Newsgroups: rec.aviation.student
From: trisoft@realtime.net (James M. Knox)
Subject: Re: GPS=backup : realworld example
Organization: TriSoft/CyberSearch
References: <71nkrm$vl5$1@nnrp1.dejanews.com>
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In article <71nkrm$vl5$1@nnrp1.dejanews.com>, msheppard@yahoo.com wrote:
>I've got a Garmin12xl which (usually) works great for flying.

>Back at home I reproduced the problem, just banging it would make it go off. 
>I was a little worried.  I took the batteries out, switched them around, and
>put them back in and now it never happens.  Haven't flown since then, but I'm
>wondering if anyone else has seen this behaviour, either in GPS or other on-
>board electronics that take batteries.

Sounds like weak springs on the battery contactors and/or slightly tarnished 
contacts.  

BTW, another problem that can cause this on many Garmin models -- Garmin uses 
an active antenna (small amp in the antenna) and drives power through the 
antenna coax.  An intermittent shield wire (shorting within the BNC connector 
at either end) will cause the thing to just shut off.  Just like a low battery 
problem, except no warning.  Just "blinks" off.  Turns on again fine - until 
the next time it does it.

                                                jmk
