---------------------------------------------------------- RVSouthEast-List Digest Archive --- Total Messages Posted Sun 04/11/10: 2 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:17 PM - intermittent transponder mystery solved (Bill Boyd) 2. 07:57 PM - Re: intermittent transponder mystery solved (Larry Bowen) ________________________________ Message 1 _____________________________________ Time: 07:17:49 PM PST US Subject: RVSouthEast-List: intermittent transponder mystery solved From: Bill Boyd 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 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 _____________________________________ Time: 07:57:45 PM PST US Subject: Re: RVSouthEast-List: intermittent transponder mystery solved From: Larry Bowen Excellent detective work! Congrats!! -- Larry Bowen Larry@BowenAero.com http://BowenAero.com On Sun, Apr 11, 2010 at 10:15 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 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 > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message rvsoutheast-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/RVSouthEast-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/rvsoutheast-list Browse Digests http://www.matronics.com/digest/rvsoutheast-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.