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Casio fx-CP400 Keypad Cleaning

Introduction

The keypad of the Casio Classpad II (fx-CP400) may require some cleaning between the rubber dome switches and PCB. Use this guide to disassemble and clean the keypad.

What you need

  1. Casio fx-CP400 Keypad Cleaning, Casio fx-CP400 Keypad Cleaning: step 1, image 1 of 1

    • Remove the batteries and battery cover.

    • The "UNLOCK" slider should extend out the side of the calculator in the open position.

    • The battery cover hinges from the bottom and can be lifted out.

    • Remove the 6 Phillips head screws from the back of the calculator.

    • 4 of the screws are behind the battery cover.

    Edit

  2. Casio fx-CP400 Keypad Cleaning: step 2, image 1 of 2 Casio fx-CP400 Keypad Cleaning: step 2, image 2 of 2

    • Two plastic clips hold the black front plate (keypad and screen) into the white frame around the calculator. The back plate (battery holder) is screwed into the white frame internally.

    • Start with the left side of the calculator:

    • Wedge a plastic opening tool into the bottom of the calculator (where the keypad is) and slide it up to the clip (see photos).

    • You may use a credit card or guitar pick for this step.

    • Push the clip in and pull the front plate away from the white frame.

    • The blue band around the front plate may either lift with the front plate or stay in the white frame. It does not matter.

    • Repeat for the right side of the calculator.

    • Carefully remove the front plate from the white frame of the calculator.

    Edit

  4. Casio fx-CP400 Keypad Cleaning: step 3, image 1 of 1

    • Remove the 2 Phillips head screws holding the keypad PCB to the front plate of the calculator.

    Edit

  5. Casio fx-CP400 Keypad Cleaning: step 4, image 1 of 2 Casio fx-CP400 Keypad Cleaning: step 4, image 2 of 2

    • Lift the keypad PCB and remove the rubber membrane.

    • Clean the bottom of the keypad PCB with alcohol wipes and dry thoroughly with cotton swabs.

    • Similarly clean the black contacts on the rubber membrane.

    Edit

    • Reassemble the calculator by following this guide in reverse.

    • When screwing in the keypad PCB, elevate the keypad to ensure the keys are not pushed in as this will prevent the PCB from seating properly.

    Edit
Finish Line

Author

Sskki

Member since: 03/20/26

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