I used the re-flashed retail unit with no hardware modification for an hour or so. The mini-USB supplied power. The Avalon USB plugged into the side. I removed one of the screws from the top of the Avalon and fed the USB cable through the slot, and mounted the TP-Link outside the case.
I later modified this unit, I removed a 0R resistor to disconnect the internal antenna, and added a 0R resistor to backfeed power from the Avalon USB connector, and added the antenna, and replaced the dead internal unit, and closed it all up.
Does the blue light stay on with your TP-Link? If you push the reset button while it is starting up, does the blue LED flash about twice/second?
Are you trying to connect via the LAN jack? I think the WiFi has to be configured.
Can't the original TP-link be send to TP-link for reflashing? Maybe for a small fee or so?
There is a serial connection on the board of the TP-Link to do a serial boot. The OpenWRT community is very familiar with this process. The gotcha with the TP-Link is that those traces are very fragile, and if someone tacks wires to it and does not provide strain relief, they will rip the traces off the board.
I might be willing to sell a spare 703n flashed with the ckolvias latest release firmware, and to buy a distressed unit. Shipping would cost almost as much as a buying a new unit, then there is my time, so I am an expensive, last resort option.