TMCC not working

Do you have the base connected to a good known grounded outlet.

The first question - did you connect the TMCC base ground wire to the outside rail of the track? As you may remember, TMCC needs both the over the air signal you see on your 'scope AND the TMCC base connected to the outside rail "acting" as return for TMCC signal.

Was the antenna you used with the 'scope held over the track, or at some distance from the track? If some distance from the track, try the extension cord test where you plug TMCC base in a 3 wire extension cord (so it has earth ground), then plug extension cord into wall, and lay extension cord next to track. As you might guess, this gets the TMCC antenna as close to the track as possible.

Hope you find it was the TMCC base ground to outside rail of the track.

I did have the base power plugged into a 3 wire extension.  My first attempts were with track some distance from the transformer with the TMCC base wire to a U terminal on a ZW.  I then went to another spot with the transformer and TMCC base closer to the track.  In both cases the F3 recognized the presence of the TMCC base signal, but no response from any commands.

TMCC base ground wire to U on ZW will work IF all four U connectors are still bussed together. It is not uncommon for one or more of the U connectors to become disconnected from the metal bus inside the ZW that is supposed to connect all four U connectors together. Suggest doing a test by running TMCC base ground wire directly to track outside rail. If this works, you can turn off ZW and use ohm meter to check that U connectors are all still bussed together inside the ZW.