Not so much a repair as just documenting this incase others run into the same issue...
So the IT8512+ (firmware v1.12) can do 120V, well at some point mine decided not to go above 18V OR 18W, CC worked fine to max 30A, but CV/CW would not go over '18'.
Thought that was a bit strange, tore it down, tested loads of things, nothing. put it back together and still the same...
So, I was annoyed at the constant 'beep' pressing keys so I turned the beep off and saved it as configuration0 or save0, and had that load when the machine turns on...
well, I changed it to reset when it loads, problem solved. just gotta live with the annoying beep.
somehow its internal stored settings/calibration? had been corrupted as telling it to use defaults on load fixed it.