[Camouflage]

I know this has been covered before with similar Cisco routers, but there are a couple of gotchas with the WRT320N in particular that perhaps need explaining better ...

First, here's how I bricked it. The 'Peacock' thread is great at telling you not to put a 2.4 image on a router such as a WRT320N that requires a 2.6. However, the links to the builds and the enumeration of build numbers are confusing enough that I still managed to do it, and, as foretold, I did indeed brick it - power LED flashing, and LEDs of connected ports lit, but otherwise dead to the world.

During what follows, I pulled out the DC power lead and re-inserted it many times, and, as it started to get dark, I noted sparks, and not liking the look of that, I found a switched four-way, plugged the router into that, and used the switch instead. This also freed up a hand!

The 'Reset' button is wired incorrectly on these routers, so it's no good trying to do a 30-30-30 reset - nothing happens, either with 'Reset' or 'WPS'.

Nor did TFTP work in the advertised manner; despite numerous efforts, I never managed to get a ping response so that I could send an image.

GP106 is marked on the board, but I was sufficiently uncertain as to which exact point the label referred that I didn't fancy it.

So, already having a Sony DKU-5 serial cable, I used that. The main question was: how to attach it?

First I tried trimming down the connector on a four-wire ADSL RJ-45 cable and trying to hold it in the WAN Port by stuffing it with strips cut off old credit cards (which I habitually keep as they're very handy for applying filler paste when decorating, etc). However, although I managed to get communication, it was very unreliable - often corrupted, there was no prompt, and my keystrokes didn't register. Incidentally, when next I opened up the unit, I realised that the connector in the WAN Port and that in LAN Port 3 are simply hard-wired to each other.

A jeweller screwdriver of exactly the right size extracted those absurd screws, and a knife slid around the clam shells prised apart the plastic clips. Noting how the antenna are connected, I then disconnected them from the board.

Then I soldered the connectors directly onto the edge connector on the PCB:

1: NC
2: Tx (red on DKU-5)
3: Rx (blue on DKU-5)
4: NC
5: GND (orange on DKU-5)

I tried both Hyperterminal and Putty, but the former had the disadvantage that it tended to send the CPU to max if the router was physically disconnected - by power cycling - without disconnecting in Hyperterminal beforehand. This meant that one had to reconnect once the router started to boot, thus almost certainly missing the chance to interrupt it with <Ctrl-Break>.

Incidentally <Esc> works just as well as <Ctrl-Break>, and is easier and therefore quicker to do, while <Ctrl-C> suggested in the forums didn't work at all.

Powering up the router, and pressing <Esc> as it booted, this time everything worked as expected - there was no corruption, I got a prompt, my keystrokes were echoed, and my commands were obeyed.

Next I readied the tftp2 program with a WRT320N mini image.
dd-wrt.v24-18946_NEWD-2_K2.6_mini_wrt320n.bin

Back at the console, I issued the commands ...
nvram erase (not -erase as in some posts)
upgrade code.bin
... and, immediately after pressing return on the second command, clicked 'Upgrade' on tftp2. A short while later there was an encouraging success message, and the prompt returned again ...
nvram erase
reboot

And some while later I had a working router!

Thanks to all for the various pieces of information scattered about these forums that made this possible. Hopefully, having it all in this one place will help other WRT320N users in a similar position.