Audio jack testing

TLDR

• Conducted wire-to-wire continuity test on audio jacks (still in progress)

Detail

I’m on a business trip in Taiwan this week so I didn’t have much time doing work on the airplane before the trip. I managed to find a few hours to look into the ground loop issue so I started to conduct wire to wire continuity test on the audio jacks.

In the time I had, I was able to go through about half of wires on the rear passenger audio jacks, and discovered a few issues. The process is not done yet, so I haven’t decided what’s the best course of action. I will continue the testing when I get back home.

Expected behavior

According to Midwest Panel Builders, the audio jack barrel seeks ground through GMA245R.

• When the harness is not connected to GMA245R, everything should be open. ie, barrel should have no ground to the airframe.
• When connected, it should show continuity with airframe.

Test

According to my wire diagram, audio wires connects to GMA245R through HC connector.

So I designed my test to 3 parts:

1. HC disconnected, test continuity between audio jack and HC connector
2. GMA245 disconnected, test continuity between audio jack and GMA245 connectors
3. All connected, test continuity between audio jack and airframe.

All connected

5 out of 8 shows ground. The ones not showing ground are

• Right passenger Mic
• Left passenger Mic
• Left passenger Headset

This is the original state from last week when the whole situation drew my attention.

HC disconnected

No ground to airframe. This is expected, good.

Wire to wire. This is where things get interesting. I discovered 4 pins mismatch according to my wire diagram. See table below

I think HC pin 4 and 5 are swapped, and 7 and 8 are swapped.

I must do more testing here to confirm.

GMA245 disconnected

Haven’t done this part yet. I will revise this section once the testing is done.