I have two TX1’s. One purchased a year ago, another just a couple months ago. Both have serial cables connected to UART0 on the J21 header. My newer TX1 will boot but the older one won’t, unless I remove the serial cable. The lights turn on but I cannot ping it and no display shows.
I have read the posts about editing U-boot but I have not done anything like this on my newer TX1, and I am not sending anything on UART0, only listening for the boot messages.