2000 ovation comms/radio/electrical issue

[Subternal]

Morning forum, 

Was hoping to get some feedback or suggestions of a nagging electrical/comms issue I'm going through. I guess first I'll tell you about the plane:

-2000 ovation 2

- Garmin 430/530 non-waas. 

-PMA7000b audio

-KFC225 

 

So here's my nagging issue: infrequently but consistently the radio transmit is engaged/active/open. I'm trying to use my words carefully to explain the problem but basically I've already replaced both push to talk buttons and verify the old ones were not the issue. The active transmit seems to happen randomly, at least to me. I will go several flight hours with no issue and then randomly the transmit will not close. The push to talk button is not stuck. My PMA 7000 has a com3 option that I usually select to not have an open mic. As I said before I've already replaced both PTT buttons with no change. Even if I switch off my PMA 7000 while the problem is happening it simply reverts to com1 in my gns 530. It will remain Open Mic until I switch on my PMA 7000 and select comm 3. I've noticed the issue seems to happen more on hot days I've also made a few trips to Florida where the problem seems to be more frequent. I've also noticed that there seems to be quite a bit of heavy static or crackling on the comms line before the issue happens. Before I start pulling out wires I'm just curious if anyone else has run into issues like this or can help diagnose or troubleshoot or just advise in general, thanks again for any help.

[WilliamR]

Have you had your maintainer check the wire from the PTT?

What are their ideas besides changing the PTT switch? 

Sometimes, over time, those wires from the PTT can develop hairline cracks in the insulation which then grounds to the closest metal surface like a yoke shaft which acts like a PTT being pushed (hot mike). That's usually the next easiest place to have your avionics mechanic look.

William

 

 

[Yetti]

So the PTT works by closing to ground.   so basically you are getting a short to ground.   The wire from the PPT switch to the COM panel has an issue.   I would first check to see that there is not a strand of wire shorting at the back of the COMM.   also check for short where the wire comes out of the back of the yoke tubes.

If you pull the panel and get to the comm connector you could put a VOM on the PTT pin in the connector then wiggle each PTT wire and see if you get a reading.

Report back your findings.

[Ragsf15e]

I might also suggest pulling the pma7000, cleaning the connections as much as possible on both the unit and rack, then re-racking it.

[Yetti]

13 minutes ago, Ragsf15e said:

I might also suggest pulling the pma7000, cleaning the connections as much as possible on both the unit and rack, then re-racking it.

The same can be accomplished by pulling out and putting in several times over.    That would correct an absence of connection.    OP is dealing with wrong connection at the wrong time.

[Subternal]

1 hour ago, Yetti said:

The same can be accomplished by pulling out and putting in several times over.    That would correct an absence of connection.    OP is dealing with wrong connection at the wrong time.

Thank you for your input. And I will have to take a serious look at the PTT to com run of the wire. 

 

On a second note I recently had the PMA 7000 upgraded to the Bluetooth model, but had the issue before and after the update/upgrade. I only mention because I think that kinda ruled out the audio panel.

 

Additionally, I put this post out to ask for more detail on the COM hardware in the GNS530/430; could there be a momentary short within the actual box? I accept that the issue is probably the more simpler one. (Ie: prob a short In the wire, but I feel like I gotta ask.)

Edited August 22 by Subternal

[GeeBee]

I've solved a lot of comm issues by cleaning the ground wire off the battery. Both ends.

[MatthiasArnold]

14 hours ago, WilliamR said:

Have you had your maintainer check the wire from the PTT?

What are their ideas besides changing the PTT switch? 

Sometimes, over time, those wires from the PTT can develop hairline cracks in the insulation which then grounds to the closest metal surface like a yoke shaft which acts like a PTT being pushed (hot mike). That's usually the next easiest place to have your avionics mechanic look.

William

Exactly this was the root cause on a rented PA28, when I blocked out ATC communications in busy Düsseldorf control zone for a while until the PTT stuck functionally of the GNS430 ended the TX. 
I entered 7600 on the transponder and communicated wirh ATC via squawk ident button (answering their questions in a yes/no fashion). 
On the way back to the home base I knocked against the yoke shaft from different directions, heard „cracking“ noise in the headset (caused by the PTT wire electrically disengaging from the grounded yoke shaft) and finally brought the wire back into a position, that I was able to transmit again. 
One FI of the flight school/rental told me afterwards  „we have had this problem since years, without any idea of the root cause“. 
BTW: I received no discount for this rental flight…

Matthias
 

[McMooney]

reseat the audio panel, worked for me.

