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.
I found it frustrating as a young engineer 50 years ago how fixing things was already out of style. My first job introduced me to the “FRU” or field replaceable unit. Take out the old one, put in a new one. Design criteria for the FRU is lowest manufacturing cost, no consideration of repairability and serviceability. Its only gotten worse since then. These radios could be designed to service the volume control without major surgery but aren’t. Current designs only cost less to fix than replace if labor is free and replacement parts can be located.
I have a 2009 Honda Civic Si, and though it doesn’t have issues with the radio volume knob, it has a much more annoying issue of phantom changes of the mode. On top of it, the steering wheel controls do different functions than labeled, pike volume changes chanel and chanel changes mode. It’s quite annoying and sometimes results in rapid firing switching between modes every few seconds.
For the supposed reliability of Honda products, I’ve found it to be the least reliable car electronically I’ve ever owned. And I primarily own vintage BMWs and Jeeps as well as an old British roadster. I have a coworker with the same model Si and it has more or less the same electrical issues.
A big reason for why they went to the rotary encoders was also so you could adjust the volume from the steering wheel button, which wasn’t really possible with a standard potentiometer (unless you motorized the potentiometer to move when the steering wheel button was pressed).
BMW’s from the early 2000’s have similar problems, usually due to physical damage from the volume knob mounting location being made out of cheap plastic (and because the volume knob is the power button so it gets pressed on a bunch). I’ve taken apart quite a few and glued everything back together and reinforced with screws, that usually does the trick.
What a great mini-deep-dive into volume knob technology. This is how I like to start my day. Thanks!
Reminds me of how we used to clean the innards of a mechanical mouse. Which used, you guessed it! Rotary encoders. Although the most often cleaning need came from cleaning the surface of the the plastic bits that spun in two different planes as they seemed to like to get covered in various goos and detritus picked up by the mouse ball as it traversed across the crusty old mousepad crumbling away on your desk.
I will never for the life of me understand how a mouse pointer works.
My first job after I graduated was fixing machinery in a factory. Unless something obvious is broken the first attempt is always: strip it, clean it, put it back together. It works most of the time.
This piques my interest, because my spouse drives a Fit with that very head unit. Thanks for a great “how I fixed it” article!
Welcome! I hope this ends up being helpful
My 30 year-old alarm clock has had this problem for a long time. Volume is fine a tenth of a millimeter up from zero, then it jumps to deafening. I’ve known it was a dirty pot for a long time, but I just have never had the gumption to get in there and fix it. I was hoping it was easier than this, but maybe it is on an alarm clock…
That might just be a potentiometer? I dunno, 30 years seems pretty old to have a rotary encoder for a volume knob in an alarm clock, but who knows!
Holy cow. That knob should be able to be pulled/pried off for maintenance. It’s a pretty simple way to solve the problem, but OEs are gonna OE.
This happened to our Honda after just 2 years — it would “runaway” to really high volume (something you don’t mentally prepare for) and you’d have to kill the HU in a second or two once you saw it happening. The shop tech guys admitted they ended up searching the Honda-Tech forums for a solution and it was, in fact, dust that needed to be blown out. I don’t think they had to disassemble it to this degree, and I’m glad it was a warranty item (one of only 2 or 3 we ever had)
Having the knob designed to be removable is unfortunately the more expensive option for OEMs in multiple ways. Additional warranty claims from people breaking things ‘that are designed to be cleaned’, beefing up the design to handle non-idiotic user cleaning methods, and more common failure due to the more ‘complex’ design. I’d be very surprised if Honda had to warranty more than a thousand head units for volume related failures on any given model year vehicle.