How to mend keys on Seiko Oxford Crossword solver

Einleitung

The Seiko Oxford Crossword solver model ER3500 had some keys on the qwerty keyboard that often did not work. These were the most common keys (including the on/off) making it almost impossible to use.

The back of the device was opened to reveal the back on the key pads. These pads contain a black conductor (see image) and when pressed onto the circuit board complete a circuit to register that the key has been pressed. However on the frequently used keys, the black coating was no longer conductive.

To make the keys conductive again, some aluminium foil was glued onto them (see image) and the device worked again.

The device was still working two years after the repair.

Schritt 1 Dissasembly detail.

How to mend keys on Seiko Oxford Crossword solver, Dissasembly detail.: Schritt 1, Bild 1 von 3

How to mend keys on Seiko Oxford Crossword solver, Dissasembly detail.: Schritt 1, Bild 2 von 3

How to mend keys on Seiko Oxford Crossword solver, Dissasembly detail.: Schritt 1, Bild 3 von 3

Remove battery cover screw and batteries. Then remove 7 screws from rear. Prise the back and front covers apart using a blunt knife or similar. This requires a bit of force as there are internal plastic clips (one might break but it's not important). The only fragile thing is the glass LCD display.
Take care as the two casing halves are attached with two soldered battery wires.They can be positioned so that they are not stretched. (first image)
Remove 10 screws from the green printed circuit board to gently detach it (second image). The flexible rubber keypad can now be pulled away for repair.
On the back of the rubber keyboard are black conductive discs. The faulty ones can be covered with aluminium foil. (third image).
reassembly is reverse of above.