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Popping and crackling in audio panel


Denise

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I’ve owned my 1977 Mooney M20J for 26 years.  Put a factory reman engine in it with the two mags this spring and have about 90 hours on the engine.  In the last 10-15 hours I began to get a crackling and popping noise through my audio panel.  It was intermittent at first but now happens on every flight. It only occurs in flight usually at higher MP and RPM.  Not long after I reach cruise, raise the gear and close the cowl flaps it will start.  We can aggravate it in flight and minimize it by touching wires but can’t seem to identify the root cause and therefore forcing it to happen on the ground. 

I’ve isolated each radio and transponder —noise only goes away when the audio panel is off. 

Checked mags and alternator added a filter to alternator as a precaution. 

Anyone have any ideas? Going to swap Garmin 340 audio panel next. 

Engine runs great. Flew the airplane from CA to KFFA this summer. Thankfully this didn’t start until I had returned.  

9F0308B4-14B2-4A33-AFFD-F5C0987F8E7F.jpeg

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It is always worthwhile in cases like this to check ground connections.  First and foremost would be the engine ground straps to the airframe, the alternator ground, and magneto shield grounds.  While you’re poking around the engine compartment, check all visible wires as well.  You’re looking for loose connections.  For the grounds, you’re checking for loose and/or dirty connections.  Since the problems started not long after the engine swap, the engine compartment would be a good place to begin.

Also suspect would be the audio panel grounds, and since that includes your intercom, the intercom ground- which should be a single point.  There should also be a common avionics ground, or definitely not more than a couple of common grounds.

Good luck, keep us posted.

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Welcome aboard Denise...

Your first post wins today’s “where have you been” prize! :)

We have a few members that officially join a few years after they start their Mooney ownership...

With 27 years of Mooney ownership... that in itself is really impressive!

Its not really your first post is it?  The problem statement is really well written and clear... and the pic is standing upright... :)

After all that... Andy did a great job of describing the usual suspects to check regarding noises in the audio system...

We have Greg avionics shop guru around here I like to include in the conversation in case he sees something specific... @Baker Avionics

got any pics from that loooong X-country?


Best regards,

-a-

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Denise, welcome aboard. My wife and I met you at Ken and Beth's hangar at their Christmas party.

Does it vary at all with RPM? The issue I had with a popping/crackling sound was related to a new transponder I installed, but it occurred with or without the engine running and ended up being easy to diagnose. It sounds like you have something else going on, quite possibly an issue with a ground like Andy was mentioning.

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Do you have a noise reduction capacitor?  In our 65C, it was mounted in the engine compartment on the firewall.  When our noise started, it was addressed with a new capacitor.  When a capacitor goes bad, it can often be diagnosed visually if there's a slight bulge in the side and/or end walls.  

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In 16 years of ownership, we've chased several popping/crackling/whining noises.  Looked at alternators, voltage regulators, etc.

In the end, every single one of these gremlins turned out to be a loose ground connection, fixed by tightening or replacing a screw.  It's a pain to look "everywhere" and chase them down, but it's inexpensive/free to look.  So I strongly concur with Andy95W's advice.  Check the grounds first.  If you don't find anything, check again before pursuing other ideas.

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I struggled for weeks with a very similar crackling & popping. It ended up being the rear audio/headphone jack rubbing against the foil insulation behind the wall panel. A little electrical & duct tape fixed it. It may be worth looking at if you have exhausted all other possibilities. 

Edited by Matt_AZ
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When you say you checked the mags, what did you do?  I say this because loose/worn spark plug connections or wiring harness will do that and you mentioned it increased with rpm.  I suggest next time you fly it, do an inflight mag check and listen closely if it goes away or changes with the mags grounded one at a time. Maybe one of the harness wires is old/bad or pulling on a plug wrong after the engine swap.

