Add a custom background to a Casio F-91W

Lay the watch face-down on a clean cloth. Use a Phillips #000 screwdriver to loosen the four caseback screws, leaving each screw sitting in its hole until all four are free. Lift the screws into your tray, then remove the steel caseback.

Lift the black rubber gasket away with tweezers and set it somewhere clean. Do not stretch it. Hook a fingernail or plastic-tipped tweezers under the edge of the module and lift it straight out of the case.

The metal battery plate clips around the white LCD carrier at four points. Put a small flat-head screwdriver under one clip at a time, then twist gently and push outward. After the third clip releases, the fourth may come free by itself.

Lift away the battery plate and circuit board as one assembly. Watch for the small striped rubber connector between the board and LCD. This conductive strip is what carries power and signals to the display; keep it clean, do not squash it, and do not lose it.

Release the small latch at the bottom of the white carrier and lift the glass LCD out. Note the three tiny dots at one edge of the glass. When the display is facing you during reassembly, those dots belong on the left.

Turn the LCD over so the silver backing faces you. Several films are laminated to the glass; you only want the uppermost silver, adhesive-backed reflector. Starting at one corner, use the very tip of a fresh hobby blade to lift that layer. Keep the blade almost parallel to the glass and pry upward rather than scraping across it.

Once there is enough film to grip, put the knife down and peel the reflector away slowly with your fingers. It takes a little force. Stop if another clear layer begins to lift with it: removing the polariser will stop the LCD from displaying normally.

Wipe both sides of the glass with a clean microfibre cloth. After the silver film is gone the front and back look similar, so use the three dots—not memory—to orient it.

Place the trimmed artwork face-up in the back of the white carrier. Set the LCD over it with the three dots on the left when viewed from the front, slide the glass fully into position, and close the lower retaining latch.

Turn the carrier over and return the striped rubber connector to its channel. Lower the circuit board into place, aligning its notches and metal contacts with the carrier. Fit the metal battery plate over the board and press around its edge until all four clips click home.

If the display remains blank, perform the module’s AC reset: briefly bridge the contact marked AC to the battery-positive metalwork with metal tweezers or a paper clip. Remove the bridge as soon as the digits appear.

Blow dust from the inside of the crystal, the display and the artwork. Any speck left now will be trapped in the most visible part of the watch.

Check that all three external pushers are sitting fully outward. Lower the module into the case and gently press its spring contacts inward as they pass the pushers. The module should sit flat without force. Test the time, mode and light buttons before closing the case.

Lay the rubber gasket back into its channel. Follow it all the way around with a loupe or your fingertip and make sure it is flat, untwisted and not caught under the module.

Fit the caseback in its original orientation and start all four screws by hand. Tighten them gradually in a diagonal X pattern so the back and gasket settle evenly. They only need to be snug; overtightening can strip the resin case.

Give the display and all three buttons one final check. The image will look darker through the LCD than it did on paper, but it should sit flat, fill the window and remain clear of the digits.