There are two methods for doing this and they are as follows.
Firstly enable Telnet access by going to http://routeraddress/cgi-bin/sharedband.cgi?z=telnet.html in a browser whilst connected to the router, where the router address is the IP address of the router.
You should now be able to access the router by telnetting to the IP address on port 23 or SSH on port 22.
Once you are in the router type the following commands:
You should then see the following output from the router:
/sbin/sysupgrade: eval: line 1: opkg: not found
Saving config files…
killall: watchdog: no process killed
Sending TERM to remaining processes … sb_run memcheck sb_monitor ntpd sb_router sb_ router sb_router udhcpd sleep sleep ubusd askfirst netifd httpd
Sending KILL to remaining processes … unused ask askfirst
Switching to ramdisk…
Performing system upgrade…
Writing from <stdin> to firmware … [w]
Once the router has rebooted you will be able to access it using the default IP address of 192.168.0.1.
Set up a TFTP server on a machine with the IP 192.168.0.66.
Download the latest available firmware from TP-Link.
Use a HEX editor to remove the first 0x020200 bytes of the binary file.
Save the file to the root directory of your TFTP server and name the file wdr3600v1_tp_recovery.bin
Switch off the router.
Connect a LAN port of the router to your TFTP server machine.
Hold down the reset button on the back of the router and switch it on.
Release the reset button as soon as the LAN light starts flashing.
The router will eventually reboot itself and after this has happened you will be able to access the router on the default IP address 192.168.0.1.