Here’s how to recode your Tritronics collars if the receiver quits responding to the transmitter. I’ve used on my Pro 200 XLS and Sport 60. This information was sent to me by Tritronics in June, 2007.
1. Have all system components together (Transmitter, receiver, and wall charger).
2. Prepare the receiver unit to accept the code by turning it on and then off again (this is called cycling the unit).
3. Set the transmitter to a number (1 would be fine).
These next steps are very time specific and they must be done in a smooth sequence as you will only have approximately 2-3 seconds between stops – once you start the sequence don’t stop or pause.
4. Plug in the charger into the electrical plug with nothing on the leads (no collar or transmitter).
5. Plug the receiver into the charger, almost simultaneously you were hear a beep.
6. Press the activation button on the receive (within 2 seconds of hearing the first beep); when done correctly you hear another beep.
7. Hit the red button on the transmitter (again within 2-3 seconds) and you should hear a third and final beep.
8. Take the collar off the charger, turn it on and see if the red light on the front of the receiver now goes on in time with your pressing the red stimulation button.
If it does then you have successfully recoded the system.
If not, or if you do not hear all three beeps, cycle the unit (step 2) again and repeat steps 5-7.

Thanks! I've long since lost my original directions and I'm sure at some point, this will come in handy!