The volume knob in my wife’s Toyota Highlander behaved weirdly. As you turned it up or down, the volume setting would jump up or down, sometimes in the wrong direction and by an unpredictable amount. It didn’t give a linear output as you would expect.
What to do? Why, take it apart of course!
So first a bit of background.
The Land Before Time
In ye olden days everything was analog, as sinusoidal as ocean ripples. Volume knobs were merely variable resistors (or “potentiometers”) that were connected directly to the output from an amplifier of a stereo system. This would then directly attenuate — i.e., vary — the sound before it was sent to the speakers.
The Brave New World
In the future however, knobs have become digital, along with everything else. They don’t alter the sound directly though. Instead, they simply report their direction and perhaps speed to a microprocessor inside the amplifier so that it can make decisions about sound amplification.
One benefit with such a new-fangled knob is that there doesn’t need to be a hard limit on either end of its rotation. You can turn forever and you’ll never get to the end of the rainbow. Why is that?
Because again, a digital “pot” 1 only outputs direction of rotation, not “amount” of adjustment or position of its rotation. In other words, the volume is really just a software abstraction now. It’s a parameter that the amplifier determines by itself based on the user turning the knob one way or the other.
Another advantage of the digital pot is that now it can vary several qualities of the amplifier. No longer is it tied only to volume; now it can do sound fade and equalizer adjustments. Really, the possibilities are near infinite since it’s so heavily tied to software.
A big downside is that these babies can get dirty inside just as easily as an old fashioned analog pot. Even worse, they are way harder to clean than their ancestors.
Overall, I got really lucky on this project. Pulling a stereo — especially a factory model — can be a real bear. But as it turned out, the volume knob in question was connected to a little circuit board which then had a small ribbon cable which connected it back to the main amplifier board. I was able to remove this little subassembly rather easily and do all the hard solder work back at my bench.
The next hardest step was to remove the digital pot completely and clean its contacts thoroughly. Not easy with just a soldering iron, but not impossible.
Afterward, the knob works perfectly!
Below are some videos of others doing much the same cleaning process as I did.