trt 250 transponder

[REBEL777]

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.

[WileEZ]

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.