What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

How to test DSUB connectors and harnesses

PaulvS

Well Known Member
I'd like to test some DSUB connectors and harnesses that are installed in the aircraft, for correct polarity and continuity, before plugging into the expensive EFIS and EMS boxes. This is for a Dynon system with DB37, DB25 and DB9 connectors. The radio will use DB15 connectors. It's fiddly to use a multimeter probe on the Dsub pins, so I'm thinking there must be a better way to get access e.g. by using a breakout plug or board. Before buying some bare plugs and warming the soldering iron I'd like to know what other builders might have done?
Thanks
Paul.
 
Make a pair of test leads with D-Sub pins and sockets on the end of two-foot-long pieces of wire. Then you can slip them on the pins (or in the sockets) one at a time at each end of the cable to check that everything is where it should be, and that you have continuity. If you need to get deep back into a radio tray, tape them onto an insulated piece of hinge pin a foot long so you can reach in from the front of the tray.

You can be fancy and make the leads with banana plugs on the meter side so that you can plug them into a DVM directly, or just have bare wire that you connect with clip leads to your DVM.

Paul
 
What I've done is to just buy solder-cup connectors that mate with the harness spots you want to test. Putting a multimeter lead into one of those solder cup terminals is still a little fiddly, but much less so than trying to actually hit a pin or socket in a connector.
 
For the Dynon system, I built the serial wire harness and did continuity check for each of the pins. This is the easy wire harness to build and test since all of them will have the same 8-wire pins. The only serial harness that has 9 is the EMS.

For the rest of the wires for the transponder, radio, intercom, I built most of harnesses and tested the EFIS+units while they are on the bench. I was a complete beginner at this so having everything on the bench helped me to debug. It turned out, most everything went together well the first time. The only problem was the wiring for the intercom, with the multitude of solder connections, and complicated wiring diagram, I had to redo this wiring after discovering I did not have radio com.

I strategized powering up the different units individually and incrementally connected more units to the main EFIS. The main EFIS only need 2 power wires and ground wires. You get the "X" on the screen but as you add more stuff, like ADHARS via the serial cable, you start to see the attitude indicators. This worked for me. I remember the sequence was EFIS, +ADHARS, +GPS, +ADSB, +RADIO, +INTERCOM. The intercom was last since it was the most complicated for me wire.

After all the avionic units could "talk" to each other, I mounted them plane. The EMS wiring was completed on the plane since the wiring needed the engine and most of the avionics in place. One mistake was I didn't have the service length as much as I would like. It was enough but I rather have more length.

Some of the pros did all of this with everything connected to the panel, and did the wiring while sitting inside the cockpit. I could never have tried since my chance of making mistakes will go up exponentially.

I planned one month for this task but it took me more than 3 months since I was trying to learn the wiring diagram and the airplane electrical system.
 
I made two long test leads with DSUB pins. I tested all the powers and all the grounds for my avionics. Then I fired up the devices. I just had a few problems - one spade connector was not doing the job on a ground and I had a power wire that disconnected and shorted out the inline fuse on a CO detector.
 
Thanks for ideas

Thanks for the replies, there's some techniques mentioned that should be useful. I also just got a 9 pin male-male adapter to help with using the 10 foot network test cable that came in the Dynon package.
 
I've been guilty of just poking a piece of safety wire into the pin sockets on one end, hooking to that, and just touching the pin with a probe on the other end.
 
Mikeyb

That is the best thing for Sub-D harness testing I have seen. Much better than jumper wires.

Thanks.

GM

Another trick is use a commercial D sub breakout board. The screw terminals are easy to probe and identify. They are fairly available. If you need to get to a hard to get to connector you can use a commercial cable between the connector and the breakout board.

[
 
Last edited:
One caveat I should have added. When probing the break out board screw heads make sure the screw is tight and there is contact between the screw itself and the contact.
 
Back
Top