I recently won a bargain Ebay auction for 4 x Hytera SM18N4-Ex hoping they would work with my PD785 handhelds. Unfortunately, I was wrong but the good news is that I did manage to figure out how to make them work!
There’s 2 ways to do it, one is the no damage approach, the other involves a destructive modification
but could be reversible.
To start off, I connected a standard SM18N4-Ex to the PD785 and was met with this…
The PTT worked but the microphone speaker on the SM18N4-Ex did not. I noticed that it I loosened the connector and moved it around a little then I could get the “Accessory Connected” message and the SM18N4-Ex would work fine but it was very difficult to hold the plug in that position.
Next, I looked at the pinout for the accessory connector and noticed that pin 3,4 and 13 were all there to identify the accessory.
After a little experimenting and with the help of Google Image Search, I figured out that pin 3 and pin 13 were extra pins on the Ex range of speaker microphones. Now, let’s get this microphone working with the PD785.
The non-destructive method
This method places 2 small pieces of a good quality insulation tape (Scotch Super 88 is good) over the contacts for pin 3 and 13 on the radio accessory socket.
It works great and detects the SM18N4-Ex as a valid accessory.
The drawback with this method is that you will need to remove the tape from pin 13 in order to program the radio and may need to remove the tape from both pins to use other accessories. Not a big problem if you don’t reprogram your radios often.
The destructive method
Well, I do like a bit of destruction so I had a go at the destructive method too! For this method, you just need to pull out pin 3 and 13 from the accessory plug. The pins are spring loaded and slide inside a tube that is molded in to the plug. They come out very easily with a small tug on a pair of needle nosed pliers. I think you may be able to put them back in to reverse the modification but make sure you catch the tiny spring that shoots out if you want to do this in future!
Both methods work well and I’ve tested all of the functions of the microphone. This could be a great way of picking up a cheap Ex accessory (which seem to sell much cheaper than the non-Ex versions) for your Hytera handheld.