Chopping Static in my Radios

[Rmag]

  On 5/19/2017 at 4:16 AM, Piloto said:

Check the engine ground strap connection at the back of the engine. Without this strap the engine acts as antenna for the magnetos.

José

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It has a strap.

  On 5/19/2017 at 4:56 PM, EricJ said:

It seems pretty clear that it's ignition noise, but it can come from any of the plugs or leads, not just the magnetos.   A loose lead or a damaged lead shield, or even a faulty plug could do this. 

 

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We swapped out all the plugs, and tested all the spark plug wires.

[Piloto]

Rmag when did you started experiencing this noise problem?. Was it after engine/magneto overhaul or it just show up?

José

[Rmag]

I didn't remember it before, but I only flew it a little over 10 hours and then I put it down for half a year so I am not 100% on my recollection.

[Piloto]

Check for broken shield connection at the plug connector. When loosening the connector the lead nut should be kept from rotating to avoid breaking the shield connection. Also check that all the clamps holding the leads should have the plastic insert to keep the shield from making ground contact. Also check any leads for chafing.

Confirm lead shield ground connection at the magneto case by disconnecting the lead from the plug and measuring continuity from the lead nut to the engine case. It should read 0 ohms. When doing this test verify the shield is not grounded by a clamp. Also check center conductor for infinite ohms reading.

José

Edited May 20, 2017 by Piloto

[Rmag]

  On 5/17/2017 at 10:47 PM, Rmag said:

The only thing I haven't done yet and that is where we are heading is to take the magnetos apart to check/replace the condensers.  But a bad condenser you can usually find either L or R mag switch, unless they both are bad and they are both newly overhauled mags.

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Well, It was the right magneto condenser/capacitor.  We replaced it and no more noise.

I was incorrect in what I wrote above; I thought the noise could be isolated by running on the L mag switch.  Apparently such is not the case.  My A&P surmised that even though the R mag is grounded, it is still spinning so the bad capacitor could still send out RF interference.

[carusoam]

Great follow-up on the mag capacitor, Rmag.

A good capacitor probably absorbs electronic noise better than a bad one.

What keeps the bad capacitor working the way it is supposed to?  I would have thought the mag would have failed in a more obvious manner...

Best regards,

-a-

Edited May 23, 2017 by carusoam

[Rmag]

Its kind of ironic that it was the "Rmag" that was the problem.

[Yetti]

How many hours om the magnetos

[Marauder]

  On 5/23/2017 at 6:46 PM, Rmag said:

Its kind of ironic that it was the "Rmag" that was the problem.

Indeed. Just don't change you name to lmag.


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[Rmag]

  On 5/23/2017 at 10:38 PM, Yetti said:

How many hours om the magnetos

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Less than 15 since overhaul. 

[Yetti]

hmmm  There is a way to test the capacitors.   Sometimes you should just do it based on age.

[EricJ]

  On 5/24/2017 at 12:55 AM, Yetti said:

hmmm  There is a way to test the capacitors.   Sometimes you should just do it based on age.

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Absolutely.   Condensers are often electrolytic capacitors which degrade with age, even on a shelf.    Even if a mag rebuilder installs never-used capacitors, they can be bad from shelf life.   I suspect most don't test them before install.

The airplane I'm (still) attempting to buy only had 30 hours on the dual mag since it was rebuilt but it turned out to be bad and had to be sent off again.   I suspect that may have been crappy condensers, but the second rebuilder took care of whatever it was as the power loss was no longer there.

[Rmag]

  On 5/24/2017 at 1:30 AM, EricJ said:

Condensers are often electrolytic capacitors which degrade with age, even on a shelf.    Even if a mag rebuilder installs never-used capacitors, they can be bad from shelf life.  

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The A&P that fixed mine had a capacitor in stock brand new never used, but the date was 2007.  Even when you order a new part, no gauranty how new the date will be. 

[Rmag]

  On 5/23/2017 at 10:45 PM, Marauder said:

Indeed. Just don't change you name to lmag.

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I should have had you knock on wood.  While the right condenser replacement removed the chopping at low RPM, I flew yesterday and at high RPM the chopping noise was there just as bad.  So we replaced the condenser in the left mag today.  On a ground run up to 2400 RPM today, the chopping was gone.

  On 5/24/2017 at 1:30 AM, EricJ said:

Absolutely.   Condensers are often electrolytic capacitors which degrade with age, even on a shelf.    Even if a mag rebuilder installs never-used capacitors, they can be bad from shelf life.   I suspect most don't test them before install.

The airplane I'm (still) attempting to buy only had 30 hours on the dual mag since it was rebuilt but it turned out to be bad and had to be sent off again.   I suspect that may have been crappy condensers, but the second rebuilder took care of whatever it was as the power loss was no longer there.

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The two removed condensers were dated 2000.  So they were 17 years old.  The new ones we put in were dated 2007 and 2016.

[Rmag]

The saga continues.  I'm starting to get frustrated.