[Subternal]

4 hours ago, McMooney said:

reseat the audio panel, worked for me.

Yup, tried that several times. Also cleaned the contacts I'm the back of the audio panel while it was out. No change. But thanks for the heads up

[Mark89114]

I had the same problem, occurred on both PTT and both COM's and even a dave clark portable PTT.  I replaced the PTT's, had the intercom unit sent back to PS as they led me to believe it was sticky relay in unit.  They went through it and only replaced a few diodes, but they didn't find anything wrong with relays.  Problem hasn't occurred again so I legitimately don't know if anything I did intentionally fixed it, but the simple act of removing and resetting it might have been all it needed.  

[Yetti]

19 hours ago, Subternal said:

Thank you for your input. And I will have to take a serious look at the PTT to com run of the wire. 

 

On a second note I recently had the PMA 7000 upgraded to the Bluetooth model, but had the issue before and after the update/upgrade. I only mention because I think that kinda ruled out the audio panel.

 

Additionally, I put this post out to ask for more detail on the COM hardware in the GNS530/430; could there be a momentary short within the actual box? I accept that the issue is probably the more simpler one. (Ie: prob a short In the wire, but I feel like I gotta ask.)

Probably not, but possibly.   The PTT circuit in the PMA7000 is a dedicated circuit, then the 7000 closes the PTT circuit in the GNS. Which is another circuit.    So the way to tell would be if the XMT light only comes on in the GNS.    The other way is do you hear the side tone in your headset?   If so the PTT in the comm panel is coming on, not just the GNS.    Could the PTT in the GNS fire the PTT in the 7000.  Highly doubtful.

[Subternal]

1 hour ago, Yetti said:

Probably not, but possibly.   The PTT circuit in the PMA7000 is a dedicated circuit, then the 7000 closes the PTT circuit in the GNS. Which is another circuit.    So the way to tell would be if the XMT light only comes on in the GNS.    The other way is do you hear the side tone in your headset?   If so the PTT in the comm panel is coming on, not just the GNS.    Could the PTT in the GNS fire the PTT in the 7000.  Highly doubtful.

Helpful detail. But no, when the transmit is stuck both the audio and gns illuminate.

Another thing came to mind, this may be a dumb question but if it is the PTT on the pilot side that is stuck is there a way to tell using copilot or pilot mic which side it is? More clearly, if I use the pilot side PTT button is the only Mic that is able to transmit on the pilot side or is both the pilot and the co-pilot mic an open mic?

[MikeOH]

8 minutes ago, Subternal said:

Helpful detail. But no, when the transmit is stuck both the audio and gns illuminate.

Another thing came to mind, this may be a dumb question but if it is the PTT on the pilot side that is stuck is there a way to tell using copilot or pilot mic which side it is? More clearly, if I use the pilot side PTT button is the only Mic that is able to transmit on the pilot side or is both the pilot and the co-pilot mic an open mic?

Can you obtain schematics that can help with how your setup is actually wired?  If there are separate PTT wires from pilot/co-pilot PTTs I'd try to de-pin the pilot PTT at the audio panel and see if the problem goes away (fly using the co-pilot mic).  That would isolate the short/problem to the wiring from the pilot PTT to the audio panel.

[Yetti]

24 minutes ago, Subternal said:

Helpful detail. But no, when the transmit is stuck both the audio and gns illuminate.

Another thing came to mind, this may be a dumb question but if it is the PTT on the pilot side that is stuck is there a way to tell using copilot or pilot mic which side it is? More clearly, if I use the pilot side PTT button is the only Mic that is able to transmit on the pilot side or is both the pilot and the co-pilot mic an open mic?

A bit more clarity.  The PMA 7000 has a pin for the pilot and one for the copilot.    This allows for the ability to pilot and copilot to talk on different freqs.   Wiring diagram is here.  So if you set it up to the do the dual coms, you could see which side shorts.    https://www.ps-engineering.com/assets/docs/PMA7000BT_IM.pdf