Your F3 set is from the same era as my Milwaukee F3 AB, 6-18140, that I had TMCC and sound issues with. I reported it here but never got any answers.
I ended up replacing both boards (sound and receiver/tmcc) in the B unit and that corrected my problems except for:
B unit coupler doesn't operate
B unit back up light is on all the time
And yes I did a reset function multiple times but it didn't fix anything. I have all the "Lionel Parts Lists and Exploded Diagrams" published during that time frame. Supplement 43 has my Milw 6-18140 in it but there is no overall wiring diagram of the B unit included. So I can't determine if the coupler or back up light is connected properly in the wiring harnesses.
I'm beginning to think those old sound RS boards and tmcc boards deteriorate with age and there's not much that can be done about it.
Ken