CPU fan control problem on KT3 Ultra 2 mobo

The response below was sent to me by Mats Fredriksson after an initial post
in this newsgroup in early januari. I am posting this reply on his behalf.
Very useful information indeed.

<quotation>
Hi,
I read about your MS-6380E ver 1.0 problem on the following link:

http://www.motherboard-forum.com/msi/CPU_fan_control_problem_on_KT3_Ul..._2_mobo

I too have the same problem and have spent all weekend investigating why I
can't lower the CPU fan speed.
My conclusions so far:

1) CPU fan speed correctly monitored by several utilities + bios (just like
you found out).
2) The Winbond W83697HF chip used supports PWM regulation of 2 fan speeds.
3) The MSI KT3 Ultra mobo manual states that fan control is possible (note 2
on page 2-16).
4 ) Looking at the sample schematics for the Winbond chip, I see that the
three pin cpu fan header
pins Sensor , +12v and GND have the functions the pin names suggest.
5) If the fan speed is to be controlled then must the so called '+12V' pin
not be
connected directly to 12V but instead to a transistor driven by the PWM
output on the Winbond chip.

BUT..... Unfortunately it does in fact seem to be directly connected to 12V
!!!! I simply hooked up my ohm-meter and got zero ohms between all of the
+12V pins on all of the headers !! If fan control was implemented then
should the cpu fan header '+12V' not give a zero ohm reading (unless the
driving transistor is broken and short circuited internally).

I hope be able to get this verified by MSI, but if I am right then I can
only see 2 solutions:

1) Patch the board to implement the fan speed control (1 mosfet, 1
transistor, 4 resistors,
1 capacitor, 1 diod). If done probably best to create a small separate board
with all the
parts and a new fan connector and hook it up with the mobo (all signals
except the
PWM output on the Winbond chip are already available the CPU fan header). I
am NOT
recommending this approach !! (might damage board, hard to find right pin on
Winbond,
the effort not worth the $30 for a new fan).

2) Simply accept the fact that the board can NOT control fan speed and
instead replace the CPU fan with one with built in temperature controlled
speed.

I just installed an Artic-Cooling Copper Silent 2TC (I bought it for $30).
It is quiet and runs at approx 2000 rpm (at CPU temp 45°C) when my AMD
athlon XP 1800+ is not performing too heavy tasks.
My old Cooler Master fan ran constantly at 6200 rpm and made a lot of noise
(the sound absorbing
foam sheets I installed on all inner case surfaces, did not help much).

The Artic-Cooling fan connector connects directly to the CPU fan header, and
still provides the RPM information to bios and other utilities.

NOTE: I had to disable the 'CPU Fan Detection' in the bios to be able to
boot, else I got the 'boot attempt' led indication and beeping. My guess is
that the fan speed is too low when the new temperature controlled fan is
probed during boot. I am running PC alert in background so it will warn me
if the temp rises to much.

I am as of today not participating in any news groups, so that is why I am
sending you my findings directly to you. You may though pass on my findings
to the forum. Please leave out my email adress if you do so.

Good luck, Mats Fredriksson
</quotation>

--
jan a.m. van mastbergen