R6700 Bricked or corrupt FW after update (solid amber power light)

There's many steps in tftp that can have things go wrong. And it sometimes takes a couple tries. 

are you on windows? if so, follow this guide

https://kb.netgear.com/000059634/How-to-upload-firmware-to-a-NETGEAR-router-using-Windows-TFTP

just make sure you enable tftp 

https://www.thewindowsclub.com/enable-tftp-windows-10

and here's a video walk through. This can be key to helping. 

https://www.youtube.com/watch?v=R9DLrLQrpaw

and if that doesn't work, you can try using nmrpflash

https://github.com/jclehner/nmrpflash