CASIO fx-4000P scientific calculator from 1986

[Csaba Tizedes]

(09-26-2018 07:16 AM)Csaba Tizedes Wrote:  Another question: the second unit is arrived this Monday and really like a new but as I can feel the bracket [(] [)] keys response is poorer than others. I will clean the unit inside, my question is between the keyboard foil and PCB is it required to clean or that will kill the contacts? Is it possible to clean the foil itself? What is the right cleaning liquid?

OK, the question is open: how to clean it inside without kill the contacts of the keys?

Thanks!
Cs.