I've got the 6-18876 CNW Fairbanks-Morse H12-44 with TMCC and Pullmor motor. The engine stopped responding to Horn/Bell and other sound commands in TMCC mode. They still sounded in conventional mode. I bought a new LCRU2 last month (Lionel parts sale) since I figured that was the issue (both are Rev. C). I expected to drop it in, reprogram the Engine ID# and the Engine Mode code and go, but nope. The brand new LCRU2 behaves only as if in Conventional mode, even though I'm controlling everything with my Cab-1L Base and Powermaster. Putting it in Program just makes it move as soon as power is applied with no neutral. I checked the antenna, no issues with the rails on the body or the connection inside. I even pulled all the Railsounds guts out to get it just down to the bare functions, but still no luck.
There's a component on the LCRU2 board in one corner, a boxy thing that has "COILS" stamped in it, some numbers printed on it, and clearly something inside that can be adjusted with a flat-blade. It seems to be labeled L1. I have never seen a description of what this is or does. Is this related to the TMCC signal receiver and might be the solution to my problem?
P.S. Thanks for those that helped me with my signal relay question. I've got something working now, really ugly, but working well.