I also designed a fan duct for it: http://www.thingiverse.com/thing:1634657

I would be inclined to solder small jumper wires to the board that then lead to the through-hole components.  That helps relieve the strain on the traces.

It seems a lot of the confusion around this mod is that the DaVinci main board is actually capable of switching four fans. There's the one used from the factory, the one I filled in, and another two on that Fan2 header to the left that I assume is used on the Duo. It's more obvious when seen from directly above, but a picture from above doesn't really show the components I added.

Did you end up using SMD components?

The long answer is at https://github.com/luc-github/Repetier- … issues/165 - there are some firmware modifications involved. It's also worth checking your board to see if you already have the resistor and transistor that I had to add - apparently there was a previous bug where someone already had them from the factory on a 1.0A.

And yes, reflashing the firmware preserved my printing timer. I exported the EEPROM to XML via Repetier-Host, though, and you can also just restore it afterwards.

I'm still waiting on an order of fans, so I'll have to wait to see how the whole setup functions.

Now to see if it works.

And it apparently didn't occur to them that this breaks the component search engine on their website.

By the datasheets, this has to be a PMBT2222A. Even if I had completely misunderstood the circuit and a PNP was correct, the BFT92 has a tenth of the necessary current.

The good news is that a PMBT2222A has a max rated current of 600mA, which is just fine for running the E3D v6 fan. It's also enough for the set of four 60mm fans I plan to put on the sides of the case and try to use for layer cooling without mounting a fan on the carriage. The only question at this point is whether I stick to SMD or try to put through-hole components on the SMD pads. Not sure about that yet.

Here is a thread on github that offers limited info about the mod itself, and good info about changing the FW to support it:

https://github.com/luc-github/Repetier- … /issues/64

As you work this out, please document it well.  I've seen very little useful info on doing this.

I'm also a bit confused about the transistor. If I trace the wire for the working extruder fan, it leads to a SOT23 package labeled "W1P 52" which seems to correspond to a BFT92 PNP transistor, but a PNP transistor doesn't make any sense at that place in the circuit. I keep looking for a way I'm reading the label wrong or somesuch, but I can't seem to figure out where I'm getting it wrong.

We know that the current limiting resistor going to the base of the NPN transistor from the micro controller is rated with enough ohms to open the "gate" of the transistor enough so sink the 5V that the original fan runs off of,  but potentially not enough to sink 12 V.   

That having been said, ground is ground, and the only thing you would risk is the E3D fan not running as fast as it usually would.

I like your idea, but I think I would rather use it to control a 12V layer fan, and just keep the E3D fan on permanently.

This means that if the ground is the same across the 12v and 5v rails and the current through the 12v fan isn't too much for the NPN transistor, you can just wire your fan from the 12v supply line everyone is tapping to the same switched ground the original fan used. A quick check with a voltmeter showed that the ground lined up and fan currents are pretty low anyway, so I went ahead and tried it. It worked. I wouldn't recommend this as anything permanent until I get a chance to check the parts on the mainboard to make sure the currents are okay in the long run, but it's promising.

Has anyone else poked at this before? Has anyone here tracked down where this NPN transistor lives on the mainboard (and more importantly, where the second NPN transistor that's only populated on the Duos lives?)