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Do i use my sys_fan ports for my case fans

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March 25, 2010 3:51:28 AM

i have 2 sys_fan ports on my mobo. Can i plug my case fans into these ports? I have Ga-x58a-ud5 mobo. Also, what is the Pwr_fan port for?
a b B Homebuilt system
March 25, 2010 4:10:23 AM

Yep, you can use them for case fans. The perk of them is that you can control PWM fans, which most case fans are. The names on them are just for organization I believe, you can use them all for anything.
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March 25, 2010 4:29:19 AM

I searched a few forums and there are a few where people say u can. At others people say u should never do this and just use molex plugs directly to PSU. There are definitely different points of view on whether this is a good otr bad thing.
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a b B Homebuilt system
March 25, 2010 2:38:01 PM

The ports on a mobo marked SYS_FANx are intended for use with case fans. Within the BIOS Setup screens you will find that one or both of them offer to provide control of the fans' speeds, too. (Automatic control is enabled by default usually, but you can change.) The automatic control loops use a temperature sensor in the mobo and vary the voltage to the fans to alter the fans' speeds and achieve stable temperature at the setpoint. The alternatives offered usually include setting those fans' speeds to fixed values, or setting them to full speed at all times.

Many mobos today have 3- or 4-pin fan connectors, and fans come with either 3- or 4-pin connectors. They are designed so that both 3- and 4-pin fans can connect to any 4-pin mobo pinout and work properly. BUT a 4-pin fan MUST connect to a 4-pin output on a mobo.

3-pin fans work by varying the voltage supplied to the fan (red + VDC, black ground), and the yellow lead simply feeds a pulse speed signal generated by the fan back to the mobo for monitoring and displaying. 4-pin fans use a different speed control system called Pulse Width Modulation, and a different set of line color codes. The fourth line contains a "square wave" type of signal, except that its "% on" time is varied. Within the fan itself, that signal is used to control how much of the +12 VDC supply is fed to the motor for speed control. If you plug a 3-pin fan into a 4-pin output port, it will work because the PWM signal simply is not used by the fan. However, you may have to tell the BIOS Setup screen that you are using a 3-pin fan there so that it knows how to set up the +VDC line to achieve fan speed control.

There are two mobo fan ports that you generally should NOT use for case fans. FOR SURE you do not connect a case fan to the CPU_FAN port - that is for the CPU fan only. You may have a port labeled PWR_FAN, and it is intended for connecting a special lead set form the PSU so that the BIOS gets a speed signal from the internal PSU fan and can check it. But some have found that this port can power a normal case fan, probably with no ability to change its speed.
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a b B Homebuilt system
March 25, 2010 2:41:54 PM

PWR will power a case fan :)  I should have mentioned that but figured it was assumed, CPU_FAN is for your HSF fan, that's it, nothing else.
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March 26, 2010 3:38:38 AM

Thank you both for your help. Another thing..... i have fans connected to sys_fan1 and sys_fan2. I dont see sys_fan2 in my bios i only see sys fan1. I plugged front panel and back panel fan into mobo and i plugged top fan into molex (direct to PSU.) Any ideas?
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a b B Homebuilt system
March 26, 2010 1:10:33 PM

I looked at your mobo manual and it shows three SYS_FAN connectors in the diagrams on pages 7 and 25 - two above and below the lowest PCIe x8 slot at the bottom of the board, and one above the first pair of SATA ports near the mobo battery on the right edge. There's also a connector for a Northbridge chip cooler fan.

However, I am surprised to see in the manual no direct mention of how the BIOS is set for these fans. It says generally that system fan speeds and controls are in the section on PC Health Status. The only other reference is within the brief description on p. 78 of the EasyTune 6 utility. It has a HW Monitor tab where temperatures and fan speeds can be examined, but the manual does not indicate whether you can examine all three SYS_FAN systems separately. Moreover, it does not specifically state that these fan speeds are controlled by the BIOS; it only details some fan speed control information about the CPU_FAN. It appears that installation of the several Gigabyte applications like EasyTune 6 is mentioned on p. 68 of the manual.

The manual seems incomplete about how to do these things, and even about whether certain controls are available. But it may be that they are not done directly in BIOS Setup; you must install and use the EasyTune 6 application to do that.
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March 26, 2010 7:06:02 PM

Ive been reading manual for 2 days now and noticed the same thing. Its funny all my fans are running and in my bios i do see that one of them is connected (it shows a RPM reading) , but i dont see a rpm reading for the other one connected directly to mobo. Do u think it could be the type of fan? Im going to connect the top case fan to my mobo later instead of my front rear fan and see what happens.
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a b B Homebuilt system
March 27, 2010 1:09:25 PM

Type of fan should not affect this. Even on a 4-pin port with a 3-pin fan plugged int, ALL of the 3 lines are the same function. A 4-pin connector only make available the line for the PWM control wave signal on the 4th pin. Although the BIOS may need to be told which fan type it is trying to control (some figure it out themselves), the speed signal is no different so monitoring it should have nothing to do with fan type.

But judging from the manual, the BIOS only seems to have a place to examine / display ONE of the fans, even though the mobo has 3 SYS_FAN pinouts. As I said, the only hope I could see was the possibility that the EasyTune 6 utility might show you more, and maybe provide access to customizing.
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