Paul and Roger - thank you very much for the very helpful information.
I've retrieved the schematic and had already obtained the user's manual
from the ICOM website. I'll study the schematic.

As for the tone generator, I'm planning on using an old laptop computer
and "nch tonegen", which is a software program that can generate an
arbitrary sinewave signal. The main task at hand is to isolate and
bring the appropriate connection point out to the back panel where I
can supply the tone on transmit.

Again, thank you both for your fine support!

73 Dave WB0GAZ