RT-N66U bricked, possibly toasted. Possess USB-TTL adapter, need advise for next step

[wvy2610]

Hi all,

I have this RT-N66U for a while before it was hit by lightning and because I need router badly so I replaced it with RT-AC66U which is running on Merlin build and running fine at the moment. Recently I have a bit more free time so decided to give this bricked router a second look.

No matter when I try the ping command from my connected laptop to any lan port, there is no ping response from the router at all. When I try to go into recovery mode by pressing the reset button, the power led and the 5G led are solid. While the lan1, lan2 and Internet port led also lit up but the light is slightly dimmed as compared to the power/ 5G led (which is why I think the router is toasted). 2.4G led comes up for a while in between then goes off. If I hold the reset button long enough, the power led will start blinking until I release the button (I notice the led blinks when the bootloader reboots, you may refer bootloader.txt). Again, there is no ping response during the whole process.

When I try the WPS to clear the NVRAM, basically led sequence is the same as above except that the power led doesn't blink at all. So I decided to buy an USB-TTL adapter and try to read the bootloader sequence to see what is really going on inside. You may refer result in bootloader.txt attachment.

It will stuck at the dhcp lease fail infinitely after it rebooted itself 2 times (the result in the txt file attached only show last boot sequence after the 2 reboots due to the attachment size limit). Note that I have masked all the mac address if you are wondering. When I do a Ctrl+C during the first bootup, if I am quick enough I will be able to go into the CFE command prompt so I did a NVRAM SHOW and you may refer to the result in nvram_show_p1.txt and nvram_show_p2.txt (again, got to split the file due to the attachment size limit).

From the result I do see familiar IP addresses but like I said, there is no ping response at all, the lan port on my laptop doesn't even lit up. I would like to think that bootloader still working fine? If it is fine then there must be a window during the bootup where I can upload the firmware using my USB-TTL adapter? I have zero knowledge in linux or CFE so I might be wrong. Would really appreciate if someone can help to "decode" the bootloader and the configuration and advise what is the best next steps. What I hope is to bring back this router to working condition, doesn't matter if it is Asus stock, Merlin build (preferred and THANKS RMerlin!), DD-WRT or any other alternative, if it is still possible.

Lastly, I do apologies for my lengthy first post and I do enjoy this forum with all the great helpful people around.

Thank you.

 

[RMerlin]

Use Ctrl-C during early CFE boot to break into the CFE prompt.

You will also need to set your PC to 192.168.1.100 to be able to talk to the router - the N66U bootloader is hardcoded to use 192.168.1.1 instead of the value found in nvram (unless it was eventually fixed, but I doubt it).

 

[wvy2610]

Thanks RMerlin for your response. When I break into the CFE prompt, the led of lan1, lan2 and Internet is solid and there is no light on the Power. My PC has always been on 192.168.1.10 since I know the DHCP isn't working, anyway I tried all lan port and all I get is "PING: transmit failed. General failure".

Is there anywhere in the bootloader or nvram setting that says the firmware has a successful proper "hand-shake" with the hardware especially on the lan ports? That may perhaps explain why the the lan1, lan2 and Internet led lights are on while there is no cable and wan connection at all?

Thanks for your time on this.

 

[RMerlin]

Thanks RMerlin for your response. When I break into the CFE prompt, the led of lan1, lan2 and Internet is solid and there is no light on the Power. My PC has always been on 192.168.1.10 since I know the DHCP isn't working, anyway I tried all lan port and all I get is "PING: transmit failed. General failure".

Is there anywhere in the bootloader or nvram setting that says the firmware has a successful proper "hand-shake" with the hardware especially on the lan ports? That may perhaps explain why the the lan1, lan2 and Internet led lights are on while there is no cable and wan connection at all?

Thanks for your time on this.

I've seen a few reports of those specific three LEDs being lit, but none of those with that state ever had a TTL cable to see what was going on. All of them ended up getting their router replaced.

You could try wiping out nvram from the bootloader, with "nvram erase" then rebooting. See what happens then.

Otherwise, I suspect this specific LED pattern is a diagnostic code, but I have no idea what it means.

 

[wvy2610]

Fortunately I do have the cable and able to do the "nvram erase" and "nvram show", that is how I extract the bootloader.txt as attached in my first post.

Do let me know if you would like me to run a series of command in the CFE prompt to test the functionality of the lan ports, I would be very happy to do so. Here are the list of command that I can see which I am sure you already know:

CFE> help
Available commands:

et Broadcom Ethernet utility.
show clocks Show current values of the clocks.
nvram NVRAM utility.
reboot Reboot.
flash Update a flash memory device
batch Load a batch file into memory and execute it
go Verify and boot OS image.
boot Load an executable file into memory and execute it
load Load an executable file into memory without executing it
save Save a region of memory to a remote file via TFTP
ping Ping a remote IP host.
arp Display or modify the ARP Table
ifconfig Configure the Ethernet interface
help Obtain help for CFE commands

For more information about a command, enter 'help command-name'
*** command status = 0
CFE>

I do suspect the below message from bootloader (just before it goes into infinite "dhcp wan leasefail") indicates the lan ports are kaput:

et interface not found
No switch interface!!!:

I hope I am wrong, let me know what you think. Thanks!

 

[RMerlin]

I can't remember if it's necessary, but just in case, try to issue an "nvram erase" followed by an "nvram commit", and then reboot the router.

 

[wvy2610]

Thanks RMerlin, the erase and commit command doesn't seems to fix the lan ports problem. Guess I will just join the group to trash the device.

 

[Atais]

I know it is quite late, but.. have you tried the sequence like this:
> turn on
> asap push wps and hold ~10sec
> release, wait ~1sec
> push reset and hold ~5sec (better longer than shorter?)
- when you release the ping should work in ~ 5secs.

my router did not respond once too, and this helped.