Changing the magneto capacitors made the noise go away.  But it slowly came back over my next two flights and now it's as bad as it originally was.

The fact that the noise went away and then came back makes me wonder if the 2007 "new" capacitor degraded while on the shelf for 10 years.  Maybe it worked and then failed?

Anyone know of a shop that has test rigs to energize and leak test bendix mag capacitors near SE PA?  

[takair]

I am thinking you have another issue that is complicating this.  It seems odd that you would get so many bad caps, with symptoms that are so peculiar.  It seems that we would hear about it more often.  Often, with electrical noise, when something makes it go away, but it comes back, you are dealing with a bonding issue that has somehow been manipulated in troubleshooting.  I know you had said you have the ground strap on the engine, but I have seen these attached inappropriately.  In one instance I ran into one the was attached to the engine mount bolt that went through the rubber mount.  It would pick up an adequate ground to read good with an ohm meter, but not adequate for true bonding.  A couple of things come to mind with overhauled mags.  Is it possible that the mating surface has paint on it? (Well...just thought about it, there is a gasket...but get a good bond with the clamp) It just seems like you are not completing a circuit somewhere.  I am also still curious if you have showter of sparks.  I know that it does not normally cause noise like that, but perhaps in some failed condition it sets up a harmonic.  It would be interesting to isolate the wire from the mag....although it would be difficult to start.  Also, I don't know that the entire ignition switch has been ruled out.  They have failed on occasion and they do provide the ground to the p lead.  Can't quite tell you the failure mode, but it is worth considering or ruling out.

I know a couple of EE guys across the field from you who might be willing to help and are quite good at solving odd electrical issues.  PM me if you are interested and I can reach out to them....you likely already know them.

[Rmag]

No shower of sparks. It's an impulse coupling.  Bendix S-1200 mags.  I completely disconnected the P leads and ran it to take out that wiring.  Mag harness was tested with a high tension lead tester and ohm meter. They are not shorted out or degraded.  The noise can still be heard in a unwired handheld radio too.

i'll look again at the bonding strap and the mag housing...

The thing that's killing me is that the noise went away when we initially did the capacitor.  

[takair]

I was just looking at the overhaul manual. There are numerous opportunities within the magneto to have a bad terminal or contact and that may make it look like the capacitor is out of the circuit.  Some of the terminals are simple friction type.  Anyway, if it comes to taking the magneto off again, I would have them look at each terminal to make sure they are clean and tight.  This is a tough one.  Hope you find an answer soon.  As a side note, the handheld can be somewhat misleading, as they tend to be more sensitive to noise and are not part of the same ground circuit as the airframe.  It is a good test, but not always perfect.

[Andy95W]

Do you have anything plugged in or charging from your cigar lighter?  It may make sense to keep looking for causes beyond just the engine.

[N601RX]

One of the coils may be breaking down and arcing between windings internally.  The new caps may have been able to hide it for a flight or so until the arcing got worse. 

[Rmag]

  On 6/3/2017 at 3:56 PM, Andy95W said:

Do you have anything plugged in or charging from your cigar lighter?  It may make sense to keep looking for causes beyond just the engine.

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No

  On 6/3/2017 at 7:38 PM, N601RX said:

One of the coils may be breaking down and arcing between windings internally.  The new caps may have been able to hide it for a flight or so until the arcing got worse. 

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No evidence of arcing between the points when the mag was apart.

[LANCECASPER]

  On 6/3/2017 at 2:37 AM, Rmag said:

The saga continues.  I'm starting to get frustrated.

Changing the magneto capacitors made the noise go away.  But it slowly came back over my next two flights and now it's as bad as it originally was.

The fact that the noise went away and then came back makes me wonder if the 2007 "new" capacitor degraded while on the shelf for 10 years.  Maybe it worked and then failed?

Anyone know of a shop that has test rigs to energize and leak test bendix mag capacitors near SE PA?  

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I'd be tempted to try a "new" capacitor in place of the 2007.

[Yetti]

I think the shelf life of a cap is 10 or 15 years.   I would be more looking for something that was moved and now returned to the same position.  On my plane the right mag has a ground from shield of P Lead to spark plug cap screw.  I would solder up new P leads just to eliminate that part of the equation.

[Rmag]

  On 6/3/2017 at 7:38 PM, N601RX said:

One of the coils may be breaking down and arcing between windings internally.  The new caps may have been able to hide it for a flight or so until the arcing got worse. 

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Would this be noticeable on a mag test?

  On 6/4/2017 at 4:08 AM, LANCECASPER said:

I'd be tempted to try a "new" capacitor in place of the 2007.

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This is where I am going next. 

[Rmag]

  On 6/4/2017 at 1:50 PM, Yetti said:

I think the shelf life of a cap is 10 or 15 years.   I would be more looking for something that was moved and now returned to the same position.  On my plane the right mag has a ground from shield of P Lead to spark plug cap screw.  I would solder up new P leads just to eliminate that part of the equation.

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My noise went from non existent to back again without moving anything in between.