If for some reason you brick your router and the failsafe mode of the OpenWRT firmware doesn’t work, you will need to debrick your router using a serial cable. Here is how you do it:
The v4.23 of the router uses the standard TP-Link pin-out, however the TX pin is not connected to the CPU. In order to make the TX line working, the two points on the bottom side of the PCB must be connected with a small wire. The pin at the SOC is labeled TP18, the one at the serial connector is labeled TP28. The RX line is 5V intolerant! So the connection needs a 3.3V RS232 level shifter. Pins on the connector of the board (look at the photos at the bottom of this post) are TX-RX-GND-3V3(VCC) (from left to right). After you solder all connections, you may use an USB to UART TTL convertor that you plug into your PC and use for example the cutecom application to connect to the /dev/ttyUSB0 device on your PC. Do not forget that you need to connect the TX pin of the convertor to the RX pin of the board and the RX pin of the convertor to the TX pin of the board. In case you use the USB to UART TTL convertor, you do not need to connect the VCC pin. Another important thing to do is to set the convertor to work with 3.3V if it can work both with 5V and 3.3V ! For more info look at the images at the bottom of this post.
After you are ready with your serial cable, you may proceed with the following steps:
Put the original openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-sysupgrade.bin (12.09-beta) or openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-sysupgrade.bin (12.09 Final) to your TFTP server.
Hook your router’s WAN Ethernet port up to your network/PC.
Hook up the serial cable/console as explained in the section “Serial cable for the TL-WR740N“, start your cutecom application, open the /dev/ttyUSB0 device, fire up your router and send a “tpl” command when your router shows “Autobooting in 1 seconds” to get console access.
Now we need to set router and server IP addresses (here named ROUTERIP and SERVERIP, substitute these with the real IP addresses). You’d better use these as IP’s: ROUTERIP->192.168.1.111 and SERVERIP->192.168.1.100. Type in the console (substitute as needed):
setenv ipaddr ROUTERIP
setenv serverip SERVERIP
printenv
Double check that the output of printenvlists the IP addresses you just set. Now we can load the firmware over TFTP with “tftpboot 0x80000000 openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin”:
ar7240> tftpboot 0x80000000 openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin
Using eth0 device
TFTP from server 192.168.1.100; our IP address is 192.168.1.111
Filename 'openwrt-ar71xx-generic-tl-wr740n-v4-squashfs-factory.bin'.
Load address: 0x80000000
Loading: #################################################################
#################################################################
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done
Bytes transferred = 3932160 (3c0000 hex)
Note the “3c0000” in the last line (your number may differ). Now execute the following commands, if necessary replacing 3c0000with the number you got from tftpboot:
erase 0x9f020000 +0x3c0000
cp.b 0x80000000 0x9f020000 0x3c0000
bootm 0x9f020000
You’re set, OpenWrt should now boot and you can set it up as usual.
dakle potpuno ista procedura kao za taj veliki fancy tplink je i za mali 700n tako da tesko da je tvoj 743 drugaciji
dakle kad ruter ispise: Autobooting in 1 seconds ti treba da posaljes "tpl"