I flashed preloader.bin and uboot.fip and after reboot the router is dead, no power light, no signal on Rj45 or USB , the router is completely dead. That's how your router is too?
I have not connected TTL serial cable but your case give me hope mine can be recovered.
Anyway, I guess in this situation the only solution is to flash the NAND. Never did that but as an electrical engineer I think I can learn.
Can someone suggest me tutorial and a ch341a programmer on AliExpress to use with the suggested cable above?
https://a.aliexpress.com/_mLgq4JI
Or any other AliExpress product to flash the NAND the easiest way and without soldering involved?