NSA325v2 How to write U-Boot by JTAG to NAND (no replies)

Hi,

After flashing by RS232 my Zyxel is dead. Not booting and RS232 not working, only reseting after 30 sec.
Unbrick method by USB not working.
How to connect JTAG to pcb (pinout) and write u-boot ?

Thanks for Your help