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1. 07:17 PM - intermittent transponder mystery solved (Bill Boyd)
2. 07:57 PM - Re: intermittent transponder mystery solved (Larry Bowen)
Message 1
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| Subject: | intermittent transponder mystery solved |
I finally ran to ground my transponder intermittent that has been plaguing
me for years! My set-up is a Garmin GTX 320 in a tray that formerly housed
a Narco AT-150, using Garmin's plug-and-play adapter to fit between the two.
The first time it crapped-out, I sent the transponder back to Garmin: $250
bench fee to be told the box is fine. Worked fine for awhile after that.
Then it started becoming intermittent - the interrogation light would
flicker normally at the start of a cross-country, and ATC could give me VFR
advisory service, but often by the time I got to the destination I was only
showing as a primary target on radar.
I limped along like this for awhile, but the prospect of having to enter the
Orlando mode C veil next week with "known issues" motivated me to try again.
I started with what has worked before - removing the transponder and
adapter tray, spraying every connection with contact cleaner and
reassembling it all. Well, that worked for a few seconds and then it quit
again, so I got out the continuity checker and started checking the RF path
for opens and shorts. The meter showed an open on the coax center conductor
when I wiggled it in the back of thel Narco tray. Put the innards back in,
and sure enough, if I held the coax a certain way, I saw interrogation
flashes; if I let go, it stopped. Now all I need is for the pax to reach
under the panel and hold the coax the whole trip. Not happening.
The BNC jack on the transponder itself looked good; the male mating plug on
the front side of the adapter looked good - no bent pin. The female jack in
the back of the Garmin-to-Narco adapter looked good. There is a small
length of RG-184-type teflon coax inside the adapter, but it is totally
protected inside the chassis and is under no mechanical strain, and it's new
Garmin manufacture, so the problem can't be there <hold that thought> so the
fault must be in that ancient RG-58 pigtail that came with the Narco tray
and was probably soldered in the 1950's. But the continuity checker showed
no opens or shorts no matter how I wiggled it on the bench, and its coax
shield is well-crimped and fully strain-relieved. Maybe the male pin on the
end of that pigtail, the one that's captive in the back of the tray, is
worn/undersize. So I added a thin layer of solder to the gold pin and
pressed it back into the fitting on the Garmin adapter tray - still showed
an intermittent open when I wiggled it! @#$%!
At this point, I noticed that as I twisted the jack into the plug, the shell
of the Garmin female (the barrel) would move with it. That's not supposed
to happen. In fact, the entire guts of the Garmin female fitting is threaded
into its mounting flange, and since it is not secured or safetied in any way
(and was doubtless under-torqued at assembly), movement of the male coax
pigtail on the outside of the tray eventually broke the BNC solder
connection inside the Garmin adapter. I re-threaded the outer shell of the
Garmin adapter's female connector with red LocTite and re-soldered the
mini-coax to it. Problem fixed - hopefully for good!
Moral of the story: never assume that a factory avionics assembly is
properly done, or that a wire that "can't possibly" move/break hasn't done
just that. I only wish that there was some lifetime warranty where the
Garmin would comp me for the time and aggravation this has caused.
I'm attaching pictures that show the adapter tray, the fitting as it comes
apart but isn't supposed to, and how it broke the solder joint internally.
The last one shows the guts of the BNC fitting completely unscrewed from
its mounting flange and the coax just hanging there. May this never happen
to you! :-) If it does, remember to question everything you're assuming.
I'm gonna feel bad if the pictures don't upload - never done that on
Matronics list before.
-Bill B. / "Stormy" RV-6A
Message 2
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| Subject: | Re: intermittent transponder mystery solved |
Excellent detective work! Congrats!!
--
Larry Bowen
Larry@BowenAero.com
http://BowenAero.com
On Sun, Apr 11, 2010 at 10:15 PM, Bill Boyd <sportav8r@gmail.com> wrote:
> I finally ran to ground my transponder intermittent that has been plaguing
> me for years! My set-up is a Garmin GTX 320 in a tray that formerly housed
> a Narco AT-150, using Garmin's plug-and-play adapter to fit between the two.
> The first time it crapped-out, I sent the transponder back to Garmin: $250
> bench fee to be told the box is fine. Worked fine for awhile after that.
> Then it started becoming intermittent - the interrogation light would
> flicker normally at the start of a cross-country, and ATC could give me VFR
> advisory service, but often by the time I got to the destination I was only
> showing as a primary target on radar.
>
> I limped along like this for awhile, but the prospect of having to enter
> the Orlando mode C veil next week with "known issues" motivated me to try
> again. I started with what has worked before - removing the transponder and
> adapter tray, spraying every connection with contact cleaner and
> reassembling it all. Well, that worked for a few seconds and then it quit
> again, so I got out the continuity checker and started checking the RF path
> for opens and shorts. The meter showed an open on the coax center conductor
> when I wiggled it in the back of thel Narco tray. Put the innards back in,
> and sure enough, if I held the coax a certain way, I saw interrogation
> flashes; if I let go, it stopped. Now all I need is for the pax to reach
> under the panel and hold the coax the whole trip. Not happening.
>
> The BNC jack on the transponder itself looked good; the male mating plug on
> the front side of the adapter looked good - no bent pin. The female jack in
> the back of the Garmin-to-Narco adapter looked good. There is a small
> length of RG-184-type teflon coax inside the adapter, but it is totally
> protected inside the chassis and is under no mechanical strain, and it's new
> Garmin manufacture, so the problem can't be there <hold that thought> so the
> fault must be in that ancient RG-58 pigtail that came with the Narco tray
> and was probably soldered in the 1950's. But the continuity checker showed
> no opens or shorts no matter how I wiggled it on the bench, and its coax
> shield is well-crimped and fully strain-relieved. Maybe the male pin on the
> end of that pigtail, the one that's captive in the back of the tray, is
> worn/undersize. So I added a thin layer of solder to the gold pin and
> pressed it back into the fitting on the Garmin adapter tray - still showed
> an intermittent open when I wiggled it! @#$%!
>
> At this point, I noticed that as I twisted the jack into the plug, the
> shell of the Garmin female (the barrel) would move with it. That's not
> supposed to happen. In fact, the entire guts of the Garmin female fitting is
> threaded into its mounting flange, and since it is not secured or safetied
> in any way (and was doubtless under-torqued at assembly), movement of the
> male coax pigtail on the outside of the tray eventually broke the BNC solder
> connection inside the Garmin adapter. I re-threaded the outer shell of the
> Garmin adapter's female connector with red LocTite and re-soldered the
> mini-coax to it. Problem fixed - hopefully for good!
>
> Moral of the story: never assume that a factory avionics assembly is
> properly done, or that a wire that "can't possibly" move/break hasn't done
> just that. I only wish that there was some lifetime warranty where the
> Garmin would comp me for the time and aggravation this has caused.
>
> I'm attaching pictures that show the adapter tray, the fitting as it comes
> apart but isn't supposed to, and how it broke the solder joint internally.
> The last one shows the guts of the BNC fitting completely unscrewed from
> its mounting flange and the coax just hanging there. May this never happen
> to you! :-) If it does, remember to question everything you're assuming.
>
> I'm gonna feel bad if the pictures don't upload - never done that on
> Matronics list before.
>
> -Bill B. / "Stormy" RV-6A
>
>
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