I get emails from readers every now and then — but no topic has caused more interest than the 6-pin fan header on my two Inter-Tech server cases, 4U-4416 and 4U-4129-N.

Perhaps for good reason, it allows for the internal 120 mm fans to be PWM controlled. But is completely undocumented! Let’s have a closer look 😃

Table of contents
Intermit.Tech has made a video about a similar fan header on the Inter-Tech 2U-20255 case: https://youtu.be/n_9mLI4Oprw?t=150

Our 6-pin header

The header is located right next to the molex power connector for the 3×120 mm internal fans.

Fan molex and pin header, photo by Julien Brunet

A reader, Julien Brunet, tested where the pins went and made a pin-out table.

Fan Pin row 1 Pin row 2
Furthest PWM Tach
Center PWM Tach
Closest PWM Tach

The 4-pin fan header

A standard 4-pin fan header provides the fan with 12V, GND, sense and control.

Pin Wire color Function
1 Black GND (0V)
2 Yellow +12V
3 Green Sense/Tach
4 Blue Control/PWM
In our case the 12V and GND are supplied by the molex power connector, and the sense (Tach) and control (PWM) is available through the 6-pin header.

Using the 6-pin header

There are two ways that we can use this header to control the internal fans: individually and together.

To utilize the PWM signal — you will need fans with 4-pins.

Individual fans

Schematics for fans wired individually

We can connect the PWM and Tach signals for each fan to a 4-pin fan header on the motherboard, or some other fan controller. This will require three fan headers, and allow us to control and read the speed of each fan individually.

Unraid dashboard with fan speeds

Inter-Tech has apparently made a cable for connecting an 8-pin header to four 4-pin fan headers, supporting four internal fans. It is part of their 120 mm fan set — and this is what it looks like:

Inter-Tech fan cable, photo by Julien Brunet

But some jump (DuPont) wires can easily be used instead, just make sure to double check the pin-outs first.

Fans wired together

Schematics for fans wired together

Another way to control the fans, which will only require a single 4-pin fan header, is to connect the PWM signals together.

Note that we should not connect the Tach signals together.

Let’s have a look at a Noctua NA-SYC1 fan splitter — it takes a single 4-pin fan header and turns it into two. Similar to what we are trying to do.

Noctua NA-SYC1, from the user manual

Looking closely at the Noctua Y-cable, we can see that it splits the PWM signal, but not the Tach signal.

Noctua NA-SYC1 4-pin fan splitter (Y-cable)

This makes sense, as the PWM is a controlling signal going from the motherboard to the fans. But the Tach is the RPM readout going back — so combining the Tach pins makes no sense.

I suspect you need the Tach signal from a single fan to satisfy the motherboard, or whatever fan controller you are using.

Here we can clearly see that one connector is missing pin 3 — the Tach signal.

Noctua NA-SYC1 4-pin fan splitter (Y-cable)

Postface

A special thanks to Julien Brunet for helping me figure this connector out 👍

So with this I feel I have done my part in documenting what this header actually does. I hope you found it useful 😃