I was playing with this router till I bricked it. Following is the recovery procedure it worked for me, tested on Xubuntu 12.04.
Firstly set your lan interface to obtain a fixed IP in the subnet 192.168.1.x subnet, such as 192.168.1.10, netmask 255.255.255.0 as usual.
Download and extract the firmware with chk extension in a temporary directory.
Built a TTL cable to use the terminal through the internal connector JP1 which has this pin out:
Open a terminal emulator such as putty and configure the serial for a speed or 115200 baud and leave the other options set to default (8N1). On Xubuntu you can install it with a simple
sudo apt-get install putty
Enter the bootloader
Power cycle the router, press immediately and continuously CTRL+C to interrupt the bootloader and get the CFE prompt (this assumes you have the TTL serial adapter connected and ready to go)
Decompressing...done CFE for WNR3500Lv2 version: v1.0.9 Build Date: Fri May 6 11:54:17 CST 2011 Init Arena Init Devs. Boot partition size = 262144(0x40000) NFLASH Boot partition size = 524288(0x80000) et0: Broadcom BCM47XX 10/100/1000 Mbps Ethernet Controller 5.60.136 CPU type 0x19749: 480MHz Tot mem: 131072 KBytes Device eth0: hwaddr 74-44-01-33-BD-C2, ipaddr 192.168.1.1, mask 255.255.255.0 gateway not set, nameserver not set Startup canceled CFE> ^C CFE>
Clear the nvram, missing this operation is often the cause of bricked routers
CFE> nvram erase *** command status = 0 CFE> nvram commit *** command status = 0
Start the TFTP server
CFE> tftpd Start TFTP server Reading ::
Firmware upload and upgrade
Move to the directory where the firmware was previously extracted and upload it to the router using a TFTP client
tftp -m binary 192.168.1.1 -c put tomato-Netgear-3500Lv2-K26USB-1.28.RT-N5x--093-AIO.chk
The procedure is quite silent, so don’t touch anything and after some minutes the router will reboot successfully
Open your browser to http://192.168.1.1 and enjoy your new firmware.