There are many ways to brick this HU and numerous firmware and firmware bits scattered all over. Some are even inaccessible. Backup provides an option for recovery.
Fortunately, we have developed a simple backup tool that everyone can use. Read System backup below.
Read here
xyauto has removed access to their file server to find firmware for recovery. xyauto firmware also DO NOT contain some files which need to be retrieved from backup process.
To just backup the system ( no user data or user installed apps, just the default HU firmware system ), it is quite simple. Backing up complete user installed app and user data is more complex. System backup is sufficient to recover bricked HUs so everyone should do this. And its very simple.
Take a picture of this. It will tell HW model. basic specs, and firmware type and version. Useful for recovery later. See "Car Settings" tab.
If need to restore HU firmware later, IMEI info will be erased. This require disassemble HU to read the IMEI # on logic board stickers. Use Android settings to find and save IMEI
Read here
To do a PC flash, firmware require 3 key files to combine with xyauto's PC flash firmware.
preloader ( never change so its archived in the MEGA repository link Can ignore this until need to recover from backup later. )
metazone ( retrieve from the HU using backup method below )
logo ( many versions exist, wrong one will display brick HU, restrive from the HU using backup method below )
@achushatz developed a simple ota tool to extract metazone and logo (along with all other files to recover the system in case of bricking). This greatly simplifies the extraction AND backup process
Tool is located in post #4286. Just put on USB stick like other ota updates.
After tool is finished, complete dump is located in xyauto directory on the HU. Copy this directory to USB stick to save it. If you leave it on the HU and flash the HU, it could be erased, and backup is lost.
If intending to use these files as a backup. Also note the firmware version (to find the matching scatter file, see post #4377 link below)
Note this tool doesn't dump user installed apps or data so they will potentially be lost when flashing new firmware.
Note this tool has been tested in 1.80.1 2G 32G horizontal 5760B HU ( post #4377 ) and 1.75.* 5760D ( post #4489 ) so seems quite robust. Post also shows where to find other files necessary to recover the HU with this firmware dump. Should find and store all the files in safe location (not on HU) for potential recovery need)
Of course need to recover a few settings after an "ota update" See here ( link )
After completing saving and backup steps above here. You have everything to recover a bricked HU so its safe to flash the HU. But make sure you saved and backup everything in the "Why backup" section above here.
To recover HU with above ota backup tool, follow post #4427
There are more complex backup processes and can backup complete user installed apps and data in case you don't want to lose these. See Complex Backup. It is more difficult.
Read this before attempting to flash PC with even small updates
Android "Settings" -> "System" -> "About Car" (scroll down).
There should be 2 SIM slots (on-board SIM slot, external cable SIM slot), but both should have the same IMEI #.
IMEI #s are 14 digit + 1 digit checksum making total of 15 digits. You will need to paste in 14 digits on the Maui Meta tool after flashing new firmware via PC. It will compute the checksum.
Make text file looking like this:
IMEI 1
xxxxxxxxxxxxxxX
IMEI 2
xxxxxxxxxxxxxxX
14 x = IMEI, X = checksum
If IMEI already erased and unknown, it's written down on HU's logic board. Don't recall if SIM slot on logic board is underneath metal EMI cover and have separate IMEI sticker.
360 license will be recovered by network too, a dialog about license will appear and just click the "ok" button.
Be sure to backup 360 calibration data to U disk or SD card in the 360 application settings (password: 4321) before flashing, and recover it later.
Source: https://xdaforums.com/t/ac8259-cpu-based-hu-problems-questions-mainly-yt5760.4171219/post-88226989
See "Activation" chapter here, especially at the end.