I was upgrading my WDR3600 with sysupgrade when my ssh connection closed. I waited a few minutes before restarting the router, but when I turned it back on all the LEDs flash and I don't see it sending anything on the network with tcpdump. I soldered headers to the serial port (following this debricking guide: http://dd-wrt.com/phpBB2/viewtopic.php?p=934517#934517) and connected it to my raspberry pi's serial port but I just get garbage (eg. "ëëïûÿOK{"). I'm using this command line for minicom: "minicom -b 115200 -o -D /dev/ttyAMA0", and only have ground, TX, and RX on the router connected to ground, RX, and TX on the raspberry pi (I also tried connecting TX->TX and RX->RX). I checked the pins with my multimeter and ground has 0v, power has 3.3v, RX has 0v, and TX has a constant ~2.3v. Also, my solder joints are pretty clean. What could the problem be?

Try 57600 baud rate.

The ground pin wasn't soldered well, I resoldered it and it's working at 115200 baud, but most of the characters are corrupted. I can make out some strings like "U-Boot" and "flash".

Edit: I got to the uboot command prompt and the RX on the router isn't corrupted at all so I should be able to set up the tftp server and flash it.

(Last edited by br1ckd on 25 Jan 2015, 23:09)

I realise this is an old posting but can't see an answer and I have a a very similar problem that might help.
My WDR3600 is effectively bricked. I've connected a USB UART to the serial port on board. All the internet sites say the port is a standard serial 8 bit, 1 stop bit, no parity, no h/w control. The weird thing is that with that config I receive scrambled text but can transmit commands un-corrupted. If I want to see what is going on and receive good data I have to set the com port to 7bit, 1 stop bit, no parity and no h/w control.
So for instance I can set a memory test going, reload putty in the 7bit mode and see the memory test perform perfectly.
I have no idea what is going on. I can't flash new data like this because I keep having to reload putty with the different config just to see the effect of the command.
Has anyone else seen this or know what is going on?