Tommy
Hello & Welcome to the Forum!
I haven't been able to locate a schematic for your "818-5000-040 Circuit Board RailSounds" but the Lionel Parts & Service Department may have one available.
If not, your Elec. Engr. friend should be able to reverse engineer your board and you can go from there.
Happy Rails!
Dave
Thanks, Dave! I'll contact Lionel Service/Parts.
Tom