I have a d-link DSL-3680, which I believe is a provider branded version of the DSL-2680 (Based on the identical specification, and similar release date).   I attempted to flash it with the unbranded firmware (and that's why...)
PCB photo

I've populated the serial header on the PCB.

JP1 pinout,  3.3V serial  115,200baud 8N1
  [x] : TX 
  [x] : GND 
  [x] : VCC 3.3V 
  [ ] 
  [x] : RX

If I boot the router then I get the following on the serial:

Bootbase Version: VTC_SPI_4M1.25 |  2012/6/8 16:30:00
RAM: Size = 16384 Kbytes
Found SPI Flash 4MiB MX25L3205D(06E) at 0xbfc00000

If I boot the router, while holding down the reset button, I get the following:

RT63365 at Mon Oct 31 08:19:49 UTC 2011 version 0.8

Memory size 16MB

DRAM Mode=00000000

Search PHY addr and found PHY addr=0

I can't get anything else from the router, it won't reply to keyed input either.     Can anyone suggest if it's recoverable, and if so what can I try next?