DO AT YOUR OWN RISK. I am not responsible for any damage or loss that you incur following the instructions or procedure explained below.
WRT1900AC Serial Port.
What do you need to login in serial mode to WRT1900AC?
Your PC or laptop running Windows or Linux with free USB or serial port
One serial to TTL USB or serial to TTL adapter Show
Putty software utility.
Philips screwdriver, medium size, don't need a picture ...
Unscrew the four bottom screws....Show
Pull the Blue Cover towards you....Show
Dismount the upper middle black cover....Show
Connect USB to TTL adapter to your PC and the cables to the white left side connector as described in these three pictures....Show....Show....Show ....Show
Power ON the router. Run Putty with settings 115200 baud, serial and you're connected to the router.....Show....Show