Swapping an AC adaptor plug

We made a decision to settle on 2.5mm diameter barrel jacks for all of our products. However, many adaptors come with the common 2.1mm plug. In some of our kits we’ve started providing a replacement 2.5mm plug so that you’ve got a wider choice of which adaptor to buy, This article shows you how to replace the barrel jack on the cable for an AC adaptor.

Important note: This guide shows replacement for an AC output adaptor, where polarity isn’t an issue. DO NOT use this guide to replace a jack for a DC output adaptor, as this would require that you maintain the correct polarity; this guide would therefore only give you a fifty-fifty chance of success.

Parts & tools

_MG_7700_thumbYou’ll need a replacement jack of the correct diameter and of course the adaptor that you want to replace! You’ll also need a soldering iron, solder, snips, pliers and something to strip insulation with. A “helping-hands”-style stand might also be useful.


_MG_7701_thumbUnscrew the barrel of the replacement jack from the plastic body. Snip the jack off the adaptor cable, then separate the wires and strip a centimetre or so of insulation from each strand. Twist the copper strands together, and then tin them with solder.

The really, really important bit

_MG_7702_thumbBefore you do anything else, fit the plastic body of the replacement jack onto the cable, ensure it’s the right way round. It may sound trivial, but this step is super-important – you don’t want to do a lovely neat job of soldering your barrel into place only to find you have to undo the whole thing in order to put the body on.

Solder the new jack into place

_MG_7703_thumbTease the contacts of the new barrel apart a little in order to give yourself room to work. Thread a tinned end of each wire through the holes in the jack’s contacts, then applying heat to both the wire and the contact, solder them into place. Remember that this is an AC output adaptor – current flows alternately in both directions through the jack – so it doesn’t matter which wire goes to which contact. Snip off any excess wire after the soldered parts have cooled.

Finish off

_MG_7705_thumbRe-settle the contacts back to their original positions. If there’s a strain-relief wire grip built into the outside contact, use pliers to bend this around the wire to secure it in place. Finally, slide the plastic body over the soldered contacts and screw it back into place around the barrel – take care to rotate the body part not the barrel, as doing so will twist the wire and possibly put strain on your soldered connections.

Finally, plug the adaptor into mains and give the output a test with you multi-meter (make sure you use the Volts AC setting to measure with). All good? Excellent, your adaptor is now ready to use!