Wrathall Mark wrote:

Perry Mick, could you please write a page detailing symtoms, troubleshooting
and modification procedures for the Mazda Lead Coil resister failure.

Thanks for the request Mark.  I can't really answer the question though.
First Tracy had a failure, then Ed Anderson I believe, and then Chuck Dunlap.
Three failures indicate there is certainly a weakness.  Although I'm trying
to understand it, I don't, as I haven't looked at the waveforms with the
engine running at 6000 RPM.  I could, since I have an RX-7 and access
to a portable scope.  Maybe I'll do that one of these days, and take
scope pictures of the waveforms.  Then we can estimate power dissipated
in the resistor.  My guess is it's just a combination of high ambient temperature
under the cowl combined with higher power dissipation in the resistor at
high RPM.  Resistors are "derated" at elevated temperature, that is, they
cannot handle the same power dissipation at high temperature that they
can at room temperature. Mine has not failed after 160 hours and probably 10
years in a car before that.  But I run the engine at 4700-5100 RPM in flight,
except during descent.

The failure would manifest as loss of leading ignition, since the resistor
fails open, and the coil loses it's source of 14V power.

I would just recommend everyone make the mod to be safe.  You can
put three 1ohm 5watt resistors in parallel inside the coil, by making your own
mounting plate out of aluminum, as shown in the attached drawing.
Dale part number RH-5 1ohm.
--
Perry Mick
Duckt N7XR
http://www.ductedfan.com

 
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