Transponder doesn't work until I push it in

[ryoder]

My transponder doesn't light up sometimes until I push in on it. Then it begins replying like crazy. Does that mean the tray is loose or something? It's an old King Mode C.

[philiplane]

Depends on the model. Is it a King or Narco, or something else? Both of those use cams to pull the unit into the tray. If it is seated properly, then your problems may be in the faceplate to chassis connection.

[BigTex]

Have you tried to removing it, cleaning the connectors and re-seating in back in the rack?

[Mooneymite]

If it's some version of a KT-76, use a hex wrench to loosen it and unlock the cam, pull it in and out of the tray a couple of times to clean the contacts.

 

As I recall, the KT-76 retention works just like on the KT 170 series radios....the one screw accessible through the face-plate controls a nylon cam to loosen and then turn the cam.  It is possible to destroy the cam by forcing it....use some care.  Gently wiggle the unit side by side rather than trying to pull an unwilling unit from the panel...

 

Naturally the re-installation would be done by a "qualified technician", right?  

[jetdriven]

push it in, tighten the set screw, push it in a little firmer, rock it side to side, keep repeating the sequence until its seated fully. KX-170B and KLN-89B GPS's do this too.

[ryoder]

Yeah it's a kt76 and my cfi is an a&p and he said he cleaned the contacts but it's still doing it. It's just not in tight enough. I'll try these suggestions, thanks.

[M20S Driver]

Yeah it's a kt76 and my cfi is an a&p and he said he cleaned the contacts but it's still doing it. It's just not in tight enough. I'll try these suggestions, thanks.

Similar problem on my old C-182 turned out to be caused by a broken wire.  

[Alhall]

Look at the pins in the connector plug real close make sure some are not pushed out. Had to remove one on a radio and spread so they would lock properly. The radio was interment.