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How to downgrade CASIO Prizm fx-CG20?

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How to downgrade CASIO Prizm fx-CG20?

Unread postby SuperXX » 09 Jun 2021, 22:04

Hi,

I´m trying to downgrade a CASIO Prizm calculator but I can´t seem to find an answer for it. I saw somewhere that by pressing the F2-4-AC/ON and Restart once the calculator was turned off, I would be prompt to a black screen so I then I would press 9 and install the OS. But nothing happens. Currently the calculator is in version 3.1.02

Thank you in advance
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Re: How to downgrade CASIO Prizm fx-CG20?

Unread postby critor » 09 Jun 2021, 22:08

Hi.

You just need to put the calculator in "OS error" mode using the F2-4-AC combo, and it'll then accept any OS version.

The combo is just very tricky :
  • press and hold the
    restart
    button on the back
  • without releasing it, press and hold the
    F2
    4
    AC
    keys
  • without releasing these 3 keys, release the
    restart
    button
  • now only release the
    F2
    4
    keys together
  • wait a second
  • now finally release the
    AC
    key
  • press and hold the
    9
    key
  • wait a second
  • release the
    9
    key
  • press and hold the
    ×
    key
    You should now get the OS ERROR screen.
  • release the
    ×
    key
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Re: How to downgrade CASIO Prizm fx-CG20?

Unread postby SuperXX » 10 Jun 2021, 08:21

It worked. Thank You. I didn´t have the correct key combination
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