Review on DTECH USB to TTL Serial Adapter Cable 4 Pin 0.1 inch TX RX Signal with PL2303 Prolific Chip (6ft, Black): Windows 10 8 7 XP Vista Compatible by Ryan Whatley

cable worked exactly as advertised. Connect the cable to the JTAG connector on the R8000 motherboard according to the pinout shown (don't forget to use a T10 Torx bit to open the case). DO NOT connect the red wire to anything as it will provide USB power to the port and fry it. I plugged the USB end into my Ubuntu laptop and checked dmesg to find the port name, which was /dev/ttyUSB0 by default. I opened PuTTY (as root - you can only access this port when PuTTY is running as root) and selected Serial, added the port and set 115200 as the speed. As soon as the R8000 was powered on, the serial port showed the router's console view, including the entire boot sequence. By interrupting the startup sequence with Ctrl-C, I was able to type "tftpd" to start the TFTP daemon. I then started tftp from a command prompt on the laptop, switched to binary transmission and connected via ethernet to 192.168.1.1 which is connected to one of the R8000's LAN ports. I put the factory image back on the router, and after a reset 30-30-30 it was up and running again.