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Topic: Repair proof headphones? (Read 1 time) previous topic - next topic

buffer_overfly

May 07, 2016, 03:24 pm Last Edit: May 07, 2016, 03:31 pm by buffer_overfly
I was trying to repair a pair of headphones. The cables are severed near the jack connector. So I cut a good 5cm above the damaged point and peel the cables. There are 4 wires: red (R-channel), green (L-channel), and two orange ones (GND).

Here you can see a picture of them:


To remove the insulation I burned them slightly. It was a good burn, the fire stopped right in the peeled part and the black cover was not melted. Then I cleaned the black stuff with rubbing alcohol.

So far so good, now I start the soldering. I wanted to plate the wires first, and here comes the first surprise: they don't get wet at all. The solder just doesn't stick to the wires. I'm starting to think maybe I've just burned the wires and I'm trying to plate the insulation instead, but it just doesn't make sense. These wires, or whatever they are, are rigid and able to sustain the heat of the molten solder for long time.

I was so screwed up I just went ahead with a cold joint. After all, I just needed no stick the wires to the replacement plug.
After the soldering is finished, I take my multimeter and start checking for shorts in the 3.5mm jack. Here it comes the second surprise: everything is shorted to everything!  :o R is shorted to GND, L is shorted to GND, and of course R and L are also shortened between them.
After inspecting the damn thing for 10 minutes using a magnifying glass, I arrive to the conclusion that the soldering is ok and therefore the short must be upwards in the cable. I desolder everything again and check the jack: no shorts on it.

So I cut a good chunk of cable and peel it again, and fire the tip of the wires. Then I check for connectivity in the tip of each wire using a multimeter, and it is non-conductive  :o  I'm starting to lost my sanity as this just contradicts what I saw earlier. Either the wires are conductive and they cause the short, or they are not conductive and I'm somehow damaging them with the fire.

So I cut again another chunk of cable and peel it, but this time I carefully remove the insulation fibers by hand. Then check again with the multimeter, and still no conductivity in the tip of the peeled wire!!

Here's a picture of the original audio jack. As you can see, the wires must have some insulation covering them as they are mixed together, and only in the final 3mm they get attached to the metallic terminals of the jack with what seems to be a bit of solder:



What is going on here? What kind of repair-proof material are these wires made, so that they are able to resist the heat and be conductive in the inside but cannot be soldered?
The competent programmer is fully aware of the strictly limited size of his own skull...(E.W.Dijkstra) (dammit only 140 chars?)

DVDdoug

It/s probably Litz wire, where the individual strands are enamel insulated.     I've never had any luck soldering the stuff.      I found this website with some suggestions.

buffer_overfly

It/s probably Litz wire, where the individual strands are enamel insulated.     I've never had any luck soldering the stuff.      I found this website with some suggestions.
Exactly! I discovered myself this before reading your reply. Each single strand is coated with insulating paint. I needed to burn the nylon and then untwist the strands and sand each one carefully. Earphone makers must be really bad people. BTW I didn't know the dmna thing had a name! Thanks for the link.

And now about the multimeter issue. After properly re-soldering everything for second time, I checked for shorts and again R, L and GND were shorted between them. I thought I had done something wrong again. But my soldering skills are getting better, and GND was physically insulated using rubber strip. So then I thought, what if the shorting of the terminals were actually normal for headphones? I tested another pair of headphones and I observed the same result. :) Silly me, earphones are the moving coil type! What the heck was I thinking.
The competent programmer is fully aware of the strictly limited size of his own skull...(E.W.Dijkstra) (dammit only 140 chars?)

Grumpy_Mike

Quote
Earphone makers must be really bad people.
They don't do this just to make thing difficult to repair. They do this to improve the reliability and quality of the headphones. Without this sort of wire the constant flexing of the wire can snap it with metal fatigue. If the strands were not insulated then the rubbing of the wires against each other would cause noise in the headphones.

It is a lot cheaper to use normal wire than Litz so the manufacturers are not saving money but spending it to give you a quality product.   

polymorph

Burn the wires... why? Usually the insulation is made to melt off at soldering temperatures. You have likely oxidized the surface of the wires by burning them.

It is also possible that some of the tiny wires got crossed between bundles.
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