Repairing a headphone lead: Sennheiser PX100
Posted by Howard Richardson (comments: 11)
I love my Sennheiser PX100 headphones, but I seem to get through at least a pair a year. The trouble is that the lead on them breaks all too easily if it gets caught on something. It only needs one tug and the delicate copper threads in the cable can break and then one or both ears stop working.
This time instead of shell out another £40 (for the even more breakable PX100ii version), I decided to repair some old ones. I had two pairs of broken PX100s and another pair of HD 202s with a ridiculously long cable. From all three I got enough parts to fix up one new working set of PX100s. This is how I did it...
You will need:
A replacement plug (if your cable is missing one), a multimeter, broken PX100s, a replacement headphone lead, soldering equipment + solder & flux, a craft knife, a lighter, plus wire-strippers and a normal kitchen knife (not pictured!)
For your replacement lead it's important to get the right type of cable. Normal audio leads will be either noisy, too thick or inflexible, so I took my replacement lead off an unwanted pair of Sennheiser HD202 headphones. Because you'll want to split the cable into two at the headphone end, you should take the little grey sliding bit off your old PX100s and slide it onto the new cable. This makes a great block so that the lead doesn't split all the way back to the plug:
Opening the speakers
You'll need two working PX100 speaker units. Usually these aren't the parts which get damaged, so if you're lucky you'll still have both working. The speaker units can be quite tricky to open because they're glued shut. The glue is the soft type though, and with a little gentle force, they can be made to open.
Firstly you can try and scrape away any extra glue you see around the edges of the speaker unit with the craft knife, where the grey and black parts join.
Don't spent too much time doing this though, because the majority of the glue is already inside the unit where you can't get to it. Just clear away what you can without damaging the case.
Next you need to lever the black cover off the grey body with the tip of a strong knife. Insert the knife above where the cable enters the unit and gently try to prise a little space free between the two parts.
You're not trying to get the two parts fully separated yet. You just want to make enough space so that you can then use the knife to lever the rest apart sideways, like so...
Here I'm using the blunt edge of the knife and levering sideways, working my way around the circumference of the unit until all edges become free. If you do this you should be able to remove the black covers and see this:
Set your speakers aside now, and we'll work on the cable.
Soldering the lead and plug
At the one end of the cable we want to solder a new plug. I had a spare Neutrik plug, used before but still salvageable. The problem with the type of wire that is used on headphones is that the strands in the wire are coated with a lacquer which can't be soldered directly. There is also a fibre-glass type fuzzy core, around which the strands of wire are wrapped. What we have to do is strip away the lacquer and remove the fuzzy core. You can just about see the red lacquer and white core here:
Your tool for accomplishing this is a normal lighter. Spread the strands of the wire out as wide as you can get them and then burn the tip of the wire quickly with the blue part of the flame. The fibre core should burn away quickly and the lacquer on the wires will turn black. Don't burn them too long. If the wires start to glow red with heat, you've burnt it too much! Afterwards your wire will look something like this:
Now using the craft knife, gently lay the wire on a flat surface and scrape away the soot and burnt lacquer off the end of the wire. You should use a very gentle pressure and strokes only in one direction. It make take 30 or 40 strokes to clean the wire properly. Turn it over and do both sides until the end of the wire starts to shine a copper colour.
The end of this wire is now solderable. However, I've found it doesn't take the solder well at all because of the material. An optional step now, which will improve your chances of getting a good solder joint, is to take a single strand from a normal wire. These strands are a silver colour, not copper. Take a strand and carefully wrap it round and round the copper strands, working your way right up to the tip. You'll have something that looks like this when you're done:
Now you can dab a bit of flux on these and tin them with your soldering iron. You'll find they take the solder easily. Afterwards you can trim them down so they look neat and there's no blobs of solder. Make sure also that no ends of the wrapping wire are left poking out. Here's one I did earlier:
You'll need to do the same process for the copper-coloured ground wires too. On the plug end you can then join these two together when you wrap them so they form one single contact. Now you can use your three contacts and solder them into the plug, like so. (Warning I made a messy soldering job - not for purists!)
Screw the sleeve back on and your plug should be done..
Now go and do the burning and scraping at the other end of the cable, then get out your multimeter and check that the connections are going to the correct poles on the plug, and also that nothing is shorting out. If it is, you'll have to go back and open up the plug and fix it.
Wrapping the exposed copper strands I found not to be necessary at the headphone end of the wire, but you might want to do it anyway. It's up to you.
Putting it all together again
Now with the soldering iron, unsolder the old factory connections from the speakers so you have two bare contacts ready to be used...
On the lead, split it down the right amount so that the V hangs just below your chin. The wires should be equal length too.
Next, tie a small knot as close to the end of each of the wires as you can. This knot we will leave inside the speaker unit so that if the cables get pulled, the stress goes on the knot, not on the solder joint.
Now you're ready to solder the wires onto the speakers with a blob of solder, just on the exposed tip of the wire. The coloured wire is closest to the centre. Again, I've done a messy-looking job here, but it's electrically sound, and that's the main thing.
At this point you should be able to plug in your headphones and play something through them carefully, to test that they're working.
If they are, you're ready to reassemble the speakers. Pressing the knot inside the case and threading the cable out through the hole, push the two halves of your speaker back together. Here you can see the knot inside:
I've found you don't need any more glue to hold the two halves together. They seem to just stay in one piece with the glue that's already there, but if yours easily fall apart a dab from a hot glue gun inside the speaker should do the trick.
The finished product
Fit your two speakers back together and then fit the cushions over the top, and you should have the finished product.
Voilà! One completely repaired pair of PX100s. Happy listening!