FAN MOD FOR ADSL MODEM

Well after having some problems with my Dlink DSL 300+ modem, with it freezing up on me and generally being a pain in the butt, i decided to take it upon myself to work out why. So i pulled it apart, and nearly burnt myself on the 2 chips inside. According to the specs, the main cpu runs at 25 mhz, and runs pretty toasty. Which i found out pretty damned quickly. Just putting a heatsink on the chips wont do much, cos there isnt enough room for a Fan HS, and a passive HS still needs air flow and in the little box it didnt get much air flow at all.

So the totally natural conclusion to this is to put a fan in!!!!

Ok heres some pics, the modem itself.

Open the clamshell case, and you get this...

Here is the Helium 210 CPU. It has 4 meg of ram from the nanya DRAM chip
just above it. This chip gets really hot.

And here is the ITeX ADSL controller. It gets pretty damned hot as well. Hot chips
cause the modem to act stupid. Time for some cooling action.

I had several plans, but i was limited by the size of the modem and the smallest fan i could get hold of. I ended up using some old fan of some video card. I think it might have been a geforce 2 pro fan. It was a bit busted up and the bearings were dry, so i oiled them up and sealed it of.

Before i decided to cut anything and regret it, i decided to make sure i could get power for the fan first. Now the ADSL modem uses a 7.5 volt plug pack. It was a 5 volt fan, so that was out of the question. There is an on board PSU for the chips, but it only put out 3.3 volts which didnt even start the fan up. There would have been a 5 volt supply as well, but i didnt find it, and i didnt want to use it, because it would be for powering the ethernet interface driver, and i didnt want to screw that up by stealing power for a fan.

The only option i had left was to use the 7.5 volts DC and drop it somewhat for the fan. I used a 100 ohm resistor and soldered that into the board. When i hooked the fan up to it, it spun up nicely and sat at 4.75 volts. This kept the fan nice and quiet, and didnt drag power from anything. Here is a pic. I soldered the resistor into the board on the 7.5 volt line and the black wire onto an earth. It let the fan run perfectly.

Done. Now the internal board has a lot of capacitors sticking up, and i had to make sure that i cleared those components, as well as getting air over the 2 hot chips. Lucky this fan was pretty thin, and due to the way i mounted it in the case lid, it had plenty of clearence.

So the plan was simple. To cut a hole in the case lid, and provide power for the fan. Now i dont have any hole saws of any kind, so i had to cut a hole in a bit more of a dodgy way. First, i marked out the size of the fan. Much to my joy the fan diameter is the same as an old toilet roll cardboard tube. So thus armed with pen and cardboard tube, i marked the hole.

Right, now to cut the hole. I have cut holes before using a drill, and then using a small saw blade, to join the holes, and then file it out into a circle. This time i tried something different. I used a soldering iron :D
The iron had a small thin tip, so using that i cut out a circle of plastic smaller then the hole i marked. Do this in a well ventilated area, cos plastic fumes are BAD.

I then got my file and pocket knife out. Using a half moon file (where one side of the file is curved in a ")" shape) i filed the circle out to the red line. The pocket knife i used in a carving motion to smooth the edges out. You have to be very carefull, and use a knife with a THICK blade. It wont really well with a thin blade knife. Be careful, you can slice your fingers off if you slip. Just use the knife to carve and smooth out the edges.

With the hole nice and circular ( i thought i did a pretty good job) it was time to put the fan in. In my case, the fan had two little plastic supports out from the hub. I used those supports and some friendly super glue to attatch the fan to the case. Like this...

Here is that in a bit of detail, i used the super glue to attatch the fan, shown by the blue circles.

I then soldered longer wires and super glued them to the case for some strength.

So its done. Whats does it look like?

How loud is it? As loud as a typical video card cooler of 3 years vintage. In other words, barely audible. And the modem hasnt crashed once.

And it has that sorta hi performance jet engine look-a-like thing happening.

Todays experiment....

Success!!!

Scuse the Excel Saga reference... :D

Cheers, Rain.

13 July 2003