in Featured, Hardware

Saved from a $400 radio replacement with a $9 tube of solder paste and some risk-taking

One day in 2018 the stock head unit in my Dodge Challenger suddenly stopped playing AM and FM radio stations. The radio was as basic as a radio can be. No touch screen. No color other than green text on a black background. A Mopar RES 130S, to be precise.

For years I was barely bothered by this inconvenience because the CD player, AUX input, Bluetooth input, and hands-free calling features all continued to work just fine. Heck—even the SiriusXM preview channel played—just not well enough to entice me to purchase a subscription beyond the original one-year trial I was granted back in August 2011.

Then one day in 2022 everything changed. No CD. No AUX input. Nothing. The radio powered on and I could change input sources, but I couldn’t hear any sound from the speakers except for a faint click spaced every ten seconds.

Cue the #FirstWorldProblem hash tag, because I was now in crisis mode. Driving without music? Inconceivable!

It seems I wasn’t alone. Internet forums going back a half-dozen years shared that this is a common issue with this model radio used across several different Chrysler vehicles over the years. But the radio model is discontinued, and used ones sell on eBay for $400. My options were:

  • Install an aftermarket radio, losing convenience of steering-wheel mounted radio controls
  • Take my chances and buy a non-returnable used model at $400
  • Trust the forums and attempt to re-solder the culprit: a tiny integrated circuit (IC) chip

Recently, I’ve experimented with soldering through-mounted components as there’s an intersection between the amateur radio hobby and the art of soldering. Although soldering was a requisite skill set to enjoy amateur radio in years past, it’s not necessarily a requirement today, especially with the miniaturization of electronic circuitry in modern history. Components today for mass-production electronics (vs. hobbyist assembly) are so small that they’re mounted to circuit boards by precision robotics—not chubby, shaky human hands like mine. Further, I didn’t even have the knowledge or skill set to troubleshoot and confirm this particular chip was indeed the problem. But what did I have to lose? The radio was already completely broken.

I owned a soldering and hot-air rework station for my amateur radio hobby. All I needed was a $9 tube of solder paste. I learned solder paste behaves a bit different than a stick of solder in that it’s intended to be heated by hot air instead of the tip of a traditional soldering iron.

The photos below show my progress as taken through the zoom lens of the camera on my mobile phone. That large chip in the center of Figure 1 was my target. In reality, the chip was about the size of the fingernail on my pinky finger, and it has about ten or fifteen even tinier metal legs protruding from all four sides. Go ahead and try to count them if you’d like.

Here we go:

Figure 1: According to folks on the internet, the integrated circuit (largest chip shown) is known as a “radio-on-a-chip” and is the culprit behind audio tuning and volume control issues I experienced.
Figure 2: Solder paste is sold in a syringe with a plastic tip. The small gray line in the upper-right near the blue plastic tip is where I practiced getting a feel for how fast or slow the solder paste flowed from the syringe.
Figure 3: That’s about as neat as I was able to spread the smallest amount of solder paste while ensuring I appropriately covered each leg of the chip on all four sides.
Figure 4: Solder paste liquefies and turns shiny when heated with a heat gun. Unfortunately, it left behind some bridging across several legs of the chip which represents a short circuit. What isn’t pictured is that I removed the solder bridges by slowing dragging a small-tipped soldering iron across all the legs after adding some additional flux. I learned that tip from a YouTube video.
Figure 5: With all solder bridges removed, I then washed away the residual flux with isopropyl alcohol applied using a cotton swab.

After the soldering was complete I re-assembled the radio and reinserted it back into my car. Although there were other challenges with a broken plastic FAKRA (Fachkreis Automobile or Working Group Automobile) antenna connector—an entirely separate topic for another day—I surprised even myself that all radio functionality worked again like on day one and continues to work several weeks after taking a risk and trying something new.