Perhaps the MB temp is not really the chipset temp after all.
So do I think. When I simply unplug the fan (while the system is idle),
the heatsink (and the fan itself) become almost too hot to touch,
which should be 50 degrees C or slightly higher.
(Is this what they call "hot plugging"? Just kidding.)
But ASUS Probe says the the 'MB' temperature is 32 deg. C.
And the temperature readout does not change noticeably when
the fan is plugged back in.
It would be nice if the fan could be controlled, but it appears that
there is no built-in temperature sensor for the chipset.
SpeedFan tells me that there are five temperature sensors that
read out a sensible temperature (between 0 and 100 deg. Celsius).
One is the HD, one is the CPU, and one matches the 'MB temperature'
value that ASUSprobe displays.
Then there is another one that looks like a case (mobo surface)
temperature. The last one, advertised as 'ACPI', is suspicious.
It is constant at 40 deg. C.
None of these temperatures reacts to cutting the fan power.
Also, steering the chipset fan power seems to not work.
Again, SpeedFan tells me that there three fan speed control variables
(or whatever they are called), pwm1, pwm2 and pwm3.
It also tells me about three fan speed sensor variables,
fan1, fan2 and fan3.
(SpeedFan detects several more control and sensor variables
on the nForce SMBus, but none of those seem to work)
Fan 1 monitors the CPU fan and works fine.
Pwm1 controls the CPU fan and works fine.
Fan 2 monitors the Chassis1 fan and works fine.
Pwm2 controls the Chassis1 fan and works fine as well.
This is the one that can be used to drive the chipset fan
because the connector is pretty close (the stock cable is too short, though).
In a post above, someone already said he did this.
Fan 3 monitors the Chipset fan and works fine.
Pwm3 does not seem to have an effect at all. Bummer.
The mainboard manual states that
"The ASUS Q-Fan function is supported using the CPU Fan
and Chassis Fan 1 connectors only." (p. 2-23).
This may mean anything from
"it works but if you use it you are on your own" to
"we have implemented neither a sensor nor a pwn driver for the other fans".
(The manual's credibility here is a little low anyway,
as, as someone alread mentioned, the manual also states
"The chipset fan is synchronized with the CPU fan.",
which is entirely not so, and rightly so.)
Does anyone know what a temperature sensor on the board looks like?