Avionics Gremlin

[chriscalandro]

What else is that unit wired to

[Greg Ellis]

2 minutes ago, Baker Avionics said:

Is your GNC300 the number 1 radio or number 2?

1.  

It is the #2 radio on Comm 2.

[Baker Avionics]

My questions are, what other Avionics do you have, but if you pulled all of the CB for everything else, it is a little weird. 

[Greg Ellis]

Just now, chriscalandro said:

What else is that unit wired to

Meaning the audio panel?  The GMA 345 is only wired to a Garmin GNS 530W on Comm 1 and a GNC300XL on Comm 2.  No other radios or Nav units.

[Greg Ellis]

Just now, Baker Avionics said:

My questions are, what other Avionics do you have, but if you pulled all of the CB for everything else, it is a little weird. 

So, I have a 530W, the 300XL, a G5, the GMA 345, a GTX 345 transponder, and a JPI 900.  No autopilot, no other nav or comm radios.

[Greg Ellis]

There is also a GAD29.

[chriscalandro]

51 minutes ago, Greg Ellis said:

Meaning the audio panel?  The GMA 345 is only wired to a Garmin GNS 530W on Comm 1 and a GNC300XL on Comm 2.  No other radios or Nav units.

well it sounds a lot like crosstalk between a data bus, either serial, arinc, or other into the audio circuit.  It could be internal, it could be a wire, it could be a large number of things.

 

Are they standard density pins on the back of that unit?  Should be easy enough to troubleshoot by pulling some pins that aren't power related or audio panel related and see what you get.

[Greg Ellis]

8 minutes ago, chriscalandro said:

well it sounds a lot like crosstalk between a data bus, either serial, arinc, or other into the audio circuit.  It could be internal, it could be a wire, it could be a large number of things.

 

Are they standard density pins on the back of that unit?  Should be easy enough to troubleshoot by pulling some pins that aren't power related or audio panel related and see what you get.

Thanks for the information and I will pass this along to the avionics guys working on it.  Not sure about the pins on the unit.  

[Baker Avionics]

I would look at the shielding or the shield ground going to the same ground as the power. whether you look at the GNC300 or the Audio Panel.  It seems like that to me.  

[MikeOH]

At this point, I would pull the GNC300XL out of the panel and run it on the bench with an external power supply with only a speaker hooked up; no antenna or anything else but the speaker.  That would prove if the GNC is the source, or if it is external interference.

[MikeOH]

Other random thoughts...

Did this problem just start, or is this a new install problem?  (Sorry, if that's been covered)

Does this happen everywhere?  As in, at other airports, in the air, or just at your home airport?

The fact that the #1 comm doesn't have the issue suggests (but does NOT prove) that the problem is either poor shielding (as Greg Baker suggests), or that it is internal to the unit itself.

[Greg Ellis]

9 hours ago, MikeOH said:

At this point, I would pull the GNC300XL out of the panel and run it on the bench with an external power supply with only a speaker hooked up; no antenna or anything else but the speaker.  That would prove if the GNC is the source, or if it is external interference.

That's a great idea.  I will pass this along.  Thanks.

[Greg Ellis]

11 hours ago, Baker Avionics said:

I would look at the shielding or the shield ground going to the same ground as the power. whether you look at the GNC300 or the Audio Panel.  It seems like that to me.  

I passed the info along regarding the shielding.  I appreciate your help with this.

[Greg Ellis]

8 hours ago, MikeOH said:

Other random thoughts...

Did this problem just start, or is this a new install problem?  (Sorry, if that's been covered)

Does this happen everywhere?  As in, at other airports, in the air, or just at your home airport?

The fact that the #1 comm doesn't have the issue suggests (but does NOT prove) that the problem is either poor shielding (as Greg Baker suggests), or that it is internal to the unit itself.

It is not a new problem and has been happening for a while.  It does occur everywhere.  I have switched the GNC300XL out with another GNC300 that I have and it still happens.  The shop has a GNC300 that they were going to put in an try as well.  Thanks for your response.  I am passing along all of this information to the shop.  I don't think they have had a chance to look at it.  They have been very busy.  They were going to try to get to it this week but I leave tomorrow for the Mooney Caravan clinic and was hoping they would solve it before I leave.  

[Greg Ellis]

Some of you are aware and have provided excellent advice on how to solve this ongoing issue of the repetitive noise I have through my #2 comm.  To review, my avionics shop checked all the wiring again, they installed a different #2 GNC 300XL to see if it was my GNC 300XL.  They took out my GMA 345 and put a new one in to see if it was my audio panel, they checked all coax cables, all grounds, even went back and forth with Garmin multiple times. Nothing worked.  I was getting tired of not having my airplane around when I wanted it and not having quality radios that were quiet.

So, getting tired of this I figured, hey, money can usually solve airplane issues so I threw a little, well a lot more money at the problem.  I had them remove the GNC 300XL and all its components like the tray and wiring etc...  I had them install a Garmin GNC 355.  Viola....all noise is gone, everything is quiet and the radio sounds great.

So I wish I had something really cool to report but according to Garmin, there was something about the actual tray that the GNC 300XL sits in and the connectors at the back that was causing the issue and that is why a different GNC 300XL did not solve the problem.  It took a more modern GPS install to solve the problem.

I am just happy that I no longer have to listen to that awful noise on the #2 radio and I can now start putting money towards the GFC500 Autopilot!!!!

Thanks for any and all advice from the group.

[carusoam]

Fantastic follow-up Greg!

Best regards,

-a-