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sportav8r(at)gmail.com
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 Posted: Sun Apr 11, 2010 6:17 pm Post subject: intermittent transponder mystery solved |
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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)#$%!
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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Larry Bowen
Joined: 09 Jan 2006
Posts: 802
Location: NC, USA
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| Posted: Sun Apr 11, 2010 6:57 pm Post subject: intermittent transponder mystery solved |
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Excellent detective work! Congrats!!--
Larry Bowen
Larry(at)BowenAero.com
http://BowenAero.com
On Sun, Apr 11, 2010 at 10:15 PM, Bill Boyd <sportav8r(at)gmail.com (sportav8r(at)gmail.com)> wrote:
[quote] 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)#$%!
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
[b]
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_________________
Larry Bowen
RV-8 SOLD,
RV-7QB in progress... |
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libertyva(at)msn.com
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| Posted: Mon Apr 12, 2010 3:57 am Post subject: intermittent transponder mystery solved |
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Stormy,
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.
Date: Sun, 11 Apr 2010 22:15:42 -0400
Subject: intermittent transponder mystery solved
From: sportav8r(at)gmail.com
To: rvsoutheast-list(at)matronics.com; aeroelectric-list(at)matronics.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, 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)#$%!
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
Hotmail is redefining busy with tools for the New Busy. Get more from your inbox. See how. [quote][b]
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ceengland(at)bellsouth.ne
Guest
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| Posted: Mon Apr 12, 2010 4:34 am Post subject: intermittent transponder mystery solved |
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On 4/11/2010 9:15 PM, Bill Boyd wrote:
| Quote: | 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)#$%!
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
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sportav8r(at)gmail.com
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| Posted: Mon Apr 12, 2010 7:13 am Post subject: intermittent transponder mystery solved |
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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
[quote] >>
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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