Some boards do not have ports for flashing(debug ports), but you can still find the real circuit to attach TTL wires. Just need someone who understand router boards good enough.

For now, best thing you can do(like me), is to flash router with previous US firmware version - TL-ER604W(US)_V1_151021. (this firmware will report that router hardware is version 1.0. Only bad think...

I have same problem! Updated to wrong US v2 firmware version, and cannot back to v1. Also router have slow wi-fi and is getting slower and slower until reboot. This is not cheap router, but so slow...