So, additional question: Intermittently, Chain 1 has shown up with all xxxxx, or with 1 chip x'd. Disconnecting the ribbon cable was a real mother*ucker - could damage to the control cable account for that? Again, it's intermittent. Power cycling will result in one of those error states, or a non-error state. It seems that if I power down and "fiddle" with the cable, it comes back up in the non-error state.

So, that's a point for the DIYers on the S7-LN - it would be better to remove the power supply and have plenty of room to work the control cable off while supporting the socket to ensure you don't damage the cable or the socket.