Replacing the 4 Wire Phone Plug for a Smartphone Headset: Hints and Tips

Replacement 3.5mm 4 connector headphone jack, varnish, shrink wrap, new jack completed, Photo 05 by Don Tai.

After many years of careful use, the headset that came with a long gone Blackberry smartphone lost sound in the right ear. If I wiggled it “just so” the sound would reappear, but with any further movement the sound would again be gone. It was clear that the wire would need to be cut back and the 3.5mm phone plug would need to be replaced. Because I do like the feel and the quality of the headset and mic, this was worthwhile to repair.

From past experience I knew that this would be a a tedious job. The smartphone headset had an additional microphone, which results in a 4 wire plug. Further the cable with the headset is a flat ribbon, which I have never repaired before.

From watching Youtube vids, it was clear that there was no set colour scheme for a headset phone plug. Any colour can go to any terminal. The phone plug’s pin configuration, from the plug tip is left channel, right channel, ground, and then mic. The soldered ends, from the middle of the plug are exact opposite: mic, right, left, ground.

It turns out that my wires were copper (mic), red, green, dark copper (ground), completely different from the others I have seen. As with the others, all wires have a lacquer coating, so when I probed them with a multimeter they did not conduct.

Replacement 3.5mm 4 connector headphone jack, cut defective jack, Photo 04 by Don Tai.

Strip the existing plug
There are 4 wires and no instructions as to which wire goes where. It is also obvious that worldwide manufacturers use all different colours of wire. I took a sharp knife and cut lengthwise the existing phone plug, and stripped off the outer rubber. This allowed me to see through the semi-transparent epoxy to the wires.

Replacement 3.5mm 4 connector headphone jack, partially strip outer insulation to see wire colours. Photo 03 by Don Tai.

Replacement 3.5mm 4 connector headphone jack, partially strip outer insulation to see wire colours. Photo 02 by Don Tai.

Apart from breathing solder fumes, this is the most dangerous part of the job. Be careful with your knife.

Replacement 3.5mm 4 connector headphone jack, cut defective jack, epoxy is transparent so you can see which wire colours go to which contacts, Photo 06 by Don Tai.

Replacement 3.5mm 4 connector headphone jack replacement, cut defective jack, epoxy is transparent so you can see which wire colours go to which contacts, from center outward is copper, red, green, dark copper, Photo 07 by Don Tai.

Stripping the Outer Rubber Casing
Stripping the outer rubber casing was easier than I thought, but you really need to be careful to not cut any of the wires. All wires are multi-stranded and extremely thin. I had to do a very shallow cut, then bend the wire back a bit and slowly cut deeper, until all wires were exposed but not cut through. Do shallow cuts on either side. Turn over and do a shallow cut, bend, cut deeper. If you inadvertently cut some wires, then start over a bit higher up. These wires are so thin that you really do need all of them for good sound transmission.

Replacement 3.5mm 4 connector headphone jack, defective jack and outer insulation cut away, new jack is 90 degree right angle, Photo 01 by Don Tai.

Thread on the phone plug strain relief end and heat shrink
This is the only time you may be able to thread the phone plug strain relief end and heat shrink onto the wire. Ensure the strain relief is on in the right direction. If you forget to do this and then solder you wires, you’ll either need to unsolder or go without the strain relief and heat shrink.

Burning off the Wire Varnish
Lay the wires out as separate as possible. All wires are coated with varnish and are thus not easy to solder. You can test this with a multimeter by measuring conductivity on any of the obviously connected wires. They will all say zero. I used a lighter to ignite the varnish, which is easily done. The varnish creates an immediate flame, so blow it out right away. Do this at the end of the wire as well as where you intend to solder, and you’ll see there is now conductivity. The wire turns a bit brown, the wire colours are not as bright.

Tin the wires and the new plug contacts.
To hold the plug stationary, I used a block of wood and drilled a hole smaller than the size of the plug, so the plug will fit tightly. This is your vice.

Heat up and clean the tip of your iron really well, then tin it. Tin the wires and the plug contacts. This should make it easier for the wires to stick. I’m not very good at this, and also not very accurate.

The replacement 3.5mm phone jack was from Philmore, no 70-045, made in Japan. I paid $6.50CAD and picked it up at the store during the pandemic. As they only had a single version, I had no other choice. The plug has a small plastic clip that opens, allowing the strain relief and the metal contact unit to be removed. The plug contacts are small, so there’s not much room for mistakes in soldering. I don’t think the plastic strain relief will do much. I’d have preferred an all metal plug, but this did the trick, and black matched my existing headset. The 90 degree right angle is easier to use and provides better protection with a smartphone or laptop.

Solder
I soldered the outer ground first. This is the shortest wire and holds the cable to the phone plug. I then clamped the rest of the wire to the wood block.

Soldering the rest is the difficult part. The pins are small, the wires are thin. I found I had to add some thin solder to the contacts, and often messed up the plastic separation between pins. I also turned the plug and solder the other side of each contact, for a more secure connection.

Wait for the solder to set, then plug into a computer or phone and test.

Cleanup
Once you are certain the connections are electrically solid, you can then add some clear nail polish to all exposed wires. This will insulate them and also glues them down. Heat up your heatshrink, add your strain relief and outer plug, and you’re done.

Replacement 3.5mm 4 connector headphone jack, varnish, shrink wrap, new jack completed, Photo 05 by Don Tai.

Replacing a 4 connector phone plug sounds easy, but there’s not much space in there. The wires are really thin and easily damaged, and there are a lot of steps you need to know. For example, all wires are lacquered and will not conduct! Once you do it, hopefully you’ll not need to do it again for a good long while.