Avionics Gremlin

[Greg Ellis]

Calling all avionics experts….
So, I have been having great difficulty tracking down an issue with my avionics.  I have a 530W, a GNC 300XL, a GMA 345 audio panel, a G5, JPI, and GTX 345 transponder.  The issue is with the GNC 300XL.  I am posting this video which is really just for the audio.  You can hear the noise that is being made.  The 530 is nice and quiet.  This is coming from the GNC 300.  I have tried pulling all circuit breakers to eliminate any other instruments causing interference.  Nothing changes.  I have removed the comm coax from the back of the GNC 300 and the noise continues.  It is not affected by volume control.  You can adjust the volume and the noise stays at the same level.  This is recorded from the over head speaker but the noise can be heard in the headsets as well so it is not the speaker.  I have tried a different GNC 300 and the noise continues.
I am out of ideas.  My avionics shop is not sure what’s happening but they are looking at possibly putting in an in line noise suppressor or something to that effect.

Any ideas?

 

[OR75]

almost like an ident sound 

did you check if it sounds different with a different Nav frequency ?

 

[jlunseth]

One, check to make sure you have not hit the squelch button. There should be some means showing "SQ" if you have. Easy to do by mistake and easy to miss. Two, many gremlins are caused by plug-in chargers and other non-panel mounted devices. Shut them off one by one to see if things change. Also try disconnecting any bluetooth pairings. Almost sounds like it is receiving a periodic broadcast of some kind like the transponder's burst.

[Greg Ellis]

54 minutes ago, OR75 said:

almost like an ident sound 

did you check if it sounds different with a different Nav frequency ?

 

Frequency doesn’t seem to matter.  Thank you for the response.

[Greg Ellis]

2 minutes ago, jlunseth said:

One, check to make sure you have not hit the squelch button. There should be some means showing "SQ" if you have. Easy to do by mistake and easy to miss. Two, many gremlins are caused by plug-in chargers and other non-panel mounted devices. Shut them off one by one to see if things change. Also try disconnecting any bluetooth pairings. Almost sounds like it is receiving a periodic broadcast of some kind like the transponder's burst.

Thanks for the response.  I methodically unplugged all devices.  Pulled the circuit breaker on the transponder, the squelch is not on, I checked that as well.  Even turned my cell phone off as well as the Bluetooth part of it.  I thought about the periodic broadcast as well just because of the way it sounds.  This is the problem.  Nothing I do seems to even alter it let alone fix it.

[PT20J]

If it were noise getting into the receiver or an open squelch the volume should change with the volume control. If it just started doing this it is probably a failure of the unit. If it has always done it I'd check all the connections, especially the grounds.

[EricJ]

Is that the only thing you ever get out of the unit?  i.e., does it generate normal audio (or at least noisy audio) when receiving?

If I understand correctly the noise is there even if the only things that are on are the GNC300 and the audio panel?   If so does the noise go away when the GNC300 is turned off or its breaker pulled, but the audio panel left on?    That would isolate that the GNC300 is the source and it's not getting picked up in the audio panel or between the GNC300 and the audio panel.

Are there any USB power jacks on anywhere?    Nothing else on the airplane is powered, e.g., strobes, etc.?

 

[McMooney]

4 hours ago, Greg Ellis said:

Calling all avionics experts….
So, I have been having great difficulty tracking down an issue with my avionics.  I have a 530W, a GNC 300XL, a GMA 345 audio panel, a G5, JPI, and GTX 345 transponder.  The issue is with the GNC 300XL.  I am posting this video which is really just for the audio.  You can hear the noise that is being made.  The 530 is nice and quiet.  This is coming from the GNC 300.  I have tried pulling all circuit breakers to eliminate any other instruments causing interference.  Nothing changes.  I have removed the comm coax from the back of the GNC 300 and the noise continues.  It is not affected by volume control.  You can adjust the volume and the noise stays at the same level.  This is recorded from the over head speaker but the noise can be heard in the headsets as well so it is not the speaker.  I have tried a different GNC 300 and the noise continues.
I am out of ideas.  My avionics shop is not sure what’s happening but they are looking at possibly putting in an in line noise suppressor or something to that effect.

Any ideas?

 

I had the same issue Wednesday flying from KUTA to KDWH. 

was thinking it was the mags/surefly/alternator/VRr making the noise as it continued with everything except for the audio panel off.   

Edited May 8, 2021 by McMooney

[Greg Ellis]

4 hours ago, EricJ said:

Is that the only thing you ever get out of the unit?  i.e., does it generate normal audio (or at least noisy audio) when receiving?

If I understand correctly the noise is there even if the only things that are on are the GNC300 and the audio panel?   If so does the noise go away when the GNC300 is turned off or its breaker pulled, but the audio panel left on?    That would isolate that the GNC300 is the source and it's not getting picked up in the audio panel or between the GNC300 and the audio panel.

Are there any USB power jacks on anywhere?    Nothing else on the airplane is powered, e.g., strobes, etc.?

 

Thanks for the response.  The unit does generate normal audio.  I use it to talk to ground and get ATIS.  Yes, the noise is there with only the audio panel and the unit on.  The noise goes away when the unit is off or breaker pulled.  All lights are off and no USB power jacks except for the one built in to the audio panel.  It happens with this unit as well as a second GNC 300 that I have.  So either both units are bad or it is something else.  My avionics shop has a GNC 300 on their shelf.  I will get them to swap it with mine and see what happens.  Could be two units are bad I suppose.

