GMA 345 Audio Panel issue

Greg Ellis

Greg Ellis

Filing Flight Plan
Joined
Feb 9, 2021
Messages
22
Location
Fort Worth, Texas
Display Name
Display name:
Greg
I am having an issue with my audio panel and only through Com 2. Instrument list: GMA 345, GTX 345, Garmin 530W, Garmin GNC 300XL, G5 HSI, JPI EDM 900.

There is a recurring noise through the Com 2 on the audio panel. It is the one the GNC300 goes through. Volume does not affect it. I have changed out the GNC 300XL for another one and nothing changed. I pull all circuit breakers except for the GNC 300XL and the audio panel and the noise is still there. It happens whether the engine is running or not. I can be sitting in my hangar with just the master switch and avionics master on and nothing else except for the audio panel and GNC 300XL and the noise is there. I have checked the antenna, the coax, my avionics shop is stumped and they put in an inline noise suppressor and still no change. They have checked all of the grounds and shielding. I am left with the possibility of the audio panel itself being the problem. Even when I fly and am away from the airport this noise continues so I don't believe it is anything at the airport. And of course, when you turn off the GNC300XL and there is no input to the audio panel the noise goes away so it is not just something coming from the audio panel but maybe the audio panel is having an issue when sound is coming through the #2 Com.

I have attached a link to the audio noise. It is actually a video on Youtube but it is just for the audio so I could send it out to see if I can get any help. Right now my avionics shop is stumped and so am I.
 
Greg Ellis said:
I pull all circuit breakers
Click to expand...
Do you pull only the avionics CBs or all the CBs in the aircraft?
Greg Ellis said:
I have checked the antenna, the coax,
Click to expand...
Have you tried leaving the the COM 2 antenna coaxes disconnected on both ends during your test?

Is the connector for the audio panel properly seated?

Do you hear it at all headset locations also?
 
Bell206 said:
Do you pull only the avionics CBs or all the CBs in the aircraft?

I pull out all of the circuit breakers except for the one for the audio panel and the GNC 300XL.

Have you tried leaving the the COM 2 antenna coaxes disconnected on both ends during your test?

I have not tried this. I only disconnected from back of the GNC 300XL not from the antenna.

Is the connector for the audio panel properly seated?

So far my avionics shop says it looks fine.

Do you hear it at all headset locations also?

It can be heard on all 4 headset locations.
Click to expand...

Thank you for your response.
 
What model aircraft?
Are there any battery direct systems on the panel like a clock?
Does your audio panel have bluetooth option?

My WAG at the moment is a shielding issue somewhere.
 
Bell206 said:
What model aircraft?
Are there any battery direct systems on the panel like a clock?
Does your audio panel have bluetooth option?

My WAG at the moment is a shielding issue somewhere.
Click to expand...

It is a 1963 Mooney M20C. The audio panel does have bluetooth. I don't have it on or trying to pair with anything. The clock is a Davtron. But the noise continues even when I pull its circuit breaker. I think you may be right about the shielding issue. Just trying to get my avionics shop to look at it again. They are quite busy. Thank you for your responses. I appreciate the guidance.
 
Greg Ellis said:
But the noise continues even when I pull its circuit breaker.
Click to expand...
I'm thinking it maybe caused by something up stream of the CBs. Since you've pulled CBs and swapped the 300 that "leaves" the wiring and audio panel as the unknown. The only schematics I can dig up are for a 20J which shows a few power system items that could create noise, but I don't know if they apply to your 20C. Perhaps try to bypass the normal power paths and apply clean voltage direct to the avionic buss powering the 300 and 345 audio. That would require disconnecting a few things and I'm sure none of them are easy to get to. But it may be easier than wringing out every shielded wire. Might also pull the audio panel and look at the back plug pins with a glass to see if any are unseated or bent. Can your shop bench check the audio panel? If not, maybe see if they can recommend a shop while they work to fit you in. If the audio panel passes the bench check should narrow the search to just the wires with a heavy point on the "should.";)
 
Bell206 said:
I'm thinking it maybe caused by something up stream of the CBs. Since you've pulled CBs and swapped the 300 that "leaves" the wiring and audio panel as the unknown. The only schematics I can dig up are for a 20J which shows a few power system items that could create noise, but I don't know if they apply to your 20C. Perhaps try to bypass the normal power paths and apply clean voltage direct to the avionic buss powering the 300 and 345 audio. That would require disconnecting a few things and I'm sure none of them are easy to get to. But it may be easier than wringing out every shielded wire. Might also pull the audio panel and look at the back plug pins with a glass to see if any are unseated or bent. Can your shop bench check the audio panel? If not, maybe see if they can recommend a shop while they work to fit you in. If the audio panel passes the bench check should narrow the search to just the wires with a heavy point on the "should.";)
Click to expand...

Thanks for the information. I believe they can bench test it. I have been in their shop and they have an area with testing equipment, etc... They are able to work me in tomorrow afternoon so hopefully I will get answers then. Thanks again for your responses.
 
Greg Ellis said:
Thanks for the information. I believe they can bench test it. I have been in their shop and they have an area with testing equipment, etc... They are able to work me in tomorrow afternoon so hopefully I will get answers then. Thanks again for your responses.
Click to expand...
Almost sounds like morse code. Any chance one of your NAV is "leaking"?
 
Greg Ellis said:
Thanks for the response. They are actually going to check that when they can get to it next week. I appreciate the response.
Click to expand...
Please let us know what they found. Thanks.
 
The absolute quickest check would be to borrow a known good GMA and slide it into your panel. If the problem goes away, it's your unit. If not, it's ship-side.

I have found in rare cases that shops or weekend troubleshooters overtightened the unit in the tray. Since the mechanism threads into the center of the back plate, over-tightening can cause the plate to bend and actually cause the connectors to move AWAY from the back of the unit itself.

Keep us posted
 
You must log in or register to reply here.
Back
Top