Question Has anyone ever soldered an additional fan header?

Jul 13, 2022
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I'm re-homing an HP Elitedesk 800 G1 sff into a new case, but it only has one CPU fan header and no chassis fan headers. However, under closer inspection there is one spot for a chassis fan header on the motherboard, but it doesn't actually have the header installed, just bare pads.

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So I was thinking I could just get a spare 4 pin female header and solder it in there. I've tested with a multimeter, and the square pin seems to be ground, then 12 V, and I think the last two pins are floating (TACH and PWM) (if this is a standard connector).

Has anyone ever done something like this before?

One thing which worries me is the surrounding circuitry with lacking components (this could explain why the last 2 pins are floating). It looks like there should be some SMD 2 and 3 pin components, as well as an electrolytic capacitor. The cap has continuity with the first 2 pins of the header, aka GND and +12V, so I think it could be used as a filter...? The other components I'm not sure.

PS I know that I can just hook a fan to the power supply or get a hub, I'm just curious if this could work.

Thanks for your help!
 
Jul 13, 2022
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Turns out, there is a schematic for a motherboard from the same manufacturer only 2 generations newer. According to that, the supporting circuitry is pretty important for the PWM + TACH signals. It has all the component names, so theoretically it should be possible to add this fan header...
 

Zerk2012

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Turns out, there is a schematic for a motherboard from the same manufacturer only 2 generations newer. According to that, the supporting circuitry is pretty important for the PWM + TACH signals. It has all the component names, so theoretically it should be possible to add this fan header...
2 generations newer so nothing to do with your exact board!

You can do as you wish at your own risk! It's your PC.

Buy a fan splitter cable and use the CPU fan header, buy a fan controller, buy a Molex to fan adapter!
 
Jul 13, 2022
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2 generations newer so nothing to do with your exact board!
The component numbers are exactly the same as on my current board. I can imagine the manufacturer left this part of the PCB the same, since I don't believe fan header circuits differ very much generation to generation. It could just be a coincidence, though...
 

Zerk2012

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The component numbers are exactly the same as on my current board. I can imagine the manufacturer left this part of the PCB the same, since I don't believe fan header circuits differ very much generation to generation. It could just be a coincidence, though...
You act like your mind is already made up instead of looking for easy work arounds so go for it.
 
Haha pretty much :) I guess I'm just looking for any advice from people who are more experience in this kind of thing
It's probably not that often someone would do this since it's way easier to add fans using a fan control hub. They're fairly cheap...and small enough to fit between the back cover and motherboard tray. There are models that can take input from the CPU header to control speed of a whole array of chassis fans along with the CPU fan.

This is just speculation since I've never done this and don't know how your motherboard is set up. But you'll have to find the right components and solder them on the board as well as the header connector. But even after that you'll probably not have BIOS support to control the fan through the header since it was not built anticipating it would do so. It may not even initialize the fan controller so it would never turn on. Or if it does it may just run at full speed constantly...same as a fan connected directly to the PSU would.
 
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Jul 13, 2022
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It's probably not that often someone would do this since it's way easier to add fans using a fan control hub. They're fairly cheap...and small enough to fit between the back cover and motherboard tray. There are models that can take input from the CPU header to control speed of a whole array of chassis fans along with the CPU fan.

This is just speculation since I've never done this and don't know how your motherboard is set up. But you'll have to find the right components and solder them on the board as well as the header connector. But even after that you'll probably not have BIOS support to control the fan through the header since it was not built anticipating it would do so. It may not even initialize the fan controller so it would never turn on. Or if it does it may just run at full speed constantly...same as a fan connected directly to the PSU would.
Ah, I forgot about the BIOS. I'll snoop around and see if it supports a second fan. The tower versions of this computer support a chassis fan, so maybe I can put that BIOS onto this motherboard...?

On second thought, I think I'll stick with a hub / PSU
 
...The tower versions of this computer support a chassis fan, so maybe I can put that BIOS onto this motherboard...
That's a whole other sticky wicket. First rule there is have a method to recover to a known-good BIOS if the BIOS hack fails to work. That frequently means something like a re-moveable BIOS e-PROM chip that allows you to update it on an e-PROM programmer and plug back into the board.

And such a Frankenstein BIOS update rarely works out since various hardwares (such as audio and LAN) are frequently different and don't initialize properly.
 
Jul 13, 2022
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That's a whole other sticky wicket. First rule there is have a method to recover to a known-good BIOS if the BIOS hack fails to work. That frequently means something like a re-moveable BIOS e-PROM chip that allows you to update it on an e-PROM programmer and plug back into the board.

And such a Frankenstein BIOS update rarely works out since various hardwares (such as audio and LAN) are frequently different and don't initialize properly.
Ok, thanks for your advice!
 

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