The master TX is always "on" with antenna fully extended. The student slave TX is turned off. I'm pretty sure the slave TX has to be set in FM or PPM mode but the power should not have to be turned on. The antenna should be collapsed.

I have the older 6XAs TX with dedicated Futaba buddy box and the round to micro cord. The buddy box will NOT work if I am in PCM mode and with a PCM RX. As soon as I hit the trainer button on the 6X, the LEDs on the buddy box light up and it has control. The 6XAs was a bit odd in that everything had to be PPM mode. My 9C can be in PCM but the slave TX has to be PPM (and turned off).

Which "old" Futaba system are you using?