Fry Posted May 17, 2020 Report Share Posted May 17, 2020 (edited) A question to the collected cloud intelligence of this forum: Radio noise on the "L" or "BOTH" magnetos in a 1995 Mooney M20J MSE. No noise when on "R". What's your best guess to look for or do? Tnanks for any hints, Fry Edited May 17, 2020 by Fry Quote Link to comment Share on other sites More sharing options...
tmo Posted May 17, 2020 Report Share Posted May 17, 2020 Any capacitors in the magneto circuit? In cars they are (were...) sometimes used to quieten down the coils. Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 17, 2020 Report Share Posted May 17, 2020 There are capacitors in magnetos as part of the OH package... Check the number of hours on the mags since their last OH... 500hrs is a common OH period... for convenience... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Fry Posted May 17, 2020 Author Report Share Posted May 17, 2020 Magnetos were overhauled (or exchanged?) about 120 hours ago, which was in November 2017 with a former owner of the aircraft. Is this commonly solved by a capacitor, or might it be a shielding issue? Why the difference between R and L? Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 17, 2020 Report Share Posted May 17, 2020 Not a common problem at all... See if the capacitor was actually changed out during the OH... Electrical noises are often capacitor related... they filter out noises... when they don’t... they probably stop working as designed... Parts list related to the OH or work order number and a phone call might help with the knowledge gathering... Often mags get shipped to an OH company to take care of the task... not usually locally rebuilt... The most common electrical noise comes from diodes dying in the alternator... unfortunately, this doesn’t change with the ignition switch... Some Mooneys get a noise suppressing filter.... not sure how the ignition switch could be wired to this giant capacitor.... So... keep all options open... nothing stands out as the smoking gun.... PP thoughts only not a mechanic.... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
tmo Posted May 17, 2020 Report Share Posted May 17, 2020 I think it could also be a grounding issue, an out of spec capacitor, or probably many other reasons. Apologies for the possibly assinine question but you are sure you have separate magnetos, not a dual mag, right? But a ground issue would likely also cause issues during a mag check, hence my initial guess of "capacitor". 1 Quote Link to comment Share on other sites More sharing options...
N231BN Posted May 17, 2020 Report Share Posted May 17, 2020 While it could be the capacitor(condenser), check the ignition leads on the L mag, specifically at the lead nut to make sure the shield hasn't pulled out. Also, check the shield on the P-lead to make sure it's ground connection hasn't broke or come loose. 2 1 Quote Link to comment Share on other sites More sharing options...
Bartman Posted May 18, 2020 Report Share Posted May 18, 2020 I fixed this problem last year with a new set of ignition wires. 1 1 Quote Link to comment Share on other sites More sharing options...
Fry Posted May 18, 2020 Author Report Share Posted May 18, 2020 (edited) 11 hours ago, N231BN said: While it could be the capacitor(condenser), check the ignition leads on the L mag, specifically at the lead nut to make sure the shield hasn't pulled out. Also, check the shield on the P-lead to make sure it's ground connection hasn't broke or come loose. Thanks! Where do I find these leads? Can you point me to a drawing or photo, or precisely describe the location? Edited May 18, 2020 by Fry Quote Link to comment Share on other sites More sharing options...
Fry Posted May 18, 2020 Author Report Share Posted May 18, 2020 13 hours ago, tmo said: ... Apologies for the possibly assinine question but you are sure you have separate magnetos, not a dual mag, right? ... Well I have an IO-360-A3B6D with (I guess) the original mag setup. In my limited understanding this implies that the two magnetos are not completely independent. (do they have a single grounding lead? in that case that cannot be the cause, as I am looking for something specific to the L magneto). I'm sorry but I am still at the beginning of my learning curve. Quote Link to comment Share on other sites More sharing options...
N231BN Posted May 18, 2020 Report Share Posted May 18, 2020 Well I have an IO-360-A3B6D with (I guess) the original mag setup. In my limited understanding this implies that the two magnetos are not completely independent. (do they have a single grounding lead? in that case that cannot be the cause, as I am looking for something specific to the L magneto). I'm sorry but I am still at the beginning of my learning curve. Your dual-mag shares a drive and rotor assembly but it has two of everything else including P-leads and distributors. My advice would be to find a mechanic for this one as you are going to have to replace or repair something.Where are you located? Someone here may be able to help you out. Quote Link to comment Share on other sites More sharing options...
Fry Posted May 18, 2020 Author Report Share Posted May 18, 2020 (edited) 17 hours ago, N231BN said: Where are you located? Someone here may be able to help you out. I just asked my mechanic to look after it - he came back and said something that led me to assume he hasn't looked. I am on the other side of the planet, unfortunately :-) Edited May 19, 2020 by Fry Quote Link to comment Share on other sites More sharing options...
rotorman Posted May 18, 2020 Report Share Posted May 18, 2020 To visually inspect the P leads wires, follow the spark plug wires back to the magneto. On the back where the plug wires go in you will find two round fittings with wires attached. Those are the P leads. You can check that they are tight and visually inspect the wires. 1 2 Quote Link to comment Share on other sites More sharing options...
bradp Posted May 19, 2020 Report Share Posted May 19, 2020 My troubleshooting order for ignition noise would be: P lead shields. Ignition ground plane. After that ignition leads. After that mag issues (I had an E gap that was way out and arcing along the case because of a misrouted and pinched condenser lead. Aaron @select fixed that). 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted May 20, 2020 Report Share Posted May 20, 2020 Great details, Brad! Best regards, -a- Quote Link to comment Share on other sites More sharing options...
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