Sunday, August 22, 2010

Repairs to a DRE-4000 Aviation Headset

Since getting my ticket back in 2004, I’ve been using a pair of DRE headsets in the local FBO’s Skyhawk.  The headsets have worked quite well considering the $150 entry price.
A little over a year ago, I noticed that the cord was beginning to fray.  At that point, there were no usability problems, just cosmetic, but it was obvious that it wouldn’t last forever.
Sure enough, one spring afternoon I loaded up the plane, and one the lucky passenger had no Mic audio.  He could hear, but not talk.
I priced around a little bit, and I can buy a replacement cord for about $35.  Add shipping to that, and you’re not too far away from a down payment on a brand new headset.  Instead I decided to dig in and see if a repair was possible.
One of the things that I do like about the DRE’s is that the cord is replaceable with two thumb screws.  I pulled the plug, which allowed me remove the cover over the wires.
Obviously the yellow wire has a problem.  It’s impossible to visually inspect if any of the other wires have issues since they’ve been potted in some sort of resin.  The bad part about this type of design is vibration and movement of the of the potting material can cause the solder joints to break or become intermittent deep inside where they can’t be inspected or repaired.
Begin by taking a pair of pliers and break up the resin that’s encasing the existing wires.  Don’t break the connector itself, but the wires will all have to be re-soldered, so don’t worry about them.
When making a repair like this, it’s best to cut the top couple of inches off of the cable and start fresh.  Begin by putting the outer shell of the connector back on the wire (near my thumb).  Strip the outer insulation back about an inch to expose the wires.  Cut the braid off flush with the outer insulation.  (Notice the “key” shown here on the shell of the connector.  This keeps the connector from only being inserted in one direction, and is critical in later steps.)
Separate the wires, and strip back about 1/8” of insulation on each.  Tin them with solder.  Also prepare the connector (at right) by tinning the pins and removing any old wire that may have been left.
Before final assembly, notice that there are two sides to the connectors, and that it will only fit into the headset one direction.  The order shown here is with the “key” at the back (not visible) of the photo.
DISCLAIMER: Fortunately, I had a second identical headset that I was able to ring the wires and connectors to determine the proper sequence of colors.  There’s no guarantees that these colors are the same for any other DRE-4000 headset, but they probably are.  If in doubt, consult your avionics shop.
The order (from left to right, with the key in the back) is Red, White, Brown, Green, Black.   Solder the wires to the pins, making sure that the shell has already been placed over the cable and is ready to be slid into position.
Like I said earlier, I really don’t like the potted connector/strain-relief solutions, but unfortunately there aren’t many options with this particular design.  Once you are comfortable with your solder work, mix up some 5-minute epoxy and drizzle it into the connector shell.  This epoxy is the only thing keeping the wires from being ripped out, so use plenty.
Finish pulling the shell down over the connector and then apply gentle pressure to the sides (I used clothes pins) to keep everything tight while it cures.  The hole in the headset that this connector fits into is fairly tight, so keeping pressure on it during the curing process is essential.
That’s it.  Once it has cured, re-insert the plug into the headset, and replace the thumb screws.  If the wiring was correct, you should be good to go for a couple more years.  If it wasn’t correct, I’m sorry to tell you that you probably won’t be able to fix it.  The plastic used on my plug was just barely strong enough to survive one reconstructive surgery, and I don’t expect it to make it through a second.
Happy Flying!