Today's Message Index:
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1. 04:57 AM - Re: intermittent transponder mystery solved (BOB MARTIN)
2. 05:34 AM - Re: intermittent transponder mystery solved (Charlie England)
3. 08:13 AM - Re: intermittent transponder mystery solved (Bill Boyd)
Message 1
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| Subject: | intermittent transponder mystery solved |
Stormy=2C
Great write up........Thanks for sharing! The Pictures were a nice touch.
I can see why it was such a problem.
Bob Martin
RV-6 Louisa VA.
Subject: RVSouthEast-List: intermittent transponder mystery solved
From: sportav8r@gmail.com
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=2C using Garmin's plug-and-play adapter to fit between the
two. The first time it crapped-out=2C I sent the transponder back to Garmi
n: $250 bench fee to be told the box is fine. Worked fine for awhile afte
r that. Then it started becoming intermittent - the interrogation light wo
uld flicker normally at the start of a cross-country=2C and ATC could give
me VFR advisory service=2C 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=2C but the prospect of having to enter
the Orlando mode C veil next week with "known issues" motivated me to try a
gain. I started with what has worked before - removing the transponder and
adapter tray=2C spraying every connection with contact cleaner and reassem
bling it all. Well=2C that worked for a few seconds and then it quit again
=2C so I got out the continuity checker and started checking the RF path fo
r 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
=2C and sure enough=2C if I held the coax a certain way=2C I saw interrogat
ion flashes=3B if I let go=2C 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=3B the male mating plug
on the front side of the adapter looked good - no bent pin. The female jac
k 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=2C but it is totally
protected inside the chassis and is under no mechanical strain=2C and it's
new Garmin manufacture=2C 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 Narc
o 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=2C and i
ts coax shield is well-crimped and fully strain-relieved. Maybe the male p
in on the end of that pigtail=2C the one that's captive in the back of the
tray=2C is worn/undersize. So I added a thin layer of solder to the gold p
in and pressed it back into the fitting on the Garmin adapter tray - still
showed an intermittent open when I wiggled it! @#$%!
At this point=2C I noticed that as I twisted the jack into the plug=2C the
shell of the Garmin female (the barrel) would move with it. That's not sup
posed to happen. In fact=2C the entire guts of the Garmin female fitting is
threaded into its mounting flange=2C and since it is not secured or safeti
ed in any way (and was doubtless under-torqued at assembly)=2C movement of
the male coax pigtail on the outside of the tray eventually broke the BNC s
older connection inside the Garmin adapter. I re-threaded the outer shell
of the Garmin adapter's female connector with red LocTite and re-soldered t
he mini-coax to it. Problem fixed - hopefully for good!
Moral of the story: never assume that a factory avionics assembly is proper
ly done=2C 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=2C the fitting as it come
s apart but isn't supposed to=2C and how it broke the solder joint internal
ly. The last one shows the guts of the BNC fitting completely unscrewed fr
om its mounting flange and the coax just hanging there. May this never hap
pen to you! :-) If it does=2C remember to question everything you're ass
uming.
I'm gonna feel bad if the pictures don't upload - never done that on Matro
nics list before.
-Bill B. / "Stormy" RV-6A
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Message 2
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| Subject: | Re: intermittent transponder mystery solved |
On 4/11/2010 9:15 PM, Bill Boyd 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
>
>
>>
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...
> >
Congrats on 'slaying the beast'.
Here's some food for thought. I spent most of two previous lives as an
electronics tech, one on consumer electronics and the other on
industrial gear. About 98% of the problems I fixed were manufacturer
problems. (And most of the time I wasted chasing ghosts was due to
making the same assumption you made.)
FWIW,
Charlie
Message 3
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| Subject: | Re: intermittent transponder mystery solved |
I bet Garmin received that RF connector already screwed together and never
questioned its integrity. I'd be willing to give them the benefit of the
doubt and say it's probably a first such failure for that product. There
can't be a huge call for Narco to Garmin adapters.
Bob, why do we always find things in the last place we think to look?!
-Stormy
>> >>
> 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...
>
>> >
>>
>
> Congrats on 'slaying the beast'.
>
> Here's some food for thought. I spent most of two previous lives as an
> electronics tech, one on consumer electronics and the other on industrial
> gear. About 98% of the problems I fixed were manufacturer problems. (And
> most of the time I wasted chasing ghosts was due to making the same
> assumption you made.)
>
> FWIW,
>
> Charlie
>
>
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