Jump to content

trt 250 transponder

Recommended Posts

looking for an old trt 250 for the push buttons and gear for changing the code. mine works fine except the first number will only go to 3. appears the gear is worn to the point where the gear wont move the number anymore. no one has any parts for these anymore.:)

Rebel Wallace

Link to comment
Share on other sites

If you know digital electronics you can replace the switches yourself.


Do a google search for "BCD switch" and ignore the "business directories".


A little hacking and you're done. It doesn't have to be "push button", "thumbwheel" versions works just as well.


Drawback is you have to know the encoding pattern (code table) for your particular switches and make sure the replacement match the output pattern. It's easy enough to make up your own "code table" once you remove the switches and find a replacement that match the same coding. This link gives an example of a "BCD code table": http://www.elexp.com/t_bcd.htm.


Of course the transponder would no longer be "certified", but if your airplane is an experimental and the transponder output on the correct frequencies (have it tested properly to make sure), I think you may be okay. (Not sure, so check on the "legalities".)


Not sure what else I can say, except that if this was mine, I would just replace the "push button" switches with a homebrew electronic display (LED), some logic gates and momentary contact switches.


"All of my ideas are suspect until proven otherwise!"

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information