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 Post subject: Which of these mobos has true PWM fan connectors?
PostPosted: Wed Jan 15, 2014 2:22 pm 
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Joined: Mon Jul 23, 2007 3:48 pm
Posts: 45
I'm trying to get a mATX Kaveri mobo which has 3 true PWM fan connectors (1 for CPU, 2 chassis).

So far I only see the Asus A88XM-PLUS/CSM and the Gigabyte GA-F2A88XM-D3H having 3x 4pin fan connectors, but I'm worried they might be 'fake' connectors.

Here's the layout diagrams from the manuals for each mobo. I'm pretty sure the Gigabyte only has one true PWM, but I'm not entirely sure about the Asus; not sure about what VCC is?

Gigabyte GA-F2A88XM-D3H
http://www.newegg.com/Product/Product.a ... gnorebbr=1
CPU_FAN
1. GND
2. +12V
3. Sense
4. Speed Control

SYS_FAN 1/2
1. GND
2. Speed Control
3. Sense
4. Reserve
------------------------------------
Asus A88XM-PLUS/CSM
http://www.newegg.com/Product/Product.a ... 6813132055
CPU_FAN
1. GND
2. CPU FAN PWR
3. CPU FAN IN
4. CPU FAN PWM

CHA_FAN 1/2
1. GND
2. CHA FAN PWR
3. CHA FAN IN
4. VCC


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 Post subject: Re: Which of these mobos has true PWM fan connectors?
PostPosted: Wed Jan 15, 2014 3:22 pm 
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Joined: Fri Aug 05, 2005 3:29 am
Posts: 1241
Location: UK
If it doesn't say PWM or indicate some form of control over fan speed then it is not PWM. So 'Reserve' or 'VCC' on the fourth pin = not PWM, but 'Speed Control' = PWM. And it is not just chassis fan headers that are at issue. Asus and other board manufacturers sometimes fit a four pin CPU_OPT PWM header but it can't be configured independently. That's because CPU_OPT simply mirrors the CPU PWM header settings, a form of on board PWM chaining. Some board makers have a four pin CPU2 header. But despite the four pins it is actually a three pin fan header, to provide support for three pin CPU cooler fans. Some CPU fan headers feature a mechanical detector switch and will change between four pin PWM and three pin fan operation based on the type of fan that is actually fitted. The problem with providing PWM chassis fan headers without this feature is that due to how PWM works any three pin fan plugged into them will run at full speed. For some users this is perfectly acceptable but it won't suit those for whom fan noise is an issue.

It is probably easier with PWM fans to run them as a chain off the CPU or CPU_OPT header using either the Y splitter cables provided by Noctua for example, or using one of the PSU powered PWM splitter cables.


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