Saturday, April 21, 2012

Third-party Kenwood accessories

Ebay is a good place to buy accessories like speaker/mics and headsets for your radios. A few years ago I used it to buy a speaker/mic for my Kenwood TH-F7E. After I sold that radio I used the speaker/mic with my TH-D72. When I tried it with my old TH-205E however I found that PTT didn't work. I soon established that the reason was the genuine Kenwood accessories used a monophonic 2.5mm plug with only two contacts, tip and sleeve, for mic audio and PTT. The third-party accessories from eBay used a stereo 2.5mm plug with tip, ring and sleeve, but there was no connection to the ring. It looked as if the plug in the radio was trying to make contact in the area of the ring. This obviously was OK for newer Kenwood radios but with the 205E there was no ground connection for the PTT.

Ring and sleeve of the 2.5mm plug should be connected

My first thought was to open up the speaker mic, find the wire connected to the ring and connect it to ground. However I soon found that the cable of my speaker/mic had no wire connected to the ring at all. My only option was to try to bridge the two contacts together using solder. This I did, and the speaker/mic then worked with the TH-205E.

The Wouxun KG-699E and the Baofeng UV-3R+ also claim to use accessories with a Kenwood-compatible plug but just like the 205E I found that PTT did not work. I have just performed the same modification to the plugs on a "Kenwood-compatible" headset/boom mic and also one of the earpiece/mics that came with the Baofeng and Wouxun so that they would all work with all four radios. It is easy to do, but you need to take care as it's easy to melt the plastic parts of the plug and you could easily ruin it if too much heat is used.

Using a sharp craft knife cut away a small section of the black plastic insulation between the ring and the sleeve of the 2.5mm plug to reveal an inner metal sleeve. Open this up a bit more using the edge of a jeweller's file. Then make a solder bridge between the ring and sleeve. You need to apply heat using the edge of the soldering iron bit to the inner sleeve in order that the solder will bridge the gap. Apply the soldering iron for as short a time as possible to avoid melting the plastic insulation and destroying the plug. I used Blu-Tac to hold the plug in a steady position whilst soldering.

After you have bridged the contacts use a jeweller's file to remove any excess solder from the plug. You should also smooth the plastic insulation between the plug contacts which may have melted and bulged a bit. The plug should be completely smooth between the contacts, the solder bridge and the insulation. It should plug easily into the socket on the radio. If it needs a firm push then try a bit more filing until it goes in easily. You don't want the plug to get stuck in the radio nor for it to damage the socket contacts if force is needed to insert or remove it.

I accept no responsibility for damaged plugs or radios as a result of trying this modification. However I have done three of them now with success each time so it is possible with care. Now my "Kenwood-compatible" accessories will work with old and new Kenwoods as well as the Baofeng and the Wouxun.
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