Help bring DS420j to life

[b72nja01]

Hi all. I have DS420j which is not booting after installing OS. 

The operating system installs without errors, then the device says that it needs to reboot and turns on the timer for 10 minutes in the web interface.
After this time, the web interface writes that something went wrong. If I reboot by turning off the power, after loading it says that the operating system needs to be reinstalled.
I connected via the serial console, the device constantly gives an error: "usb usb5-port1: Cannot enable. Maybe the USB cable is bad?" Based on the symptoms, it looks like the bootable flash has died. The problem is that in my case it is soldered onto the board.
After reviewing a bunch of posts on the Internet, I decided that I had found a solution - find a USB flash drive, change “VID” and “PID” to F400 on it, find a synoboot image somewhere and load it onto the flash drive then boot from it. Unfortunately, I failed - when I logged into the same working machine via SSH, I did not see synoboot in /dev.
What other recovery options are possible?