I was researching the failure on John Slades EC2 and found some
disturbing things.
The input power filter uses a choke which is the only single failure
point in the EC2. The part was originally specified to be so over
rated such that failure could only be caused by physical damage to
the part. If an overload occurred sufficient to fail this part, the
circuit traces on the board would fail long before the part would. This
was the rationale for the basic design approach. Don't want to get into
a discussion of why separate chokes are not used.
At some point the manufacturing facility substituted a different part
with same inductance but lower current rating. It was still over rated
and sufficient for any foreseeable situation so it was considered OK.
Still later, the board maker substituted an even lower rated part that
looks almost identical to the previously substituted part. I was not
informed of this change. The unit will function normally with this
part but it has no extra margin for safety in the event of mis wire,
shorted output, etc. I was able to duplicate the failure John Slade had
by shorting 1 or more ignition driver outputs to ground or 12V input
power. The original design intent was to allow this condition without
failure of the choke.
Point of this message is to announce an AD (airworthiness directive) to
inspect and verify the type of choke used on your EC2. Attached to this
message is a picture of the three types of chokes used. The left is the
originally specified part. The center part is an acceptable substitute
part. The right hand part is the unacceptable choke. If you have this
part, do not fly the aircraft until it has been replaced. In addition
to the visual difference, you can determine which part by measuring the
resistance. The bad part has a resistance over 10 ohms. The correct
parts are much lower in resistance.
We will replace the part for you for no charge except shipping cost as
specified in the warranty. This is a simple through-hole soldered part
that is relatively easy to replace. If you are qualified to replace the
part yourself, we will send the correct part at no cost.
Tracy Crook
Real World Solutions Inc.
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