With the calculator off, hold down the [ON] key and press [X], then release the [ON] key. The calculator should show a flashing "running" for 15 seconds or so and then display -8,8,8,8,8,8,8,8,8,8, with all the status indicators turned on. If you see Error 9 or a blank display, or indicators are missing, the calculator will need fixing.
You can test the keyboard by holding the [ON] key and pressing [divide] then releasing the [ON] key. A pattern appears in the display; now you press each key in turn, starting with the top row and going from left to right, then the next row down, and so on (press the Enter key twice - once for each of the bottom two rows). At the end of the process, the display should show '16'. If you press a key out of order, you'll see 'Error 9'.
Best,
--- Les [http://www.lesbell.com.au]