My 4-year-old iPod mini died yesterday in a tragic incident involving a moth and a cupful of coffee. It survived a couple of traumatic crashes on the floor, and two surgical procedures: I opened it once for replacing the battery, and again to fix a loose headphone connector.

This last problem was difficult (i.e., fun) to diagnose. One day I realized that all the songs on my iPod had become instrumental pieces: I couldn’t hear the singers voice anymore! A little experimentation suggested that, somehow, a certain band of frequencies were absent from the output: the same band that contains the human voice singing range (say 440-1000 Hz). For some songs, like Still Alive the effect was particularly clean as the spectrogram of voice and harmony is clearly separated.

Now this looked like a typical software problem: somehow the equalizer’s settings had been messed up. I tried resetting the firmware, but the problem persisted. So I resolved to open it. From what I could guess, the mp3 decoder in the iPod is constituted by several different ones, and each of them takes care of a certain range of frequencies. These decoders output their signal to a common digital-to-analog converter, from which the headphones line starts. The decoders and the DAC are not on the same chip, rather the DAC is a separate component just behind the headphones jack. Part of the wires were loose, and so part of the frequencies couldn’t be heard.

              _______
|f1|-------> |       |
|f2|-------> |       |
|f3|-------> |  DAC  | ----> headphones 
|f4|--x----> |       |
|f5|--x----> |       |
      |       -------
       
         loose wires

So the diagnosis was that the wires got loose when I last dropped the iPod on the asphalt while I was running, and the fix was to insert a little piece of plastic in the connector.

I’m shopping around for a new iPod, and in four years there has been a lot of improvement in the form factor and the aesthetics. Unfortunately, the more compact they get, the less “user serviceable” they are, meaning that if it doesn’t work, you just throw it away, without any chance of fixing it yourself.