[Greg Ellis]

2 hours ago, McMooney said:

I had the same issue Wednesday flying from KUTA to KDWH. 

was thinking it was the mags/surefly/alternator/VRr making the noise as it continued with everything except for the audio panel off.   

Thanks for the response.  This only happens with the GNC 300.  The 530 is as quiet as a church mouse.  When I recorded this audio the airplane was shut down, I was in my hangar.  The only thing on was the master switch, the avionics master and the GNC 300 and the GMA 345 audio panel.

[Greg Ellis]

4 hours ago, PT20J said:

If it were noise getting into the receiver or an open squelch the volume should change with the volume control. If it just started doing this it is probably a failure of the unit. If it has always done it I'd check all the connections, especially the grounds.

Thanks for your response.  They are going to check the grounds as well hopefully early next week before The Mooney formation clinic next weekend.

[carusoam]

Did sound like a repeated signal...

Grab a few mechanics at the airport... play a Game of guess that tune... 

Somebody might recognize it’s source...

Best regards,

-a-

[Greg Ellis]

Just now, carusoam said:

Did sound like a repeated signal...

Grab a few mechanics at the airport... play a Game of guess that tune... 

Somebody might recognize it’s source...

Best regards,

-a-

Two A&P/IA’s and the avionics guy who installed everything and is very experienced are scratching their heads….

[carusoam]

when looking for experience like this....

Let’s ask Greg @Baker Avionics

He may have heard something like this...

Best regards,

-a-

[Greg Ellis]

9 minutes ago, carusoam said:

when looking for experience like this....

Let’s ask Greg @Baker Avionics

He may have heard something like this...

Best regards,

-a-

Thanks for reaching out to him for me.

[Bob Weber]

That sounds like a data burst to me.. A quick peak of a GMA 345 manual shows 17 and 18 of P2 as an RS 232 in and out, anything tied to those pins?

Probably a poke in the dark but you never know.

[Greg Ellis]

10 hours ago, Bob Weber said:

That sounds like a data burst to me.. A quick peak of a GMA 345 manual shows 17 and 18 of P2 as an RS 232 in and out, anything tied to those pins?

Probably a poke in the dark but you never know.

Thanks for the response.  I will pass this along to my avionics guys and see what they say.

[N201MKTurbo]

Turn off your cell phone.

[Greg Ellis]

Just now, N201MKTurbo said:

Turn off your cell phone.

With the cell phone in Airplane Mode it still happens.  With the cell phone in my truck it still happens.  Only occurs on Comm 2 not on Comm 1.  Thank you for the response.

[Baker Avionics]

Personally, I would look to be certain the Audio lines going to the Audio Panel from the GNC is shielded and the shield is grounded correctly.  It seems to me that the shield is either loose or not even there.  Further, the Squelch sounds like it is set low on that as well, as mentioned before.  Further, do yo have an entertainment jack installed? You need to be certain that the music/entertainment jack is isolated from ground because it too can cause issues like this.  Other than that, I would have to ask if there is a RX or a TX light showing when this happens.  

[Greg Ellis]

7 minutes ago, Baker Avionics said:

Personally, I would look to be certain the Audio lines going to the Audio Panel from the GNC is shielded and the shield is grounded correctly.  It seems to me that the shield is either loose or not even there.  Further, the Squelch sounds like it is set low on that as well, as mentioned before.  Further, do yo have an entertainment jack installed? You need to be certain that the music/entertainment jack is isolated from ground because it too can cause issues like this.  Other than that, I would have to ask if there is a RX or a TX light showing when this happens.  

Thanks for the information and I will pass it along.  There is no RX or TX light showing when this happens.  The audio actually still functions fine, I can hear the ATIS for instance but this is in the background and is a real annoyance.  The squelch is not on because when I push the squelch button you can tell it is on.  It is very much different and can hear it.  The only music/entertainment thing installed is what comes on the GMA 345 so I can have them check that as well.  Thank you so much for responding.  If you weren't in Oregon I would bring the plane to you. 

[Greg Ellis]

12 hours ago, Bob Weber said:

That sounds like a data burst to me.. A quick peak of a GMA 345 manual shows 17 and 18 of P2 as an RS 232 in and out, anything tied to those pins?

Probably a poke in the dark but you never know.

Avionics guy said that nothing is tied to those pins.

[Baker Avionics]

Just now, Greg Ellis said:

Thanks for the information and I will pass it along.  There is no RX or TX light showing when this happens.  The audio actually still functions fine, I can hear the ATIS for instance but this is in the background and is a real annoyance.  The squelch is not on because when I push the squelch button you can tell it is on.  It is very much different and can hear it.  The only music/entertainment thing installed is what comes on the GMA 345 so I can have them check that as well.  Thank you so much for responding.  If you weren't in Oregon I would bring the plane to you. 

Does it happen all of the time (whether on external power) or only when the engines are running?  

[Greg Ellis]

Just now, Baker Avionics said:

Does it happen all of the time (whether on external power) or only when the engines are running?  

With and without engines running.  Happens all the time.  The recording of the noise was with the airplane in the hangar and the master switch and avionics master on, no engine running.  I pulled all circuit breakers except for the GNC 300 and Audio panel and it still happens.

[Baker Avionics]

Is your GNC300 the number 1 radio or number 2?

1.