works. (I hate the AMD site enough
now, that I don't dredge for tech info there any more.)


   "This active thermal solution does not support variable voltage
    control or 3-pin PWM control. If this fan is plugged into an older
    3-pin connector the fan RPM will default back and then be controlled
    by the thermistor located on the fan. When operating in thermistor mode,
    the fan speed will vary based on the inlet (T-inlet) temperature
    located at the fan."

But I believe Asus motherboards in the past, have supported both
control methods, and they were selectable in the BIOS. (Voltage control
or PWM fourth-pin control.) Later boards seemed to drop the three pin
method, which means they'd only have the fourth-pin control. I don't
know what the history is for other manufacturers.

I think Intel doesn't want the +12V pin voltage varied, because
of the danger that the high side MOSFET won't saturate properly,
leading to a high thermal dissipation situation in the MOSFET.

Page 29 here, shows the old style three pin control method. I think
this is a PWM, but applied via transistor and cap to the 12V supply
pin on the fan.


And page 2 here, shows two diagrams for what is inside the fan.
The four pin fan has a MOSFET on the high side, which modulates
the coil current directly. One reason that the PWM operates at
25KHz, is so this method won't be audible on the four pin fan.



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