On Tue, 26 Jun 2007 17:45:51 -0500, "Dan Luke"
wrote:


"Peter Clark" wrote:


The GIA2. The GIAs have been swapped and the problem stays.

Sounds like at this point they're going to have to build a harness and
ring out the graycode lines end-to-end from the GIA2 output through to
the AP computer connector individually. If both GIAs are producing
the issue and two AP computers are doing it, there's got to be
something going wrong in the harness. It's all that's left..

Seems logical to me.

The tech says he is talking to Garmin about the possibility that it is a
software problem, although I cannot imagine how such a thing could appear in
only one of many identical airplanes. Faulty memory chip, maybe?

In two different GIAs and two different KAP140s? It seems rather
remote that all four componants would have a software problem that
only manifests itself on the one airframe. I think realistically it's
down to there being a short somewhere. I've not jacked into a KAP140
for quite a while so I don't remember if there's a diagnostic page
which shows the decoded input gray code, but one way for them to try
and isolate which wires on the harness are bad would be to pump the
aircraft up and see if the gray code as shown by the altimeter and
gray code as decoded by the KAP140 A) correlate and B) change with the
test set's altitude. Knowing which wires should be hot for a given
pressure will let you know which ones are bad. Have they tried
hooking up the pitot/staic testset and pumping it up?