tp-link N600/tl-wdr3600 reboot looping

[aes]

I have been running version 1.5.9 and 1.5.8 successfully on my TP-Link N600 router for several weeks now but suddenly it started to reboot on its own with increasing frequency. Now it is doing it so often that I can't do anything with it.

Things I have tried:
- unplugging all network cables
- hard reset button
- log on quickly via web/wired interface and doing a factory reset (can't complete in time)

I see people mentioning connecting using a serial cable. Does this apply to this model of unit? I suspect something hardware wise has failed on it and I have to return it but since I changed the firmware worry that they will say the warranty is void.

Any ideas?

[ispyisail]

options

reset router to default

turn off wifi just for a test

[bardu]

Try another 12V/1.5A power supply.
I successfully debricked my unit (WDR3600) many times using 3.3V usb to ttl adapter.
You can easily open the router case and connect a 3.3V serial adapter w/o soldering (improvise with needles etc), use wdr4300 openwrt wiki.

[aes]

Well I managed to recover by pressing reset over and over at power up then doing generic telnet reset at this link

http://wiki.openwrt.org/doc/howto/generic.failsafe

It seems when I add port forwarding rules with upnp on it causes this reboot looping to happen. Managed to work around the need for port forwarding by putting the device in a dmz.

Thanks for the suggestions.

Al