REFLECTOR: Intercom noise

[aminetech at bluefrog.com]

I tried using the Bendix filter.  Not only did it not help, the mag did not work at all.  To summarize, what I know is that the mag is associated with the noise.  The problem has existed for a few years, but is more noticeable now as I am doing my IFR training and need to communicate with the instructor.  Also the noise is slightly intermittent, but mostly constant.  More intermittent at startup and low rpm.  Something else I need to fess up, before I bought this plane, it was worked on to correct deficiencies.  Triple "0" wire was installed for the starter.  I suspect this was done because it won't crank when the engine is hot, but that didn't fix that problem.  I now have a larger battery and that did the trick.  Anyway, when the wire was installed, they tried to start the engine, but forgot to connect the ground.  I was there when it happened.  The engine turned slowly as if the battery was dead.  I saw a puff of smoke come out the intercom.  I suppose an intelligent person would have run for the door, but I was bitten by the Velocity bug and this was the one I wanted.  Plus I was assured that everything would be checked and made right.  So I returned a few weeks later and handed over a check.  The alternator warning light was on very dim and I was told that it wasn't working right.  Since I was the novice, I felt I should trust the experts.  So I flew it home and everything seemed ok.  Several flights later I had power failure while on a cc flight.  Guess the warning light wasn't malfunctioning after all.  I found that the alternator output wire was nearly burned in half where it connected to the filter.  This must have happened when the starter ground was not connected, and the alternator wire had just enough contact to work for a few weeks.  I don't understand how current travels from the starter to the alternator output wire.  If someone can explain that I would like to know.  Anyway, I wonder if there is another ground somewhere that is damaged.  Any ideas of where the current from the starter would likely travel would be helpful.

John

--- michalk at awpi.com wrote:

From: Brian Michalk <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Subject: Re: REFLECTOR: Intercom noise
Date: Sat, 08 Jan 2011 22:21:38 -0600

I'm not an expert on magneto construction, but I agree it's strange.  
Not something I would expect.  The best part about this is that you 
stuck with it, narrowing the problem down to the magneto.

Some lipstick might be okay.  The problem I have with it is that 
something unknown is radiating that in the past did not radiate.  This 
indicates to me that something is broken somewhere, and could get 
worse.  The worst thing one can do is treat the symptom by addressing 
the intercom problem.  The true problem is the magneto.

The lipstick is okay whenever you pinpoint a very specific cause of an 
event.  You look at what the cause is, and determine for whatever reason 
that the radiating offender is nominal.  In those cases, It's okay to 
treat the symptom.  For a noisy intercom, I would add power filters, or 
do what's necessary.

Otherwise, consider the intercom noise as a gift to you telling you that 
something broke somewhere and needs maintenance.

On 01/08/2011 08:41 AM, aminetech at bluefrog.com wrote:
> Brian,
>
> If a bad plug wire is causing the noise, shouldn't the noise go away when I turn off the mag?  It doesn't, so I'm thinking the issue is within the mag.  I'm tempted to try a little lipstick before replacing wires.
>
> John
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