[7" Kindle Fire HD Android Development] galearned:
ChemicalM: Good day:

The work you performed installing 2nd bootloader and TWRP recovery did not fix your fatboot issue (Nor did it break it) as there is nothing wrong in the first place.

The 2nd gen Non-HD 10.46 firmware, and the HFHD7 7.4.6 firmware cannot get into fastboot by issuing any commands like those you see in adb or fastboot. The reason is the Kindle recovery OS is not designed to do this so it is not messed up or broken. Only the Kindle fire 1st gen 6.2.3 firmware and the KFHD8.9 have a recovery OS designed to respond to those commands. In the case of ADB reboot-bootloader for instance, when issued, the tablet will reboot but, the Kindle recovery OS is not designed to respond to the bootloader command and thus, will simply ignore it and boot up normally.

You did correctly see that after installing 2nd bootloader and,TWRP recovery, the reboot-bootloader commands now work. The reason is that the TWRP recovery OS supports those commands. The result is that you think this process just fixed something broken but, in fact just added a new feature albeit a feature the Kindle recovery OS should have had in the first place.

The Kindle fire stock recovery supports only two functions (Reset factory defaults and reboot nornally). Both functions are essentially the same command except reset clears all the user stuff first, then reboots the tablet.

Regards

---------- Post added at 11:24 AM ---------- Previous post was at 10:57 AM ----------

Peeptastic: Good day: Pointing out here that it is possible to re-install the Kindle OS once you have TWRP installed.

I am not sure in what TWRP version, reinstalling the Kindle update started working but I can report that if you are using TWRP 6.3.1, you can place the 7.4.6 Kindle update from the Amazon site on the tablet and flash it in TWRP successfully. I have re-installed the Kindle Update many times on numerous tablets and all have been successful.

Examples: with root and TWRP 6.3.1 installed:

Running Kindle OS 7.4.3 or probably any version:

Running Kindle OS 7.4.6:

Running custom ROM:

Place Kindle update 7.4.6 on sdcard with the .bin extension changed to .zip

Boot into TWRP, Wipe/swipe reset factory defaults (first screen option) then, back up and using the install tab, select kindle update 7.4.6.zip and wait until complete. The update will install 7.4.6, get rid of TWRP, root, etc. etc. and you are back to stock OS.

There was a time when this procedure did not work but, it now works well.

I did see where where root is kept (not sure from which original running version) which is good if you want to keep it.

If you do not want to keep root, then removing root is very easy without jumping through hoops.

Install Estrongs file explorer and using Estrongs settings/root options/general settings, set up r/w for system.

Move to the system folder/app and delete superuser.apk, then back up to system/xbin and delete su.

Root is now gone and icons are cleared out as well.

If for some reason, you do not have the right set up or, some odd thing occurs and the install does not complete, you can always use the fastboot cable and restore the OS using any one of the various restoral tools or manually flashing recovery, bootloader, boot, and or system partitions and get back to a working tablet (Page one of this post).

Regards