Cannot slow down Scythe fan despite undervolting

Munters · Post by **Munters** » Fri Oct 24, 2008 12:58 am

I've got a Antec Solo case equiped with 2 Scythe KamaFlex 92mm intake fans, and replaced the TriCool with a Scythe 120mm SFF21E fan.
For CPU cooling I use a Scythe Mine rev.B, with fabric installed 100mm fan.

All Fans are connected to the motherboard via an extra 3-pin cable with internal resistor for a 12V -> 10V drop, and additionaly I enabled Q-Fan for a further temp-based reduction on the Asus p5q-E motherboard.
All three case fans do spin ~700 rpm now. (A 24 h stress test showed a 900 rpm max, so q-fan seems to work fine).
The PSU fan (Enermax Modu82+) runs below 500 rpm, and the GPU is cooled passive btw.

Now the problem: I cannot slow the CPU cooler fan. This is the fabric installed Kaze-Jyu SY1025SL12M, running 1500 rpm.
No mather the voltage I feed to this fan, it always spins at 1500 rpm!
Enabling Q-Fan and using the cable-with-resistor (I even tried two of them in series) this fan always spins at 1500 rpm.
(If I disconnect the fan completely, the hardware monitor shows correct 0 rpm, so I'm monitoring correct.)

Has anyone have a clue why this fan neglects all undervolting, and is able to run at its full speed?
Thanks!

Post by **NeilBlanchard** » Fri Oct 24, 2008 3:52 am

Hello & welcome to SPCR!

Are all the fans connected to the same header? If you run with just the CPU fan connected, does it work then? Does the Q-Fan control work on more than one fan header?

xan_user · Post by **xan_user** » Fri Oct 24, 2008 7:16 am

what happens if you swap headers? lots of mobo oems seem to think only one header should be controllable. Why this is no one really knows.

dhanson865 · Post by **dhanson865** » Fri Oct 24, 2008 11:02 am

Any fan you plan to control by software or bios shouldn't be going through a special cable with a resistor or any kind of voltage change. Feed it 12v and then use the software to control it.

Munters · Post by **Munters** » Mon Oct 27, 2008 7:40 am

All three case fans are connected to their own 3-pin motherboard connector. The q-fan setting in the bios can be dis/enabled for all three at once. This works fine (even with the additional resistor-cable).

The cpu fan is connected (with a 3-pin connector) to the 4-pin connector on the motherboard.
The bios has its own q-fan setting for this connector.

If I connect the cpu fan to a case fan connector, it runs silently at about 900 rpm.
If I connect it to the cpu fan connector, it runs at 1500 rpm only (this is the default speed of this fan).
Enabling/disabling q-fan doesn't do anything. No mather if I use the special cable-woth-resistor.
Also the cable-with-resistor alone doesn't do anything either. No mather the q-fan setting.

Maybe 1500 rpm for a cpu fan is the bottom setting for q-fan. I don't know if this is the case, I can understand however.
I do not understand why the special cable doesn't work however.
(This little cable does work correct, I switched them with a cable which I used for a case fan).

Post by **NeilBlanchard** » Mon Oct 27, 2008 8:47 am

Hi,

It may be that since the CPU fan header is a 4-pin, that it may only work with a 4-pin (PWM) fan?

Munters · Post by **Munters** » Mon Oct 27, 2008 12:38 pm

Possible, it is not described in the manual however.
Also it does not explain why the fan still runs full speed while getting only 9,5 V (it's a sharkoon 12V -> 9,5V mod cable)

Munters · Post by **Munters** » Thu Oct 30, 2008 1:49 pm

Problem solved!

Q-Fan on the cpu does work with PWM only on this board indeed. Whereas you could change the control into DC control on older Asus boards, this isn't possible with the P5Q-E unfortunately.

The Sharkoon volt mod cables do not work either! I bought a Zalman Fanmate 2 controller, and this works great. Put the fan down to 800 rpm and the system is complete silent now (while still running stable of course).
There is a new problem now: as I decoupled the blue power led, I need to check the keyboard numlock led to see if the system is on.

Thanks for all the help. And also thanks to this site for helping me building a true silent system!