I want to JB my KOA1 fw5.12.2,serach and read some post in this forum, got info: that is impossible! But I did not give up
downloaded two "bin" files
update_KOA_5.7.4_initial.bin(from mobileread forums)
and
update_kindle_oasis_5.9.7.bin(from amazon official page)
tried to downgrade my KOA1 FW from 5.12.2 to 5.7.4 or 5.7.9,
of course it does not work, I copied "update_kindle_oasis_5.9.7.bin" to kindle, and : Home -> Menu -> Settings -> Menu -> Update, popup error say, "...update file is wrong...", system directly delete the file"update_kindle_oasis_5.9.7.bin", kindle won't start update process.
then I tried something else, copy "update_KOA_5.7.4_initial.bin" to kindle, do NOT unplug usb cable, directly press power button and hold for 20 sceonds, KOA1 reboot, popup info"...kindle is update...please wait....", after half a minute, popup "...update is not successful ...error code is 15..."
I did same process for "update_kindle_oasis_5.9.7.bin",my kindle try to update FW, but faild, "...error code is 12..."
what that mean: when user copy update "bin" file to kindle, and do not unplug usb cable, and press power button for 20 sceonds, hard reboot kindle, kindle will try to run the "bin" file, of cause the file can not pass some kinde pre-check,popup error code.
that means, in above process, kindle try to execute user "bin" file, maybe someone in this forum can customizes a "bin" file, tricks the fw5.12.2 system, bypasses the pre-check, JB kindle system？