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On 12/21/2020 at 9:57 PM, Skates97 said:

Denise, welcome aboard. My wife and I met you at Ken and Beth's hangar at their Christmas party.

Does it vary at all with RPM? The issue I had with a popping/crackling sound was related to a new transponder I installed, but it occurred with or without the engine running and ended up being easy to diagnose. It sounds like you have something else going on, quite possibly an issue with a ground like Andy was mentioning.

Yes unfortunately we cannot create the noise on the ground.  Does not have any harmonic to it or appear to be tied to an engine rhythm.  Are you the fella with the D model?  I spent 6 hours with an avionics guy.  And several hours checking loose connections but haven’t found the issue. I will follow Andy’s suggestions and go through the engine again. Thank you.

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On 12/22/2020 at 8:40 PM, Ragsf15e said:

When you say you checked the mags, what did you do?  I say this because loose/worn spark plug connections or wiring harness will do that and you mentioned it increased with rpm.  I suggest next time you fly it, do an inflight mag check and listen closely if it goes away or changes with the mags grounded one at a time. Maybe one of the harness wires is old/bad or pulling on a plug wrong after the engine swap.

I did a mag check early on and no change noted.  Also pulled the alternator circuit breaker and noted no change. Would like to find the smoking gun here. Engine is so clean and all tight. I know it is something but very illusive. 

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On 12/22/2020 at 6:54 AM, neilpilot said:

Do you have a noise reduction capacitor?  In our 65C, it was mounted in the engine compartment on the firewall.  When our noise started, it was addressed with a new capacitor.  When a capacitor goes bad, it can often be diagnosed visually if there's a slight bulge in the side and/or end walls.  

I will check the capacitor.

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On 12/21/2020 at 9:12 PM, Andy95W said:

It is always worthwhile in cases like this to check ground connections.  First and foremost would be the engine ground straps to the airframe, the alternator ground, and magneto shield grounds.  While you’re poking around the engine compartment, check all visible wires as well.  You’re looking for loose connections.  For the grounds, you’re checking for loose and/or dirty connections.  Since the problems started not long after the engine swap, the engine compartment would be a good place to begin.

Also suspect would be the audio panel grounds, and since that includes your intercom, the intercom ground- which should be a single point.  There should also be a common avionics ground, or definitely not more than a couple of common grounds.

Good luck, keep us posted.

It has to be something in the engine.I will go back through the connections using your checklist.  Thank you.

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22 minutes ago, Denise said:

Yes unfortunately we cannot create the noise on the ground.  Does not have any harmonic to it or appear to be tied to an engine rhythm.  Are you the fella with the D model?  I spent 6 hours with an avionics guy.  And several hours checking loose connections but haven’t found the issue. I will follow Andy’s suggestions and go through the engine again. Thank you.

Yep, that's me. Good luck on the search, electrical intermittent stuff can difficult to nail down. 

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Yes unfortunately we cannot create the noise on the ground.  Does not have any harmonic to it or appear to be tied to an engine rhythm.  Are you the fella with the D model?  I spent 6 hours with an avionics guy.  And several hours checking loose connections but haven’t found the issue. I will follow Andy’s suggestions and go through the engine again. Thank you.


In addition to what Byron (jet driven) commented about (the little insulating washers on each headset jack port), make sure the ports themselves are not near anything that could allow them to make contact with anything metallic.

I had a similar issue that only manifested itself at higher power settings. Turns out that when Bruce installed the Spatial Designs interior, the new mounting place for the rear headsets allowed them to contact the foil backed insulation on the sidewalls.
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On 12/21/2020 at 9:17 PM, carusoam said:

Welcome aboard Denise...

Your first post wins today’s “where have you been” prize! :)

We have a few members that officially join a few years after they start their Mooney ownership...

With 27 years of Mooney ownership... that in itself is really impressive!

Its not really your first post is it?  The problem statement is really well written and clear... and the pic is standing upright... :)

After all that... Andy did a great job of describing the usual suspects to check regarding noises in the audio system...

