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Trouble with PWM control on chassis fan headers w/ PWM splitter? - Page 6

post #51 of 53
Quote:
Originally Posted by MalsBrownCoat View Post

I don't mean to be "that guy" necro'ing a 2+year old thread, but I'm having what seems to be the same problem.
Toms Hardware forums = worthless.
ROG forums = worthless.

So far, this is the only *relevant* thread that I've been able to find. All of the others are about using 3 pin fans and expecting PWM control functions. DUH...

I'm *using* PWM fans, along with a PWM splitter, on a board that supports PWM on its headers (Crosshair V Formula Z) and still getting no control over my CHA FAN headers, regardless of which one I try.

TL:DR = was there any resolution/update on this issue?

Yes there is an update. Not all 4 pin fan headers offer PWM fan control on Asus motherboards.

This article here is for Z87, but the situation I presume would be similar for AMD motherboards:
http://www.silentpcreview.com/forums/viewtopic.php?f=28&t=66283

Quote:
Originally Posted by rhuebner, from SPCR Forums 
First off, watch out for the chassis fan headers, they're not what they seem. This board has 6 fan headers: CPU_FAN, CPU_OPT, and CHA_FAN 1-4. All of them look like normal 4-pin fan headers, but CHA_FAN 1-4 are *not* true 4-pin PWM fan headers. They don't provide any PWM control capability, and in fact act mostly like 3-pin fan headers, controlling all fans, whether 3 or 4 pin, using 3-pin style voltage control. The 4th pin, which should be used to control 4-pin fan speeds while the motor power stays at +12V, is instead hardwired for a constant 100% duty cycle PWM signal (fixed +5V). 4-pin fans will see this PWM signal and always run at full throttle, while the motor power is adjusted 3-pin style to control the actual speed resulting from that full throttle. 3-pin fans will work with these headers as if they were plain old normal 3-pin fan headers.

You can get a clue about this weirdness from the pinout diagrams for the fan headers in the user's manual. The 4th pin for the CPU_FAN and CPU_OPT headers is labeled as "CPU fan PWM", but for the CHA_FAN headers is instead labeled as "+5V". In the PWM fan control signalling scheme, a fixed, unmodulated +5V PWM line is just a hardwired constant full speed 100% duty cycle command. But I don't see the point of including it; PWM fans already default to constant full speed when plugged into standard 3-pin fan headers (leaving their 4th pin unconnected) anyway. This is just a tricksy way to make a 3-pin header look like a 4-pin header without really being one.

Why did ASUS go to the trouble of making fake 4-pin headers, when normal 3-pin headers would have worked just as well? It's not helpful, it just causes confusion. When someone plugs a 4-pin PWM fan into a standard-looking 4-pin fan header, they're going to naturally assume the fan will be controlled via PWM. If you plug a 4-pin fan into a 3-pin header, at least you know up front that you're sacrificing the fan's PWM ability and using it as a 3-pin fan. It's almost like ASUS is actively trying to conceal the fact that PWM fans aren't really supported and will instead be run in 3-pin mode.


It has only been starting from Z97 and on X99 that Asus has offered PWM and voltage control on all fan headers.


There does not appear to be a resolution to this issue. These 4 pin headers simply are not PWM fan headers. They don't offer fan control of any kind. You may be able to get some better control with SpeedFan, but otherwise you're out of luck - you'll need to buy a fan controller for the kind of fan control you want, as the motherboard simply does not offer it on the hardware level.
Edited by CrazyElf - 8/2/15 at 3:44pm
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Trooper Typhoon
(20 items)
 
  
CPUMotherboardGraphicsGraphics
5960X X99A Godlike MSI 1080 Ti Lightning MSI 1080 Ti Lightning 
RAMHard DriveHard DriveHard Drive
G.Skill Trident Z 32 Gb Samsung 850 Pro Samsung SM843T 960 GB Western Digital Caviar Black 2Tb 
Hard DriveOptical DriveCoolingCooling
Samsung SV843 960 GB LG WH14NS40 Cryorig R1 Ultimate 9x Gentle Typhoon 1850 rpm on case 
OSMonitorKeyboardPower
Windows 7 Pro x64 LG 27UD68 Ducky Legend with Vortex PBT Doubleshot Backlit... EVGA 1300W G2 
CaseMouseAudioOther
Cooler Master Storm Trooper Logitech G502 Proteus Asus Xonar Essence STX Lamptron Fanatic Fan Controller  
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post #52 of 53
Something does not make sense.
If pin-4 (PWM control) is not used the PWM fan will run at full speed. This is a fact. So how can the fan run at full speed if pin-4 is at a constant 5.5v?
post #53 of 53
I stumbled upon this thread while trying to figure out why my recently purchased Arctic Cooling PWM fans would only run at full speed.

I have an M5A97 R2.0 motherboard and have found even more weirdness with the fan control. My Chassis Fan 1 and 2 ports will not control fans with either PWM or the voltage signals (3 or 4-pin), but the Chassis Fan 3 port will vary speed with either 3 or 4-pin fans. I think it's controlling them based off voltage since it works with PWM and non-PWM connectors. It's not exactly what I wanted to have to do, but I have my 4-pin PWM fans connected to the CPU Fan connector with splitters and my 3-pin fans are connected by splitters to Chassis Fan 3. All fans do now change speed over the ranges I wanted them to. Hopefully this helps somebody else with these problems.
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