All Things Wireless & Letterpress

All Things Wireless & Letterpress

Sunday, January 11, 2015

Replacing the HTX-252 Mic Cord

If you purchased a Radio Shack HTX-252 sometime 2004 or 5, you've had it for some time.  You probably already know about the disintegrating microphone cord.  Wow, and it is a thorough disintegration, too!  I don't think I have seen any piece of apparatus fly to pieces quite like this cord!  Not only the external coiled vinyl jacket, but the interior wiring insulation as well.  Check out the photo above!  Every wire in this eight-conductor cable shorted.  The insulation came to pieces at the very touch!  And this rig was stored in a climate controlled environment!!

I combed the Internet, Craig's list, E-bay, E-ham, you name it, no go on a replacement mic.  In fact, all the HTX-252s that I have seen for sale all have the same problem with the microphone.  A lot of listings do not mention it, but I can see by the photos their mics are not long for this world.  Thus, a new microphone is out of the question.

This presents a problem because the HTX-252 is largely controlled via the microphone, which serves as a sort of control head.  I really don't like these arrangements, I like to purchase name brand mics, it would have been nice to get a nice Electovoice or Turner or Astatic mobile mic for this rig!  Not that the sound produced by these mics are bad, but sometimes it's just nice to hold a traditional mobile hand mic.

As such, the only recourse I had was to replace the cable and try to salvage the mic head and 8-socket plug.  And this is where we pick up in this installment.  Replacing the cable.  

I ordered a nine-conductor mic cable from one of the many suppliers on line.  The colours in this cable very nearly matches the original, which is Red, Black, White, Brown, Blue, Green, Yellow, and Shield.  While the photo from the supplier showed a coiled cord . . . it did not arrive that way.  Oh, well . . . . it was still a nice cord.  The cable jacket is a rubberised polymer that seems pretty durable, but time will tell.  So did the original.

The first thing I did was to decapitate the cord, removing the head and the plug. The wires were pretty shredded, and I wanted to use the remaining wire stubs to serve as a wire colour guide to help me keep from an accidental mis-wiring.  Soldering eight wire cable is a far cry from my usual four conductor Astatics and Shures.

As an added precaution, I drew the wire connects on both the plug and the microphone soldering points.  And since these days cameras are on the phone, I took photos as well.  Just an added precaution against mistakes.

This is the mic head with the back cover removed to show the solder points.  Easy access, but a very fine soldering head must be used.  I used a copper tack fitted into my 15 watt soldering pencil to do the job.

The first thing I did was to measure and cut back the cable jacket, carefully.  As it was, the shield on this cable actually came woven around the eight inner wire conductors, so I had to unweave the braid, which was pretty easy, using a pencil to separate the copper shielding braid wires, and then winding them together into a single wire.  Then I trimmed back the insulation of each wire, and tinned all the tips, both sides.  A "third hand" clip holder comes in handy for this.

Holding the plug with one clip on the "Third Hand" holder, and bracing the cable with the other clip left my hands free to remove the old wiring one by one, resoldering in it's place a matching coloured wire, one at a time, all the way around the plug.  About half way through I soldered the shield/ ground, which was the center pin.  I did it at this point, while I could still easily reach the soldering tip to the center pin without endangering any nearby wires.  Be sure your collar and plug shell is already on the cable BEFORE you solder.  Otherwise you may find yourself unsoldering your pains-taking work and re-soldering.

The soldering to the plug pins are done, the collar and sleeve are screwed on, now we go to the other end of the cable, the Mic Head.

Only two screws hold the back cover on.  Remove them, lift the cover from the bottom.  Remember that you have not only a PTT switch, but two buttons on the top of the mic as well.

Back cover is removed, and we can see where all the wires go by their colours.  The top of the cord turned out to be not quite so disintegrated as the plug was.  We do the same thing here, remove one wire, solder the new one in it's place, then the second, then the third.  The solder connects are very close together, be careful not to bridge a connection with a solder blob.  Pre tin your new wires, of course.  Go sparingly on the solder.

In due course, all the wiring is soldered.  The spaces between the solder has been checked with a razor blade to make sure no bridged gaps exist.  All that orang-y stuff you see is old solder flux from the original soldering job.

Watch the cable jacket.  I needed to pull mine back just a touch so the cover could go back on.  The cover pinches the wire somewhat, in order to hold them in place.  As you screw the cover back on, the pressure from the back squeezes the cable just a bit, creating a pretty good hold!

After this, the "smoke test".  Mine worked the first time, no errors in wiring.  I do have to apply a bit of DeOxit to the volume and squelch control, but other than that, the HTX-252 works like a champ, with all mic controls functioning.  And because the mic works - so does the radio itself!

I now have a "new" 20-watt two-meter mobile!  
I hope this little show - and - tell session helps you out.  It's pretty self explanatory, just follow the wire colours and keep them succession.  You won't mess up! 
See you on 146.580 Simplex!

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