TP-LINK WR740n bricked

After I attempted to flash the router with open-wrt I managed to brick the device after trying to copy the image it said not enough memory.

When it’s bricked all it does is flash all the lights.

If you connect to the serial interface that it spits out is this :

AP121 (ar9330) U-boot

DRAM:  32 MB
led turning on for 1s…
id read 0x100000ff
flash size 4194304, sector count = 64
Flash:  4 MB
Using default environment

In:    serial
Out:   serial
Err:   serial
Net:   ag7240_enet_initialize…
No valid address in Flash. Using fixed address
No valid address in Flash. Using fixed address
: cfg1 0x5 cfg2 0x7114
eth0: 00:03:7f:09:0b:ad
ag7240_phy_setup 
eth0 up
: cfg1 0xf cfg2 0x7214
eth1: 00:03:7f:09:0b:ad
athrs26_reg_init_lan
ATHRS26: resetting s26
ATHRS26: s26 reset done
ag7240_phy_setup 
eth1 up
eth0, eth1
auto update firmware: is_auto_upload_firmware = 0!
Autobooting in 1 seconds
## Booting image at 9f020000 …
   Uncompressing Kernel Image … Too big uncompressed streamLZMA ERROR 1 – must RESET

This is the official open-wrt page on the  TP-LINK WR740n :

http://wiki.openwrt.org/toh/tp-link/tl-wr740n

You have to solder a 3 pin connector (rx, tx, gnd) and then use a usb-serial convertor to gain access directly to the processor and a wire as in the picture between TP28 and the TP19 – the one in the middle.

Download putty, select serial select com port set Baudrate to : 115200 – and you should see something similar to the above code.

Type “tpl” in U-Boot to get a shell!

We need to set router and server IP addresses :

setenv ipaddr ROUTER_IP (eg. 192.1681.1)
setenv ipaddr 192.168.1.1
setenv serverip YOUR_PC_IP (eg. 192.168.1.2)
setenv serverip 192.168.1.2
 
printenv (to check the settings)
 
tftpboot 0x81000000 openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin 
erase 0x9f020000 +0x3c0000 
cp.b 0x81000000 0x9f020000 0x3c0000 
bootm 9f020000 

Additional info :

3932160 bytes openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin
3932160(dec)->3c0000(hex)
3932160 bytes = 3.75MB = 3c0000(hex) bytes

Additional resources :

• TFPD Server: tftpd
• OpenWRT Image : http://downloads.openwrt.org/attitude_adjustment/12.09-beta/ar71xx/generic/openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin 

To restore to original firmware :
 Download WinScp http://winscp.net/download/files/2014022215228bab04bc5bffbb6e9046e9d2395987b5/winscp551.zip

Transfer image to /tmp using the WinScp
http://www.tp-link.com/en/support/download/?model=TL-WR740N&version=V4#tbl_j

Connect with  putty on ip adress via ssh and type :

cd /tmp
mv wr741nv1_en_3_11_1_up(100312).bin orig.bin
dd if=orig.bin of=tplink.bin skip=257 bs=512
mtd -r write /tmp/tplink.bin firmware