Laptop Display Screen Wobbles About.

Acer TravelMate 803LCi Laptop Notebook. Display-Screen Wobbles About.
I think this is a purely mechanical problem. On
opening the screen it is impossible to get it to
"lock" into any selected position (it flops back
and forth 3 to 4 inches around whatever position
is selected). It is a real nuisance - I had Acer
look at it and they seemed to have fixed it, but
the fault returned within a few weeks. I have
tried to tighten up the two small screws (hidden
beneath black rubber plugs)that push onto either
end of the hinge at the bottom of the screen, but
they are already tight. If anyone knows of
anything else that can be done then I'd certainly
appreciate hearing from you.