Why is my right magneto 'eating' condensers?

[Ryan ORL]

So this is a bit of a strange problem.  Starting a few months ago, I started noticing significantly diminished comms reception, and a loud rapid clicking on the comms.  Some brief debugging revealed that it wasn't really comms reception at all, but rather the loud clicking noise was playing hell with the GTN auto-squelch and the problem seemed to be slowly getting worse. 

Some further troubleshooting revealed that the problem was only evident on the RIGHT magneto, i.e. the clicking noise disappeared entirely when running only on the LEFT magneto, and the clicking was certainly RPM dependent.  It was easy enough to break squelch on COM1 and just listen to the click disappear and reappear when switching the mags.

My local shop started debugging this, first checking for loose grounds (etc) and checking the magneto harness for pinching, chafing, or arcing.  They found one slightly loose shield and corrected that.  They did some kind of high voltage test on the harness (~110 hours old, new at my recent engine overhaul) and found no problems.  There was also nothing visually obviously wrong with the harness or leads.

So I did a bit of further debugging with a portable radio.  The clicking was actually audible on the portable comm radio with all my aircraft electrical systems entirely turned off, in other words it was most definitely arcing somewhere, and our assumption was it was inside the magneto.

Sure enough, the shop tested the condenser and found it was a bit out of spec, and they put in a known-good spare that they had while we ordered a new one and waited for delivery.  That cured the clicking entirely.  Comms totally quiet on either mag.  Hooray!  As an engineer myself I also wanted to understand what went wrong... so fortunately this also entirely made sense... a bad condenser would lead to the points arcing, case closed, I thought.

The new condenser is due to arrive this week, so I am still flying on the 'spare' one.  I had around 5-6 trouble-free flying hours on it.  But on Saturday when I went to fly the airplane... the clicking was back!  Now, we haven't had a chance to dig into this yet... we're of course going to install the new condenser, but my concern is that either I am just enormously unlucky, or something else is killing the condenser and the new one will just fail again.

So does anyone have any theories on what the hell might be going on inside this magneto?  The mag itself is relatively recent... 110 hours also, from the overhaul, it was an overhaul unit from Quality Aircraft Accessories.  At this point I suspect there must be some other internal fault there... I am inclined to just send the whole thing out for overhaul or even try to get an exchange unit.  I am honestly tired of chasing the issue.  Could it also be something with my plugs on that side?  I run all Tempest Fine Wires that have maybe a few hundred hours on them.

[PT20J]

I’d wait for the new part and see what happens after it is installed. It’s always possible that the spare part that may have been sitting on a shelf for who knows how long is defective. 

[EricJ]

Sometimes it's also the act of removing/replacing the part that re-seats the part or the fasteners to re-establish a good ground or connection.   

[Fritz1]

as stated supra, install new condenser and see what happens, during COVID I had two dud mag overhauls from QAA, may have been a coincidence, use Aircraft Accessories of Oklahoma now with good success

[Ryan ORL]

Going to try that and see what happens, thanks everyone!

[MikeOH]

23 minutes ago, Ryan ORL said:

Going to try that and see what happens, thanks everyone!

If the truly new cap fails in a short time, I'd be looking at high-voltage breakdown inside the mag.  Capacitors don't take kindly to overvoltage and the only place that's going to come from is the secondary (high-voltage) part of mag 'bleeding' into the primary side (points and cap).

[GeeBee]

Usually a mag that fries condensers has a bad coil. Coils are not replaced on overhauls, just checked with a VOM. Coils often are intermittent. Go ahead and use the new unit and see how far that gets you. They are cheap. If it fries again it is the coil. 

I'm not a fan of O/H magnetos unless they are O/H by Aircraft Magneto Service. He is a little more but I've never gone wrong with one of his units. Usually I just buy new because on the Continentals it is not that much more, but my last one there was no stock so I used AMS and once again the service was superb. The main problem with O/H exchange is there is too many crappy cores out there that get by the overhaul facility. AMS is pretty good at sorting those out although I have never done an exchange others I know have.

https://www.aircraftmagnetoservice.net

[Ryan ORL]

Mike and GeeBee, that theory sounds very plausible to me!  Will definitely report back what happens w/ the new condenser.  I suspect you're right.