The little speed controlled fan inside of my cable box (or more likely a temp sensor) decided to fizzle a few weeks ago. Everything else seems to be fine, but the fan speed goes from “jet-engine” to “whisper” and back randomly and for no reason. Some may call me fickle, but you try watching TV or sleeping in a room with this monster!
DIY Fan Speed Bypass Fix
Disassembly was a cinch, aside from the nasty “System Zero” security screws (Yes, the same ones Nintendo used on the SNES!) To remove use the correct driver, slot them with a dremel, or (carefully) use pliers. I replaced mine with some nice phillips-head machine screws I had lying around.
NOTE TO MANUFACTURERS: Security screws are ridiculous. With tools for all of them available to everyone it’s like putting a lock on something that you can buy a key for at Wal-Mart. Not to mention, unscrewing a screw on something I own, in my home, doesn’t violate any laws anywhere. Warranty, debatable; laws, nope.
I digress. Now, aside from the fan, everything is working perfectly with this box. I debated trying to determine the root cause of the fan issues, but I’m to lazy to do the research necessary, learn new skills, etc. In the end I decided there has to be a way to simply force the fan to one “moderately quiet” speed. If i get a few more years out of this DCT i’ll be happy!
The DCT has all of the working components of your standard PC and, as I suspected, the fan is a variable speed 12V brushless DC type just like you’d find in a laptop, or your PS3. Could be the controller built into the fan, could be a temp sensor, who knows. I know that if you avoid hooking up the third wire (yellow, sometimes blue) on the fan, it will run at fill speed. I tested this to make sure it ran at full speed without hiccups and it was good.
Next step, speed. I could have worked out how to ge the fan’s speed controller to force it to run at a set speed, instead I went the simple/lazy way again. I grabbed a 1KΩ pot I had in the junk pile and twisted it until the fan made no noise but was still moving a fair amount of air through the box. The meter said the pot was set to about 89Ω.
I had no 89Ω resistors so i just tied 3 320Ω resistors together. Close enough. A little solder and some fancy shrink tubing and I can finally watch TV a little more peacefully. I didn’t actually calculate this, but I estimate the efficiency lost by using resistors in this circuit will cost me around $0.00000001/day in electricity. Totally worth it.