I took it apart. I did not find board layout or teardown pics in master index, or google. :O
I see that this PW3 is well labelled on the PCB silkscreen. It has pads to install button switches, labelled "USB BOOT", "ON/OFF", and "RESET", and a set of pads labelled "SERIAL DEBUG" (which have had wires soldered to them in the past).
One of the testpoints is labelled "JTAG", but JTAG needs more than one pin, so some of those other testpoints scattered around the board must also be JTAG, or it may re-use pads for other functions...
Anyway, the "USB BOOT" switch looks a lot like the "magic key" we have been searching for, so we can probably update kubrick to support this device as well. Even easier now that amazon gives us full firmware images in the update files.
I will take photos and upload them to a new PW3 teardown thread, but I have outdoor chores to do first. The joys of home ownership, eh?
EDIT: I am thankful at this point that I have a very powerful magnet (harvested from a hard drive) mounted on a handle. The PW3 screw on the floor jumped several inches up to the magnet, allowing for fairly large sweeps to find it. This tool has not been used to swap hard drive head stacks in quite some time, so it is good to find a new use for it...