We have Greg avionics shop guru around here I like to include in the conversation in case he sees something specific... @Baker Avionics

got any pics from that loooong X-country?


Best regards,

-a-

Thank you.  I have loads of photos from my trip to KFFA.  Here are just a few.  

6C100A54-69DA-497B-AB99-7778FAEA7905.jpeg

8795A986-B97A-488F-8CA7-BE6C24E2843C.jpeg

9C73B24A-9389-48CB-82D6-84A3F197C787.jpeg

8BC0F3A4-EE6D-4842-87AE-B3FB4F21FC70.jpeg

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3 hours ago, Denise said:

I did a mag check early on and no change noted.  Also pulled the alternator circuit breaker and noted no change. Would like to find the smoking gun here. Engine is so clean and all tight. I know it is something but very illusive. 

Just went through the battery ground, cleaned sanded greased and reattached.  Also removed cowl.  We had cleaned a connector to a P-lead before but this time noticed that a tie wrap forced the wire to have two 90 degree turns at each end.  Some of the insulation missing but the wires appear intact.  We removed the tie wrap so there is less angle.  No static on the test flight.  I have 100 hour coming up soon so I’ll have the p-lead replaced then. Until then I’ll get a few more hours on it and confirm the issue is solved.  Thank you all for your help.  We were scratching our heads in this one.  

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On 12/21/2020 at 4:05 PM, Denise said:

I’ve owned my 1977 Mooney M20J for 26 years.  Put a factory reman engine in it with the two mags this spring and have about 90 hours on the engine.  In the last 10-15 hours I began to get a crackling and popping noise through my audio panel.  It was intermittent at first but now happens on every flight. It only occurs in flight usually at higher MP and RPM.  Not long after I reach cruise, raise the gear and close the cowl flaps it will start.  We can aggravate it in flight and minimize it by touching wires but can’t seem to identify the root cause and therefore forcing it to happen on the ground. 

I’ve isolated each radio and transponder —noise only goes away when the audio panel is off. 

Checked mags and alternator added a filter to alternator as a precaution. 

Anyone have any ideas? Going to swap Garmin 340 audio panel next. 

Engine runs great. Flew the airplane from CA to KFFA this summer. Thankfully this didn’t start until I had returned.  

9F0308B4-14B2-4A33-AFFD-F5C0987F8E7F.jpeg

By chance have you looked at your headset and mic jacks to be certain they are isolated from the panel and/or ground?  That can induce issues as well as if you have a "music jack" to plug and iPad or phone into.  If they are not isolated via insulation washers, it is most likely a culprit. Other than that, the shielding for the audio panel could have came loose and be certain to check the JPI you  have as well as I believe that there is an audio line going from there to the Audio Panel.  You said you "checked the mags"? In what manner?  Be certain that the P Lead going to the actual mags has a shield over the wire and that shield is in fact grounded as well.  It could induce issues as well.  

Because it is "popping" is seems like a mag wiring issue.  Not a mag issue, a mag wiring issue.  Also ensure that the strobe lights are not on as well to see if it could be coming from the strobes as well.  I will check back to see what you find. If yo need more direct advice, either call or email me directly.  We are here to help. 

 

P.S.- Anthony @carusoam check out the title on my profile to the left here.  Oh yeah baby!!!!!!

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  • 2 weeks later...

Did you find the problem?  And sorry if someone asked this, I didn't see it...

If you grab the headset connector and twist it back and forth a bit, do you hear the crackling?  The connectors can build up oxidation and dirt and you may hear the crackling from the vibration when the plane is running or by your movement if you tug a little on the cable.

If this turns out to be the issue, give all the connectors a few twists back and forth until it clears up and then a few extras for good measure.  You don't need twist really hard, just twist back and forth somewhat quickly until the crackling goes away.  Do the same amount with the mic connectors.

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