LEMO wiring oddity

[Midengineracer]

I am installing a new radio in my plane and have come across quite an oddity.

Verifying wiring to the GIB position, this is what the multimeter gave me:

Pins 3 & 4 go to wires in a shielded cable,
Pins 1 & 2 go to wires in another shielded cable (should have been to the red and black power lines),
Pins 5 & 6 go to the shield of a cable.

1&2 are VDC+ and ground,
3&4 are HS left and right,
5&6 are the mic.

This was originally wired to an ICOM A210 and the radio was mono with one output that fed both pilot and copilot positions.  This was sent to what I believe was a space saver panel?

Still, I don't know how the headset was functioning, at all back there.  I checked my results several times, but got the same result.  I'll be checking again next time I go to work on the plane.

I've ordered a new LEMO jack, but I am dreading trying to pull the wiring through the pilot seatback, especially since the wiring will have to be extended on a new jack to get to the junction I need to tie into.

Anybody got some input on this?

[Kent Ashton]

Here is the wiring for the A210.  It might help you determine what's what.  You will see that power wires and PTT wires are not shielded but audio wires use shields.  Headphone and mic jacks use the shields as a return path but perhaps the last guyused a two-wire connection to mic & headphone jacks with shields over them.

https://www.ameradio.com/doc/Icom_IC-A210_installation_guide.pdf

[Midengineracer]

Kent, 

Thanks for the diagram. I used that when working my way through this, but there are some real oddities in the installation. 

For one, there was no copilot mic connection at the radio. 

The PTT was the only connection on pin 8, even though it should have had the ground for both microphones as well.

I think everything got grounded at that space saver panel instead. 

Regardless of those oddities, I don't get how the LEMO was functioning, but I measure the positive and negative pins as being in the shield. 

I'm going back today, I have all my materials for everything else. I am going to retrace the GIB connections first, while I'm fresh and ensure I'm reading the pins correctly.

I have many sheets with different wiring setups labeled space saver, but none dal in enough detail about the audio panel portion...

[Kent Ashton]

It would seem easy to wire your PTTs so that either button activates the function (pic)

BTW, what is a LEMO?

[Midengineracer]

Yes, wiring like that would work and be appropriate for the ICOM radio (I think) . The Garmin GTR200 going in its place separates the mic and PTT for each position.

LEMO connectors are the round, 6-pin connectors that will provide power to some noise canceling headsets so you don't go through batteries. Some people call them Bose connectors, but David Clark and others use it to. I think LEMO is actually a brand name, still. 

[Midengineracer]

Alright, with a clearer head, I did more digging and I believe I have this solved. 

All shield and ground wires for both headsets were going to a single ground point that was on the airframe, not the radio. 

I found the common ground, disconnected it, and all seems right in the wiring now. 

The issue I was having is an example of why all audio connections should go to a single ground point on the audio system, it prevents ground loops and strange audio problems. 

I'm convinced the new setup will sound great when I finish, now. 

Thank you for the responses Kent.