Linksys WRT610N v2.0
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 Generic Page
You may also want to read the Linksys_WRT610N page (not version specific).
NO "Easy recovery" after 30-30-30! please read this.
See details and other alternatives on recovery section.
NOTE: During configuration or flashing a device, the only cables that should be attached to the device are the network cable to your computer and the power cable.
Warning: This unit MUST use K2.6 firmware.
Make sure you use a firmware with wrt610nv2 in the filename for the initial installation like the one below:
First read the peacock announcement and note that this is a router that always needs a k26 build: http://www.dd-wrt.com/phpBB2/viewtopic.php?t=51486
Once you have read the required reading sections of the peacock announcement you are ready to flash:
a. Flash firmware through the Linksys WebGUI.
b. After a couple minutes you should see an "Update Completed Succesfully" Screen.
c. Wait...at least three minutes after that just to be safe.
d. Do a power cycle of the router. (Unplug the cord, count to 10 and plug it back in.)
e. Wait for the lights to return to normal, usually about 2 minutes.
f. Do a HARD reset. Wait. Check for the password page and login to change the password.
g. After you have DD-WRT on the router you can then flash a big build if you wish to, following the steps in note 1 of the peacock announcement: ftp://dd-wrt.com/others/eko/BrainSlayer-V24-preSP2/2010/12-24-10-r15962/broadcom_K26/dd-wrt.v24-15962_NEWD-2_K2.6_big.bin
Make sure that you do not flash any build to your router that has the name of a different model router at the end of the filename.
 Recovery (Unbricking)
[Doesn't work after 30-30-30 reset!] A simple way to recover a bricked device is:
- unplug all ethernet ports (Important!)
- unplug power
- plug power in
- wait 2-2.5 seconds
- press the reset button and keep it pressed for 5 seconds, then release it
- reconnect ethernet (DHCP shoud give IP address to computer)
- point your browser at 192.168.1.1. You should see a "Management Firmware update" screen where you can flash the original (Linksys) firmware.
Windows Vista/7 may have trouble with TFTP. Try using Linux or Windows XP. 
Alt Method by redhawk0
WRT610Nv2 debricking....Info and Howto
Just an FYI thread.....
I received a 610Nv2 today that was bricked. I tried the power cycle, reset button for 5 seconds, web browser management mode method for debricking....but I was without luck.
It would respond with TTL=100 all the time....even after a successful flash of the 610nv2 trailed build.
I believe the owner indicated that it was flashed accidentally with a V24 build. These 610Nv2 require K26_NEWD2 builds.
So...I installed my Serial header to see what was going on. It said the CRC was correct (expected and calculated were the same)....but the CFE saw it as an invalid header....even though it is the trailed build that had 610N in the header.
I tried to flash the OEM firmware...but tftp.exe won't accept a file over 4Mbyte....so....I used tftpd32 server to flash the unit using the serial port and CFE commands.
I renamed the Linksys OEM 610Nv2 FW to code.bin and pointed to its directory in the tftpd32 server program.
Broke into the CFE and issued the following commands to move the firmware to the unit.
flash -ctheader 192.168.1.10:code.bin flash0.os
(where 192.168.1.10 was the static IP assigned to my laptop running the tftp server)
when it finished programming....I typed "load"
The unit finished the process and rebooted into Linksys FW. Then I could load the K26_NEWD2_mini_610nv2.bin build through the Linksys FW upgrade tab.
power cycle, hard reset, then flashed the latest K26_NEWD2_14473_big.bin file.
power cycled, hard reset again...then configured. All working great on this unit....hard reset again...and shipping it back to the owner.
Hope it helps someone else...this was one of the trickiest Debrickings that I ever had to deal with. (first time with a 610Nv2 unit)
 NVRAM Erase breaks Management Mode
Many people have difficulties getting the 610nv2 into management mode using the technique above. It appears that after the nvram is erased (via a 30-30-30 reset for example) the regular "press reset after startup" technique no longer works. Alternatives are to recover via serial console, or to short two particular pins on the flash chip (see http://www.dd-wrt.com/phpBB2/viewtopic.php?p=387245#387245) during startup. Sadly tftp is not an viable option (it will appear to work if your firmware file is under 3.8MB, but the upload will not be flashed).