Quote
uncle_bob
Quick fix on the board you have - put a pull up resistor on the output of the '125 chip.
If this is the same TX/RX that comes out on Digital pins 0 and 1, then IMO you could put a resistor on a female header and put it on Serial0 on the RAMPS-FD (between pins 1 and 4). This way is fairly non-invasive and easily removed if there is an issue or you get a new board.
That said, pretty poor that they don't actually have version numbers on their board. *sigh*
I too have the original model. In my case it came from LittleBird Electronics.