Transponder Issues

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tpowers

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tpowers
I purchased a Cessna 150 last September and have been having intermittent issues with it's transponder. Sometimes the Mode-C would go out, other times it would drop off the radar altogether.

It's a Narco AT50. I've been reading up on possible problems and the most common suggestion is to clean the contacts. I've done that with a can of Electro-wash both on the unit itself and in the connecting ports inside of the docking tray. However my problems persist.

Another potential culprit is the antenna. I noticed the antenna was mucky with a combination of dirt and oil so I went to gently clean it and as I did the antenna popped out of it's socket. Now, I'm new to this kind of stuff so I can only assume, based on all of the antennas that I've seen in the past, that they shouldn't just pop off. So unless there's something strange about transponder antennas I'm assuming at this point that it was a broken antenna which the previous owner just shoved back into the socket and hoped it would a) make some kind of contact allowing a signal to go through or at least b) look like an operable transponder antenna so some sucker (me) would buy the plane.

If, however, anyone knows of any reason why a transponder antenna should pop out with a gentle tug then please let me know. Also, assuming I'm going to be replacing this antenna, is there anything I should know? Is it as simple as unbolting the socket and bolting in another one or am I in for a surprise?

P.S. I know there are many different types of transponder antennas, this one is similar: http://www.skygeek.com/ted-104-12-transponder-antenna.html?utm_source=googlebase&utm_medium=shoppingengine&utm_content=ted-104-12-transponder-antenna&utm_campaign=froogle&gclid=CM_48vrL18oCFQymaQodascLRA
 
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Might be time to change out the older unit for a new one,the antenna may have been installed with some sort of sealant ,to prevent moister leakage,.
 
Clean your contacts with a eraser. Red/pink ones work best. #2 pencil erasers are good. Thais has worked for me many times.
 
no,the rod should not come out of the connector. replace it. there is a good chance that is the problem. don't let anybody talk you in to a more expensive antenna. those work just fine.

bob
 
I had someone who has recently purchased the Garmin 327. It had cost him around $2000-$2500 for purchase+install+certifie.
 
unsafervguy said:
no,the rod should not come out of the connector. replace it. there is a good chance that is the problem. don't let anybody talk you in to a more expensive antenna. those work just fine.

bob
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Thought not :) okay I'll try replacing it. Thanks
 
Okay purchased the new antenna. I would like to put it in myself. I can't seem to figure out for the life of me how to get access to the back-side of the antenna where the coax connects. The antenna is located on the belly and seems to be just forward of the rudder pedals (this is a 1971 model L).

There is an inspection panel near the antenna but after removing it it doesn't provide access to it because there's a wall between the inspection panel and the antenna.
 
tpowers said:
Okay purchased the new antenna. I would like to put it in myself. I can't seem to figure out for the life of me how to get access to the back-side of the antenna where the coax connects. The antenna is located on the belly and seems to be just forward of the rudder pedals (this is a 1971 model L).

There is an inspection panel near the antenna but after removing it it doesn't provide access to it because there's a wall between the inspection panel and the antenna.
Click to expand...

You might want to check in with the A&P will eventually sign off your work.
 
If it is aft of bulkhead 28 in pic, you can take off "feet pans" 65/6 - more likely.
If it is fore of 28, there are rudder bar covers to remove; 42A-9 & 10 (not much room here, I doubt it.
 

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Let'sgoflying! said:
If it is aft of bulkhead 28 in pic, you can take off "feet pans" 65/6 - more likely.
If it is fore of 28, there are rudder bar covers to remove; 42A-9 & 10 (not much room here, I doubt it.
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Thank you, I will check it out today :)
Out of curiosity where did you get this diagram from?
 
Thanks. Got it installed yesterday. I like to follow up on posts like this for the sake of people googling in the future with the same issues.

Turns out my memory was faulty and the placement of the antenna was quite a bit further back than I had remembered. In this particular model (1971 Cessna 150-L) the back side of the transponder antenna can be accessed by one of two inspection panels under the carpet immediately in front of the seats.

The easiest way would be to remove the metal stripping holding the carpet in place which is right in front of the seats, remove the handle for the fuel cut-off valve, remove the small plastic plaque on the floor which instructs you on how to use the fuel cut-off valve, then pull forward the carpet to get access to two round inspection panels in the center.
 
Don't know if you could use it but I just removed an ARC RT-459A transponder and AK-350 encoder from the Lancair. Perfect working condition, they just passed certification in December. Asking $400.
 
I believe my problem was caused by the antenna and the transponder itself probably works fine. Eventually I'll replace it with an ADS-B compatible transponder.

For now my plane is grounded due to the FAA taking their sweet time to get the registration paperwork through and my temporary having expired so I won't know for sure if my antenna replacement did the trick for another few weeks.
 
The cheap metal antennas plastic insulators crack and the antenna no longer works. Common. When that happens, ATC only sees primary. I've also had them stop simply due to grime and cleaning them fixes it.


Sent from my iPad using Tapatalk
 
Well did a test flight yesterday and to my surprise my problem persists. Obviously that antenna couldn't have been good but there must be something more going on.

The FBO in my neck of the woods, I don't really trust. I talked with them about this issue and they said all they could do is clean the contacts (which I already did). The only work I've asked them to do so far is stop my wheel from squeaking and $75 later it still squeaks so if they can't get that right I'm no going to trust them with avionics either.

I don't really want the expense of a brand new transponder at this time and I don't want to spend too much to get it working (such as replacing with with a 2nd hand) because I do plan on replacing it with an ADS-b transponder in the future.

I guess it's time to send it in somewhere for repairs. A quick google search pops up www.transponderrepair.com as the first hit and they do repair this particular model (Narco AT50-A).

Does anyone have any experience with this site, or could recommend other options?
 
tpowers said:
Well did a test flight yesterday and to my surprise my problem persists. Obviously that antenna couldn't have been good but there must be something more going on.

The FBO in my neck of the woods, I don't really trust. I talked with them about this issue and they said all they could do is clean the contacts (which I already did). The only work I've asked them to do so far is stop my wheel from squeaking and $75 later it still squeaks so if they can't get that right I'm no going to trust them with avionics either.

I don't really want the expense of a brand new transponder at this time and I don't want to spend too much to get it working (such as replacing with with a 2nd hand) because I do plan on replacing it with an ADS-b transponder in the future.

I guess it's time to send it in somewhere for repairs. A quick google search pops up www.transponderrepair.com as the first hit and they do repair this particular model (Narco AT50-A).

Does anyone have any experience with this site, or could recommend other options?
Click to expand...

Your transponder needs to be checked every 24 months..... Is that check coming up soon ?
 
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