[Fire TV Original Android Development] Androoit:
I already thought about soldering a switch(maybe smd variant that would fit good in the design) in with some short cables and drill a hole in the case and mount it there for easy access shorting the pin to ground if something goes wrong again (what happend a lot as i was experimenting with the stick) For dissasembeling reasons i should if i do so use some kind of small connectors inside to be able to remove the switch without soldering it off :unsure:

For the black/white screen: I had this too i dont remember what exact reason it was but my solution was to complete wiping the stick wiping all partitions in TWRP and install a stock Update.zip(renamed .bin update from the xda thread with original mantis cloudfront images) however i had no personal data on it so no loss. After a reboot it took its regular time setting it up on the first start with empty Cache&Dalvik and then it worked fine normal again.

I experience a problem too, when i try to restore a backup made from another Stick. My solution currently to get a working stick with my preset of Apks, Settings, OTA update off, wifi network is: Restore Backup with TWRP(System, Data)>Install Stock Rom.zip of the same version(Stock Rom overwrites System Image and Vendor Image partition) > all other stuff i want like patched kernel then magisk and selinux modul(for the kernel) + Mount script for NTFS, exfat, EXT4

>Wipe Cache&Dalvik > Reboot

And it works but one thing is annoying, on the first start the stick asks me to login to my amazon account(from the Stick i took the backup off). Once its done its usable as normal. However it takes a bit time navigating the screens until the Apps show off correctly. But thats only a matter of a few minutes of work. But then its perfectly working. I use fresh Sticks which never have seen its inital Launcher before. I strictly go to TWRP and use the backup + Stock image.

If i restore Vendor and Vendor Image the stick doesnt boot anymore, full wiping it and install Stock .zip brings it back to life and full working state. I wonder because Vendor should store the MAC, right? Maybe the update file from Amazon is foolproof so it generates the specific device code, i dont know. Im not experienced yet with Mediatek based Devices i usually rooted and flashed Samsung smartphones. I only flashed one Mediatek smartphone yet so im not aware of how it handles things differently. I know on Samsung when you dont take a Backup of NVDATA/NVRAM and it gets broken by a mistake you might be sitting there with a device without working wifi and cellular.

I didnt managed it yet to get the Stick into a non-recoverable state even i tried to test the borders of what is possible. Always was able to recover it(sometimes using kamakiri) no matter what i tried. I had also on different sticks updated to 6.2.7.7 user 3027 regular OTA update but i was always able to use a stock image flash it via TWRP and get back to another Fire OS Version. Also didnt experienced a efuse yet, but i didnt looked out for it anyway.

I wonder how i can set up a working Backup thats interchangeble between different 4k Mantis Sticks. I use Fire OS 6.2.7.7 user 3025 btw.