is it possible to DOWNGRADE the firmware?

[danielmewes]

I had the same question today, and found a way to do it. The trick is to use the recovery mode to install the firmware.

Basically you follow instructions 1-4 from here:
http://h30434.www3.hp.com/t5/Calculators...-p/4391146

Then at step 5, you can use the connectivity kit instead of usbtool (using the connectivity kit I think might be safer).

Before you start the connectivity kit, make sure that you have the right firmware version that you want to downgrade to in the folder `C:\Users\yourUserName\Documents\HP Connectivity Kit\Firmware`. Just download the version you want from http://ftp.ftp.hp.com/pub/calculators/Prime/Archive/ and unpack it to that folder (delete everything else in that folder first).