Radio noise from one of my magnetos

[Ant CB]

Hi all,

I've been trying to troubleshoot a radio noise problem for a while and hit a dead end.

I have an IO-360 with 2 Slick 4300 series mags.

The radio is a handheld ICOM A6 with an external whip antenna. I've swapped the radio with another and all the radio components. The headset and mic plugs are just the ICOM ones that come with the radio.

When I select left only there is no problem. When I select right only I get significant ignition noise through the radio. Also when I'm on both I get it as well. Recently I replaced the left mag with a new one and the right one has just come back from a 500hr inspection. The problem was there before the mag was sent for the 500hr inspection and is still there after.

So far I've....

- Replaced both ignition harnesses with new ones

- Swapped the spark plugs around left to right (problem didn't follow the plugs)

- Replaced the p-leads with mil spec shielded wire and tried them with the shielding connected at both ends and only at the mag end

- Disconnected both p-leads all together

- Checked the condition of the harness and all the harness connections.

None of it seems to make a difference. The interference is so bad it breaks squelch with the squelch almost all the way to max.

I'm at a bit of a loss now. Could it be something wrong with the right mag? It is a Slick 4370 with about 400 hours on it.

[NickAir]

Has it always done this or is this something recent?

Sounds like you have isolated it to the mag or mag harness.

The mag itself was just tested, so check the harness. They go bad.

It sounds like energy leaking or a bad ground causing the problem.

Swap out the mag harness and test it. Good idea to do that every 500 hrs.

Wait for other responses on VAF before you do anything. There are many qualified people to have the solution for you. Good luck.

[RV10inOz]

Take out all your spark plugs, get a good multimeter and measure the resistance from the centre electrode to the contact point inside the plug.

You will need a small file or wet and dry to clean the centre electrode.

Report back with the results...... Any plug reading in excess of 5000 ohms belongs in the bin. Suggest you belt the heck out of it with a hammer so there is no way back into an engine.

You might be surprised.

While you are at it gap them all to 16-18 thou.

[rocketbob]

The mag needs a new condenser.

[Kahuna]

what Pooner Bob said. And Plead shielding gound only one end.

[chaskuss]

Anthony,
Swap your two wiring harnesses. If the problem follows the harness, replace it. If it does not, Bob is correct and you need a new condenser on the left magneto.
Charlie

[Mel]

Everyone talks about the magneto. While that may be a small problem, the bigger problem is probably with your installation.
Be sure the radio is grounded to the airframe. This is the biggest problem I see when using a handheld radio and should eliminate most "noise" problems.

[Ant CB]

Thanks for all the responses.

I'm not an expert on these things, how does a faulty condenser cause the radio noise? Can I simply buy a new condenser, remove the old one and replace or is there more to it than that?

I'm comfortable taking mags on and off and re-setting the mag to engine timing but I've never pulled a mag apart to work on, I just pulled apart a dead one out of curiosity before I threw it in the bin.

[NickAir]

Mel is right about radios commonly have grounding issues. Although, this problem ruled this out if the radio reports interference on only one mag vs. the other mag with out interference. Sounds like the condencer and mag harness are the next steps.

[cfiidon]

Originally Posted by Ant CB

Thanks for all the responses.

I'm not an expert on these things, how does a faulty condenser cause the radio noise?

The condenser/capacitor acts to prevent arcing across the points as they are opening. If it doesn't do it's job, arcing indeed occurs, the points get pitted, and a spark is a broad band radio frequency transmitter, as Marconi found out.

Don