dave wrote:
i'm working on a plane and his RT459A transponder is not working properly.
I would suspect that it may be cheaper to replace than to fix it.

Are all the ARC transponders interchangeable?

AFIK, RT359A and RT459A are slide-in interchangable. All are actually
14V with a dropping resistor on the tray in 28V installations.

If not, which ones are/aren't?

?

Are there any replacement transponders that will fit the tray?

Not AFIK.

MikeM
Skylane '1mm (which has a working RT359 with a RT459 back up on the shelf)