---
title: "Make Your Ears Bern"
date: 2018-01-11
lastmod: 2019-01-16
categories: ["Blog"]
tags: ["electronics"]
---
A colleague offered a pair of Bern Bluetooth drop-in headphones to me fore free,
with the catch being: _I had to fix them_

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# Don't Turn It On, Take It Apart!
Past mistakes have taught me to be gentle and patient when it comes to taking
things apart. This was no exception either. After looking over the unit on each
side, I figured the only way *in* was lifting the mesh cover off. So I went at
it, carefully, with a pair of tweezers. I worked my way around the edge and
wedged the mesh upwards.

{{% admonition info %}}
![Zoom, Zoom, Zoom!](/img/headphone-fix/IMG_7505.jpg)
{{% /admonition %}}


# Okay, Maybe Turn It On
Now that the problematic speaker side was successfully opened without any
damage, it was time to investigate what was wrong.

I played a song via smartphone on the speakers. The result was as expected: _the
right speaker put out no sound._ I checked the known-good left speaker using my
**Rigol 1074Z** oscilloscope. This may not have been entirely necessary, but I
wanted to find out what to expect when troubleshooting the right channel.

{{% admonition info "Left Speaker" %}}
![Left Speaker](/img/headphone-fix/IMG_7506.jpg)
{{% /admonition %}}

{{% admonition info "Right Speaker" %}}
![Right Speaker](/img/headphone-fix/IMG_7511.jpg)
{{% /admonition %}}

Knowing what to expect on the oscilloscope, I hooked up the probe to the right,
problematic, speaker. The result was much different, indicating either noise or
an open circuit. It may be worth mentioning that the right speaker was
disconnected at this point in time to ease the troubleshooting process.


# Where Did It All Go Wrong?
Lucky for me the PCB pads were labeled -- even better `SPKL+` (_left_) and
`SPKR+` (_right_) were easy to find.

{{% admonition info %}}
![Under the Microscope](/img/headphone-fix/IMG_7507.jpg)
{{% /admonition %}}

Outside of the bluetooth board hidden under the piece of tape, there's not a
whole lot going on in the circuit. It was my guess that the visible surface
mount QFN chip was most likely the op-amp used for the speakers. A quick Google
search of `AIWI TI` (_as shown in the photograph_) resulted
in [the following datasheet](http://www.ti.com/lit/ds/symlink/tpa6132a2.pdf)
which verified that to be the case.

<center>![TPA6132A2 QFN Pinout](/img/headphone-fix/TPA6132A2.png)</center>

**Bingo!** Now knowing the pinout, I could use my trusty multimeter (_a Fluke
115_) to test continuity of the circuit from the known-good and the now
known-bad speaker traces back to the `OUTL` and `OUTR` outputs of the amplifier.

{{% admonition info %}}
![Tweezers](/img/headphone-fix/IMG_7514.jpg)
{{% /admonition %}}

Removing the board from the housing required a bit of finesse. I didn't want to
bother desoldering the left speaker connections to make removal easier. So, with
a bit of gentle back and forth I was able to get it the PCB out and inspect
traces on the bottom side.


# Something's Not Quite Right...
Continuity from `SPKL+` to the QFN pin was good, yet `SPKR+` to the op-amp
showed open circuit. Visibly, everything on the PCB looked fine. There were no
apparent signs of damaged or lifted traces, nor bad soldered wires or
pins. Somehow the trace shortly after the chip was damaged in a way that
resulted in an open circuit at the point of the right speaker's solder pad.

After a few minutes of scratching my head and repeatedly going over the
datasheet to check for any misunderstandings on my part, I realized the cause of
the issue didn't matter so much. The objective was to fix the unit. I simply
needed to re-establish the connection for `SPKR+` to the chip.

Using the 3.5mm mini-jack's solder pads, I found continuity to be true from the
chips left and right outputs to the conveniently accessible solder pads. _A
bodge wire was in order_..

{{% admonition info %}}
![Look closelier..](/img/headphone-fix/IMG_7515.jpg)
{{% /admonition %}}


# All's Well That Ends Well
Again, using my trusty Fluke 115, I verified continuity from the chip's `OUTR`
pin to `SPKR+`. Lo and behold it was now closed-circuit! I was very happy to see
the expected waveform from the known-good left channel now also appearing on the
right channel.

{{% admonition info %}}
![Happy Scope](/img/headphone-fix/IMG_7516.jpg)
{{% /admonition %}}

At this point I quickly re-soldered the wires to the speaker and enjoyed music
now coming into both ears!