OK. Here it is.

The hub was originally a non-powered version, with no means to power it. However, there were pads marked '+5' and '-'. The +5 was connected to pads for a diode that was not installed in this un-powered model. The diode would have prevented the external +5 (in hubs that supported that) from going back towards the host. I wanted power to go back towards the host, so I simply jumpered the pads. A few quick continuity tests verified that the +5 line was connected through from the upstream (host) to downstream (devices) connectors. I soldered 2 wires to the pads marked '+5' and '-' .

I also de-soldered the host side cable, and soldered on the small end of a cable very similar to the one (and infact worked in place of) that shipped with the 770.

The battery box on the bottom was a device that held 4 "AA" batteries, and had a full size host USB socket on it. It was meant to charge devices that were USB Powered (such as a iPod shuffle), or a Mobilephone by using the appropriate cable. I verified that it did have circuitry to regulate the +5 volts. Output with fresh alkalines is ~4.9 volts. I de-soldered the USB connector, fed the 2 wires through a hole in the bottom of the hub, and through the place where the USB connector used to be. I soldered them to the holes for the +5 and - pins of the now gone USB socket.

The 2 units are held together by small screws that are long enough to penetrate up from the battery pack, and into the USB case, but not long enough to contact the bottom of the hub PC board. Due to the thickness and type of the plastic used on the hub, this is strong enough for me to pick it up by the hub and shake it (professional shaking of course - with batteries installed) without it comming apart. (I only ever use glue as a last resort.)

A few warnings: I don't mean to sound arrogant, but if you do not have the expirience in these sorts of things, and the proper tools, please do not try this.

Your granddad's Weller (you know - the one with the wooden handle, fabric covered power cord, and 1/2 inch wide chisel tip) is NOT the "proper tools" for this.

Be warned that slagging your 770 is a very real possibility.

Another hint: Look at the big (big is used realatively here) electrolytics as an extra step to verify the power paths, and to verify polarity.

In hindsight, it would be better to have the whole thing a little "lower profile" for travelling. I guess this could be done by using a different hub, or by putting the whole thing in a special project case.

I used this several times today, and the only real problem has been the previously mentioned keybounce issue.