71B: repair/polish LCD screen scratches

[Hans Brueggemann]

fortunately, the HP-71B has an extra perspex insert in the display frame that protects the underlying LCD from polishing "accidents". the perspex has a thickness of approx. 1 mm. that should give plenty of margin for buffing out any scratches.

one trick i tried in the past with admittedly so-so success was to fill out a deep scratch with a drop of transparent UV-curable resin (comes in small bottles with a blue LED keyfob as UV-lighsource) first, then wet grinding it down to 2000 grit, and then manually polishing it with acrylic polish. don't use power tools as they might burn the perspex surface because of too high rpm.