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[RobJDean185]

In a separate thread someone got me sorted out with resolving a problem where battery fluid had shorted out the key pad but I had to disassemble the calculator to clean it. Since I couldn't find anything on YouTube or similar, here's a set of instructions for taking the Casio fx9860-GII apart.

 

This disassembly, cleaning and reassembly requires:

• Small (size 2.0 and/or 2.5) cross-head screwdrivers
• A small plastic pry tool
• A small (size 1.0 or similar) flat-head screwdriver or other pick tool
• Electronic/optical non-residue cleaning fluid suitable for use on plastics and electronics
• Cotton buds
• Soft, lint-free cloth
• Rubber solution glue (if replacing the screw cover plugs)

With all the usual caveats about taking care, warranties will be voided, and so on, these steps worked for me.

1. Put some light adhesive tape over all the keys and rub on firmly to avoid all the keys falling out during the disassembly. https://flic.kr/p/YfQPWU
2. Remove the battery cover to expose one screw in the middle section. Around the edge are six further screws. If these are covered by a soft rubber plug, use a very small flat screwdriver or similar to pry it out gently - it is glued in with a rubber solution glue. Make sure to store the screws safely and note that the two screws in the mid-section are longer than the others. https://flic.kr/p/YfQQLE
3. Gently pry up the front cover working initially from the display end. The fit is not too tight and it should be possible to lift away with fingers only. If it seems stiff or resists, don't pull hard but use a plastic pry tool to gently ease the front cover sides away from the black back cover. Once the front cover starts to lift away, turn the calculator over and use a fingernail to press out on the tabs securing the front panel to the back cover (highlighted on the right of the photo). The front panel should then lift off. Place it down carefully to avoid dislodging the keys. https://flic.kr/p/YRZdDB
4. With the front panel off the grey key contact mat is visible. This just lifts off, noting that the holes in the mat line up with the silver screws underneath and there is a small protruding lug (circled yellow) to help locate it more precisely. https://flic.kr/p/YfQQxo
5. Unscrew the five small silver screws that secure the display (three screws) and keyboard to the back panel. There are a couple of plastic lugs holding the keyboard in place but the keyboard should just lift away from these. See the next picture for a note about actually lifting out the display and keyboard. https://flic.kr/p/YfQQjs
6. With the screws removed, the keyboard and display should lift out of the back panel together. Some care is required because the keyboard has the main battery contacts on it and these have to be eased out of the back panel carefully. Both the display board and the keyboard come out together joined by the ribbon cable between them (see next photo) - do not bend the ribbon cable too much to avoid risking any of the soldered contacts. Note that only the two highlighted battery contacts come out with the keyboard, and that when re-assembling them, they must slide back in to the plastic grooves properly (the widest parts of the positive/flat circle and negative/spring cone). Do not force the keyboard in to the back panel - it requires a little manipulation to line everything up but they should fit back together smoothly. https://flic.kr/p/YRZcgr
7. Once removed there are two circuit boards, one for the keyboard and one for the display. The photo shows the reverse side and highlights the two battery contacts plus the ribbon cable between the two circuit boards. Clean off any dust or contaminants with a suitable electronic cleaning fluid or spray. Battery leaks will contaminate the side shown but may get through to the contact side of the keyboard as well. If contamination is significant then look out for accumulation under the folds of the ribbon cable. The exposed soldered contacts for the ribbon cable should also be check in case there is any contamination which may short circuit them. Take the usual precautions about static and don't be too vigorous with cleaning where there are small components or protruding wires. https://flic.kr/p/YfQR1h
8. After re-inserting the display and keyboard in to the back panel, check that the battery contacts are properly fitted to the slots in the back panel. If necessary clean (suitable non-residue cleaner) the black contact faces on the key contact mat (the photo shows the opposite side - the contact faces are the black pads underneath), then replace the key contact mat and the five silver screws on the main keyboard - do not over tighten the screws as they will strip the plastic thread. Make sure the key contact mat is properly oriented and located on the protruding plastic lug. Once the five screws are replaced, the ones on the keyboard should be visible through the holes in the key contact mat. https://flic.kr/p/YfQRaq
9. Relocate the bottom end of the front panel so the tabs fit to the back panel properly, then gently press the front panel back in to place, making sure not to dislodge any keys as this happens. After the front panel is on, turn the calculator over and replace the seven screws holding the back panel to the front panel. The mid-section screws are the two slightly longer ones and in all cases do not over tighten the screws as they will strip the plastic thread. If you are putting the foam plugs back in use a light rubber glue or something similar so you can get them out again if necessary. https://flic.kr/p/YRZeBi

Good luck.