SXT SA5 (AKA SXTG-5HPnD-SAr2)

I saw some discussion about this model and similar ones here.  It's a rather old thread, so I figured it would make more sense to start a new one here in development.  I think I could work through any model-specific problems if I could get it to boot, but I can't seem to get even that far.  There are pads on the board for UART, but they don't seem to be active during the TFTP boot process, so its difficult to determine where I'm failing.  I've had success ram-booting other Mikrotiks in the past.  I was hopeful that the development area would be an appropriate place to ask questions about hardware that is not or has yet to be supported by AREDN. If that's not appropriate I can try my luck on the Openwrt side and circle back around.