Last week I received a broken Logitech 2.1 speakers set. The Logitech z-340 specificaly. The power light turned on but no sound and the volume knob produced a crackling sound when turning so the amp in the subwoofer is still working. I've tried disassembling the subwoofer but it's mostly glued together. So I first reverse engineered the speaker unit. It contains a small circuit board with the controls for the subwoofer. The left speaker and the subwoofer are connected with a 10 pin cable with din connectors. The speaker unit also contains a preamp for the headphones output

The reverse-engineered schematic

After some testing and probing on the circuit board I found out that the volume potentiometer is broken. I don't have spare stereo potentiometers lying around so I soldered two wires across it. Now the speakerset always run on full volume and I change the volume on my laptop.

After "fixing" the speakerset I found out that it sounds like complete crap. It has a very strong bass and a lot of treble but all the mid-tones are gone so I don't think I will be having this speakerset for long.