I’ve done everything I can think of to get the most solid connection possible with those connectors. Mine is from the original shipment; have you made any design changes to that to improve the connection solidity?
I’ll check again…
I have reseated the power wires after doing everything I can for a solid connection. My latest test seemed more solid, but this time, rather than the symptoms of the overvoltage connection, it got 2 or 3 letters into the text when it just stopped moving for a few seconds as commands were sent over, then lost it’s position.
Better (I think) but still not workable 
Tried the sign again, using code from Vectric Desktop rather than FreeCad, and it worked just fine.
I need to try a few more experiments before I’m completely confident, but this is significant progress 
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Are you thinking it is CAD software related now because Vectric worked the last time? That would be good to know.
I believe it ultimately was related to the power connector. I reconnected the power connector to the line from the brick and it’s been stable ever since. I still regard it as a weak point in the design, no matter how industry-standard it is.
Thanks for checking!
Frank