Intermittent Transponder

[jimmyjack]

The replacement KT76A is on its way, but for sake of discussion I thought I'd post my situation.

My EDO AIRE RT-777 Transponder is acting intermittently.

First off, it's shoved (actually nicely installed) in my 172's glove box. A couple weeks ago, it was working fine, then ATC reported primary target only and to recycle. This was mid-flight and it didn't come back.

Upon landing, I remembered I put the Ohio AFD in the glove box, right atop the transponder. It was almost too hot to touch when I pulled the book out.

Overheated it, probably permanently destroyed it. Lesson learned.

The next day, on a whim, I went up and it was working fine. Day after that, working fine. So after cooling down, it's good to go, right?

Perhaps not. This past Sunday we took off for a day trip. Worked all the way to the destination and 90% of the way back. 10 miles from home ATC confirmed primary target only. Book, this time, is in the baggage compartment. Xponder is all by itself, as it always has been.

Waited a day, tried again, still primary target only.

Landed, pulled it out. Pulled the cover off, inspected resistors, capacitors, etc. I don't really know what I'm looking at, but nothing looked burnt or bulged.

Cleaned connections, reinstalled, tried again. Primary target only.

Like I said RT76A will be here in two days, but wanted your guys' thoughts. My A&P begged me to just buy another one, she has no respect for the EDO AIRE's.

FWIW, the install job in the glove box was very clean. They cut a hole through the glove box lid and did a professional job, but they didn't put an exhaust hole in the back of the box, so really it's a big aluminum microwave.

 

[RPaulson]

That transponder is at least 33 years old, probably closer to 40. At that age, electronics just quit. No rhyme or reason to it.

Ryan

 

[unsafervguy]

the question is, if you are going to replace it, why replace it with a transponder with a cavity tube? replace it with a solid state device and I would go with a mode S looking toward 2020.

bob

 

[MikeS]

This will sound too simple, but how clean is your antenna? Located down on the bottom right in the exhaust stream or close to it, it becomes coated with grime and is responsible for many many transponder problems that clear right up once you clean the antenna. Surely you checked that, but it's such a common phenomenon thought I'd mention the obvious.

 

[weirdjim]

This will sound too simple, but how clean is your antenna? Located down on the bottom right in the exhaust stream or close to it, it becomes coated with grime and is responsible for many many transponder problems that clear right up once you clean the antenna. Surely you checked that, but it's such a common phenomenon thought I'd mention the obvious.

Jim

 

[jimmyjack]

This will sound too simple, but how clean is your antenna? Located down on the bottom right in the exhaust stream or close to it, it becomes coated with grime and is responsible for many many transponder problems that clear right up once you clean the antenna. Surely you checked that, but it's such a common phenomenon thought I'd mention the obvious.

I did check the antenna. It was clean enough, though I wiped it down again.

Moot point, the KT76A is installed and working great. A&P did advise she had to order a compatible replacement antenna as what I had was incompatible with the King.

 

[weirdjim]

I did check the antenna. It was clean enough, though I wiped it down again.

Moot point, the KT76A is installed and working great. A&P did advise she had to order a compatible replacement antenna as what I had was incompatible with the King.

I'd sure like to know what is so special about the King that it requires a specific antenna.

Jim


.

 

[jimmyjack]

I'd sure like to know what is so special about the King that it requires a specific antenna.

Jim
.

It was probably more that the oddball Edo Aire required a proprietary, but I have no idea.

 

[nrpetersen]

I can't think of anything harder to diagnose remotely than a 33 year old transponder.................