I have an existing system that has several 412 TDL boards in it. 2 of those boards have intermittent issues. I purchased 2 "working" boards from a reputable seller on Ebay to replace them. I tried the cards last night and neither one would work. All phones flashed the message waiting light but never booted. Popped the old cards back in and they booted fine. I have been working on Magix for @22 years but am I overlooking a potential software version handshake between these cards and the processor?
I am leaning toward faulty boards?

I'd also lean towards faulty boards, but first, with the old cards in place, do a backup to the PCMCIA card. Install the new boards, and do a Board Renumber. See if it works after that, if not put the old boards back in, see if it works, and if not restore from the backup and you should be in the same place as before any changes.

I too would think bad 412's.