Feedback and crackling in intercom on power up

[jlbpropilot]

Im trying to troubleshoot an audio issue. When I power up my skyview screen I get lots of noise in my intercom right about the time the Dynon emblem fades away and the self test starts up. The noise continues while the screen is powered but not as noticeable. This problem happens even with the comm and transponder unpowered so I believe the problem is between the screen and the intercom. Presently have the audio connection made between the L audio, R audio, Ground, and Dim using a 4 conductor shielded wire. The shield is not grounded on either end of the run. Any suggestions? Thanks

 

[Eric_Greenwell]

Have you tried a different headset? I had a similar problem which turned out to be a headset going bad. The headset's most noticeable symptom was, intermittently, I did not hear my voice in the headset when I spoke. An identical headset worked fine all the time.

 

[Raymo]

The shield is not grounded on either end of the run. Any suggestions? Thanks

This is likely your problem. Shielding in this area requires grounding at one end (but not both). The ground allows noise to be dissipated.

You should see the shield grounding in the SV installation manual.

 

[jlbpropilot]

I have tried a different headset. Noise only audible when the sky view display is powered up. Im assuming it is probably a grounding issue. In the diagram it shows the wires that run between the intercom and display as only twisted wire and doesn't indicate it should be grounded anywhere. I had picked up somewhere that it should be shielded so that is what i used. Think the shielding should be grounded on either the intercom or screen side? Thanks for the replies

 

[dynonsupport]

Given you say the noise shows up the most when the screen dims, this is almost for sure to be an insufficient ground on the SkyView screen. Dimming in SkyView is actually the screen pulsing on/off very quickly, and this changes the current on the ground wire. If the ground isn't good enough, this current change causes a voltage change which your audio panel "hears".

The quick check for this? A very large ground wire between the case of SkyView and the case of your intercom. You can just hold the wire against both cases to test it. If this helps, then you can look deeper at the root cause. You don't have to keep booting the screen, if it is a dimming issue, you can manually dim the screen and just leave it dimmed as you test the grounding.

This most often happens on non-metal panels. Metal panels tend to ground everything together really well. Sometimes paint interferes with this though.

 

[jlbpropilot]

Still having issues. There must be constant noise coming from my screens that keeps my music input on the intercom muted 90% of the time. I have tried the suggestions above with no luck. If I remove the 3 wires (audio L, audio R, and GRD) that connect the sky view screen directly to the intercom I have no issues with it muting my music input. Obviously at this point I don't get any audio from my screen either. The screen is grounded to a tab on my 4130 fuselage frame by the panel. The intercom, transponder, and comm radio grounds are all crimped on the same ring terminal and grounded to the same spot as the ships battery which is behind the pilots seat. Having the Comm and transponder on do not seem to have any ill effect on the intercom. If I understand the manual correctly pin #30 from the display connects directly to pin #20 on the intercom. Any other help would be greatly appreciated. The easy fix would be to just connect the audio portion and enjoy my music