How to unbrick if U-Boot is still ok
This is the procedure if U-Boot is still running, but the Kernel and/or minifs in NAND flash are damaged so that you can't install the recovery image.
If U-Boot is no longer working, it is not possible to start the machine.
We are currently working on a procedure to open and disassemble the device and re-install U-Boot in the NAND flash through JTAG. Unfortunately, accessing the test connector needs really to disassemble everything. So this is not recommeded to do it yourself.