[Fire HD 8 and HD 10 Original Android Development] Jik Sey:
I have put together quick guide to unbricking the 8th gen Fire HD8 (karnak) stuck on the white Amazon logo, without having to take the back off or having to short any wires. I hope this will help someone out if they are stuck on what to do next. This is based on other great posts by By k4y0z & xyz & Xinto & Scripts used amonet-karnak-v3.0.1.zip and brick-karnak.zip

I am assuming that you are already using a Linux installation or live-system running ADB and have the amonet-karnak-v3.0.1.zip and brick-karnak.zip extracted to have bricked your tablet in the first place :) I am basically a total newbie but I have now tried this 3 times on 2 8th gen Fire HD8's (karnak) tablets with differing Firmware that were stuck on the boot logo. Please note I am not responsible of any physical damage in your tablet, if you choose to make these modifications.

1. First power off the tablet (Hold power button down for 20 seconds until the Amazon logo disappears)

2. Hold down the left Volume button, while pressing the Power on button. Then Plug the tablet back in.

3. From inside the brick-karnak/amonet folder open a new terminal and TYPE

sudo ./brick.sh

The terminal will say ...Brick preloader to continue via bootrom-exploit? (Type "YES" to continue)

4. Make sure you type YES, not just y or yes like I made the mistake of doing a few times!

The terminal will then say

Bricking PL Header

Check instructions on device

target reported max download size of 114294784 bytes

Sending 'brick' (111957 KB)...

OKAY [ 3.886s]

Writing 'brick'...

On the Amazon Fire screen it will display.... All good now unplug and power off the device.

5. Unplug the tablet and power it off (Hold power button down for 20 seconds)

6. From inside the amonet-karnak-v3.0.1/amonet open a new terminal and TYPE

sudo ./bootrom-step.sh

The terminal will say .... Waiting for bootrom

7. Plug the tablet back in and the Terminal will say something like

found port = /dev/ttyACM0

[2019-12-26 21:09:53.550179] Handshake

* * * If you have a short attached, remove it now * * *

* * * Press Enter to continue * * *

8. Press the Enter Key

The Terminal will say something like

[2019-12-26 21:10:00.564737] Init crypto engine

[2019-12-26 21:10:00.580769] Disable caches

[2019-12-26 21:10:00.581253] Disable bootrom range checks

[2019-12-26 21:10:00.622439] Load payload from ../brom-payload/build/payload.bin = 0x4888 bytes

[2019-12-26 21:10:00.626302] Send payload

[2019-12-26 21:10:01.261823] Let's rock

etc, etc, until.....

[2019-12-26 21:12:56.277773] Reboot

9. Unplug the tablet again

10. From inside the amonet-karnak-v3.0.1/amonet folder open a new terminal and TYPE

sudo ./fastboot-step.sh

The Terminal will say < waiting for any device >

11. Plug the tablet back in

The Terminal will say something like target reported max download size of 114294784 bytes

sending 'recovery' (13604 KB)...

OKAY [ 0.474s]

writing 'recovery'...

OKAY [ 0.619s]

finished. total time: 1.093s

target reported max download size of 114294784 bytes

sending 'MISC' (0 KB)...

OKAY [ 0.012s]

writing 'MISC'...

OKAY [ 0.006s]

finished. total time: 0.018s

rebooting...

finished. total time: 0.052s

Your device will now reboot into TWRP.

Now your tablet will now reboot back into TWRP recovery ready for action.