How I Fixed One Of The Most Annoying Problems With Old Car Stereos

The technology found in car stereos (ahem, entertainment systems) has changed a great deal over the decades. The humble AM-only radio was supplanted by AM/FM units. 8-track cartridges had their moment, only to be replaced by compact cassettes, which were in turn rendered obsolete by CDs. And the same fate befell CDs as digital music technology allowed for MP3 players, USB drives, and Bluetooth audio. Now, the modern car stereo is as much an Internet portal as it is a radio.

Still, throughout all those changes, car stereos have retained some familiar features. Chief among them might be the volume knob (touchscreen abominations notwithstanding). The knob as a thing we twist to control volume is so fundamental to the way we interact with a stereo that the very act of changing the volume is referred to with knob-turning lingo, like ‘crank’ it up or ‘turn’ it down.

But the modern volume knob is not a living fossil. It may look and behave in many ways like its muck-dwelling ancestors, but like most everything else in our cars, it has been changed in some very fundamental ways by the evolution of technology.

A blemish on an otherwise perfect car

My daily driver is a 2010 Honda Fit. I love my little Honda. It’s reliable. It gets excellent mileage. It can hold a ton of stuff in the back. And I found one with a stick shift!

What I don’t love about it is its balky volume knob.

A few years ago, I noticed that the stereo’s volume was not changing as smoothly as it used to. Since then, the problem has only gotten worse. Now, instead of the volume smoothly changing as I turn the knob up or down, it jumps around wildly. Rather than going from zero to fourteen in even steps, it might go from eight to zero to four to fifteen.

And this isn’t just a problem with my car. My dad’s 2012 Honda Civic has the same affliction, and according to Internet forums, so do many other Hondas of that era.

I’ve been meaning to dig the stereo out of my dashboard and try fixing it for a while now, but I just haven’t gotten around to it. Recently, a friend of mine bought a Honda Fit for himself, and wouldn’t you know it, it’s stereo had the same problem. But unlike me, he actually decided to do something about it.

One day, a couple of weeks ago, he texted me some photos of his disassembled car stereo and asked me what he should do to fix the volume knob. I tried explaining things over the phone, but eventually I told him he could just bring it to my house and we would work on it together.

Techno Jargon blah blah

Before getting into how we repaired his stereo, we should talk about the way the volume knob works on a modern stereo. And before we get into that, we should talk about how the volume knob works on an older stereo.

For most of the history of stereos, the volume knob was attached to an electronic component called a potentiometer, a type of variable resistor. In most of these devices, the potentiometer would have been used as a voltage divider, a bit of circuitry that splits a voltage and sends it through two different parts of a circuit. It’s a little bit like the proportioning valve in a car’s braking system, but for electricity.

The potentiometer, when acting as a voltage divider, directs a portion of the audio signal to an amplifier to be, well, amplified, and played through the speakers. The other part of the audio signal is sent off to the ground where it does nothing. By turning the potentiometer, you adjust how much of the audio signal is sent to the amplifier and how much is sent to the ground. The more you send to the amplifier, the louder the sound comes out of your speakers. The less you send to the amplifier, the quieter the sound is.

More modern stereos tend to replace the potentiometer with a different device called a rotary encoder. Rotary encoders come in dozens of types, with some very rather elaborate in design, but no matter what kind of technology they are using for their operation, they are essentially just a sort of switch that you spin. As the encoder rotates, it opens and closes an electrical contact, creating digital pulses. The computer (or other circuitry) attached to the encoder watches those pulses and translates them into some other action, like changing the volume or tuning to another station.

The ability of rotary encoders to control multiple functions of a stereo has made them a popular choice for designers of car stereos, especially as the necessary computing hardware has gotten cheaper. Another plus is that they are supposed to basically never wear out. But as we all know, reality often has a way of defying our intentions.

Fixing my friend’s car

I knew the problem with my friend’s car was going to be the rotary encoder. Having lived with this problem on my car for years, I had plenty of time to think about what could be wrong with it. Some rotary encoders do their switching with actual mechanical contacts. Others use magnetic sensors. And some use beams of light that are repeatedly interrupted as the encoder turns. My theory was that my stereo had an optical encoder and lint had somehow gotten inside of it, and the lint was partially blocking one of its light sensors.

From the photos my friend sent me of his disassembled stereo, I deduced that the rotary encoder was a hollow-shaft model made by Alps Alpine.

That ended up not being much help because the datasheet told me nothing about what was inside the encoder. To see what was wrong with it, we were going to have to disassemble it, which first meant desoldering it from the circuit board it was attached to.

Removal ended up being a whole ordeal because the encoder was attached to the board by three electrical connections and six beefy legs that were very well soldered. Through the careful application of lots of heat and curse words, I eventually got it off.

By carefully bending back a few metal tabs, I was able to open the encoder up and take a peek inside. I saw then that my theory had been wrong. It was not a light-based rotary encoder and there was no lint trapped in it. It was a mechanical encoder with little metal wipers that slide over a circular track, making and breaking electrical contact as they go. It was also full of filthy grease.

I wiped the grease out with a Q-tip, but everything else about the encoder looked fine. The wipers weren’t bent and the track they slid over wasn’t damaged or corroded. For good measure, I carefully buffed the tips of the wipers with a pencil eraser, and tweaked them a little so they would press onto the track with just a bit more force. The only thing left to do was reassemble the encoder, solder it back onto its circuit board, and put the stereo back together.

We did all that and … the volume knob worked like it was supposed to again. I don’t know if it was because we removed the dirty grease or because I refreshed the wipers, or both, but the knob was fixed.

Before we worked on my friend’s stereo, I had poked around in various forums to see if anyone else had attempted a similar repair. There were a number of people describing the same problem and asking if it could be fixed, but forum dwellers being who they are, were replying with helpful advice like, “Your stereo can’t be fixed. Go buy a new one.”

I’m glad to say that’s not true, and now that I know the repair isn’t that difficult, I will be doing it to my car as well. I may even help my dad fix his. And, if you own a Honda with this problem I hope you’ll feel empowered to try fixing yours, too.