just now I left running for perhaps 2-3 maybe 5 minutes at most, screen went dark.
after a few minutes board works fine again.
I tested unit a number of times, everything worked as expected: ie square wave probe calibration
I am using 12v dc rather than 9v but according to documentation this is acceptable.
many report using 12v for days with no problems: https://www.muffwiggler.com/forum/viewt ... cad113c07c
I had assembled genuine unit, as confirmed by you, over last three days.