my final update on this one:
the replacement monitor started to flicker on 120hz after 2 weeks of use, Acer customer service told me it's a firmware issue and I have to send it to the repair centre = minimum 2 weeks without monitor and there is zero guaranty it will work or be back undamaged. Oh i don't thinks so. If it's just a firmware anyone could do it.
I#m done with Acer .. what a shambolic company. Now I understand why everyone say @buy from Dell@