My 12-year old Casio scientific calculator LCD stopped showing a couple of rows recently. After taking it apart, i found a flexible ribbon cable either glued or soldered to the edge of the PCB. As a first try, I heated the connection a little and it worked. Some slight finger-poking helped to find which part of the ribbon contact was faulty. I did not disconnect the ribbon completely, but simply warmed it up with a hot air soldering station at 120 degrees Celcius. Now the LCD is in order again.
Update: it has broken loose again, lasted 6 months :/