Question Strange fault with 4-pin fan header on upgrade motherboard.

[PaulRB]

I just upgraded a very old motherboard (Foxconn A6VMX) in my 2U home server to a slightly less old motherboard (Gigabyte GA-78LMT-USB3). I just needed a couple more SATA ports, faster on-board LAN, USB 3, etc...

Everything has gone very smoothly, except one thing.

Both motherboards have only a single, 4-pin, chassis fan header. My case has 3x 50mm 4-pin fans. I used a 4-way adapter harness to connect the 3 fans to the Foxconn motherboard, enabling me to control the fan speed of all 3 fans, which worked well on the Foxconn.

The harness has the following connectors:

3x 4-pin sockets for fans, which have only 3 wires connected (power, ground & speed control/PWM) but the sense wire is not connected.
1x 4-pin socket, for the "master" fan, with all 4 wires connected.
1x molex socket for power.
1x 4-pin plug for the motherboard fan header. This has only 2 wires connected (speed control/PWM and speed sense. The power wires are not connected and not needed because the harness takes power from the molex socket).

This harness fails to work correctly with the Gigabyte motherboard. If I connect one of the 4-pin fans directly to the motherboard, the speed is controlled and measured as expected by the motherboard BIOS. But if I connect that same fan to the "master" socket of the harness and connect the 4-pin plug to the motherboard (and connect the molex for power) the fan runs at full speed all the time. The BIOS can measure the speed (~4000RPM) but not control it.

My immediate thought was that the speed sense wire inside the harness was broken. But I checked it with my multimeter and there is continuity (~0 Ohms).

Can anyone suggest any reason for this? Or anything else I could check?

Thanks in advance!

 

[Lutfij]

Welcome to the forums, newcomer!

My case has 3x 50mm 4-pin fans. I used a 4-way adapter harness to connect the 3 fans to the Foxconn motherboard, enabling me to control the fan speed of all 3 fans, which worked well on the Foxconn.
Instead of a splitter, why not use a PWM fan hub?

Make and models of the fans? A link to your fan splitter helps us two fold.

 

[PaulRB]

Welcome to the forums, newcomer!

My case has 3x 50mm 4-pin fans. I used a 4-way adapter harness to connect the 3 fans to the Foxconn motherboard, enabling me to control the fan speed of all 3 fans, which worked well on the Foxconn.
Instead of a splitter, why not use a PWM fan hub?

Make and models of the fans? A link to your fan splitter helps us two fold.

Thanks for responding. Yes, I should have included those details in original post, apologies for that, I should know better, being a long-term member of a different tech-related community help forum!

The fans are Silverstone FTF-5010. I do not recommend these fans, by the way, I have had 2 fail already and a third one going the same way. They start making unpleasant noises after a while. But there is a dearth of 50mm 4-pin fans on the market, it seems.

The splitter/adapter/harness .... I want to say Akasa, but I'm not certain, and I can't find it in my eBay or Amazon purchase history. I'll get back to you on that. But it worked fine with the Foxconn motherboard for at least 2~3 years.

 

[PaulRB]

Instead of a splitter, why not use a PWM fan hub?

Just noticed this question, sorry. Well, cost was probably one reason. Also I remember only seeing hubs with manual (potentiometer) controlled speed. I wanted something completely automatic. It seemed wasteful to use an "intelligent" hub when the motherboard already has that capability built-in.

 

[PaulRB]

link to your fan splitter helps us two fold.

Found it!

https://www.quietpc.com/gel-pwm-1-4-pwmcable

 

[PaulRB]

I purchased a fan hub and the problem is solved.

I purchased a Deepcool FH-04 4-way 4-pin fan hub. The motherboard is now able to read and control the speed of my fans.

https://www.deepcool.com/products/Accessories/accessories/2021/11375.shtml

Why this hub worked and my 4-way, 4-pin splitter cable/harness did not, I still don't understand. I doubt that the hub has any special circuit inside, I imagine it simply makes the same connections that the splitter cable does.

The only difference I can see is that the hub draws power for all the fans from the motherboard header, whereas the splitter cable draws the power from a molex connector. Why that difference prevents the motherboard from controlling the fan speeds, I have no idea. The splitter cable is not faulty, it worked fine on the previous motherboard, and I tested all connections with a multimeter.

Thanks @Lutfij for your suggestion. Do you have any theory as to why the hub works but the splitter cable doesn't?