Audio jack ground loop(??)

TLDR

• Upholstered the rear fuselage rib
• Discovered potential ground loop issue when reconnecting audio jacks

Detail

Upholstery

I don’t remember the source, but I was looking at someone else’s picture on the rear section and realized I forgot to glue on the leather skin for the rear fuselage skin. That’s the skin going over the rib behind rear passenger door.

This rib happens to also host the 4 audio jacks for the rear seats.

So I removed the 4 audio jacks, and used cement concrete to glue the leather skin on. During this process I also used my solder iron to poke holes for the rivnuts and audio jacks on this rib.

Audio jack issue?

I put a question mark on this section because at this point I still don’t know if I really have a problem. I hope not.

So, when I re-install the audio jacks, I pulled out my multimeter and tested the barrel to airframe ground. I expected to have none.

However, three of the 4 barrels on the rear had no continuity but 1 did. That’s the one I was holding in hand in the picture above. I even tested it without attaching to the air frame, still showed continuity to airframe ground. That’s strange.

I asked my trusty advisor Midwest Panel Builders. They said the barrels will seek ground through GMA245, which was in fact connected when I was testing.

Well, then I would expect all 4 barrels to test positive to ground, not just one.

This is pretty confusing. Either I have one barrel with ground looping, or I have 3 not properly grounded. Neither is good :(

I will need to do more testing to confirm which is which. I will write a part two of this in the next few weeks.