Sounds like you are talking about the pots which adjust your voltages.  Not really something you should fiddle with.  You should probably check the volatges now with a multimeter to make sure they are OK and not too far out of spec.

thanks for your helpful advice. the problem was simply the two blue round knobs on the system one power supply. turning those knobs corrected the display. i must have move them accidently. does this makes sense to you?

not sure whether those knobs are for brightness of display or do something else?

thanks again