Lionel 6-18064 Mohawk ACDR board

One thing I have seen- does the 4 pin cable have all 4 wires? The reason is, I have seen where the 2 directional inputs are not common together- so you have a signal- but no return path from the opto-isolator input. This diagram shows- that "common" is actually the 5V source, and the signals are GND reference and thus current sinking.

Again, I could be wrong but I think I have seen this before, and was either a 3 wire cable was used- and the ACDR board did not connect or bridge both 5V pins on this interface- leading to basically a 1 wire situation for that direction.

Have you tried remelting the solder on the triacs?

I'm surprised those boards are still available from Lionel!  Most of the TMCC boards are long gone!

It’s a 4 wire harness and I have continuity between the R2LC board, threough the motherboard to the ACDR board.  I resoldered the pins on the motherboard, but the ACDR boards are supposed to be new.

I've gotten quite a few bad parts from Lionel, it happens.