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Date: Tue, 06 Apr 2010 07:59:12 -0400
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Subject: fixes for S-TEC 50 alt hold
From: Keith Smith <keith.smith@gmail.com>
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The altitude hold function on my LNC2 never worked since the day I bought
the airplane (coming up on 12 months ago).  I'll leave out all of the things
we tried to fix it that had no effect, and limit it to the relevant steps
that actually had a positive change.  Note, the alt hold is now working very
well (with one caveat, which I'll note at the end).  The purpose of posting
this is to have it in the archive, in case anyone else runs into similar
issues with their AP in the future.

- trim indicators (ie, add up trim, add down trim) were reversed
- pitch servo was reversed
- pressure transducer (pin 16) was apparently wired with someone counting
the pins from the wrong part of the connector, so no static port data was
reaching the AP

All of those things were fixed, resulting in an altitude hold that almost
worked perfectly. It was a good 1/2 - 1 second 'behind' the airplane.

The final fix was to disconnect the static line from the pressure
transducer, venting it to the cabin.  For an STEC-50, which only has
altitude hold (doesn't have the ability to maintain a specified altitude),
this was a great solution.

Now it works like a champ!

The only hitch now is that when I transmit on radio, the alt hold (and hdg
hold for that matter, but it's less noticeable) functions are significantly
disrupted.  My guess is that the transmission from the com radio is hurting
the signal from the pressure transducer back to the AP. I am going to
research the possibility of adding some shielding to that cable.

Keith

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The altitude hold function on my LNC2 never worked since the day I bought t=
he airplane (coming up on 12 months ago).=A0 I&#39;ll leave out all of the =
things we tried to fix it that had no effect, and limit it to the relevant =
steps that actually had a positive change.=A0 Note, the alt hold is now wor=
king very well (with one caveat, which I&#39;ll note at the end).=A0 The pu=
rpose of posting this is to have it in the archive, in case anyone else run=
s into similar issues with their AP in the future.<br>
<br>- trim indicators (ie, add up trim, add down trim) were reversed<br>- p=
itch servo was reversed<br>- pressure transducer (pin 16) was apparently wi=
red with someone counting the pins from the wrong part of the connector, so=
 no static port data was reaching the AP<br>
<br>All of those things were fixed, resulting in an altitude hold that almo=
st worked perfectly. It was a good 1/2 - 1 second &#39;behind&#39; the airp=
lane.=A0 <br><br>The final fix was to disconnect the static line from the p=
ressure transducer, venting it to the cabin.=A0 For an STEC-50, which only =
has altitude hold (doesn&#39;t have the ability to maintain a specified alt=
itude), this was a great solution.<br>
<br>Now it works like a champ!<br><br>The only hitch now is that when I tra=
nsmit on radio, the alt hold (and hdg hold for that matter, but it&#39;s le=
ss noticeable) functions are significantly disrupted.=A0 My guess is that t=
he transmission from the com radio is hurting the signal from the pressure =
transducer back to the AP. I am going to research the possibility of adding=
 some shielding to that cable.<br>
<br>Keith<br>

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