Check first that Tx and Rx did not get swapped from before modification to now.
Remember, with the jim.ftx board using an external reference, the external reference MUST be powered BEFORE the usb connection is powered.
Plug in battery, press power button to start the Kindle, plug in USB cable to PC.
That order, don't rush, you can follow plugging in the USB cable with another power button re-boot once the adapter has been powered on.
(I thought mine was dead for a long time until I stumbled onto that one.)
That shield is also ground - and actually easier to solder too than the board's internal copper ground plane (which is why it was so hard to solder the first time).
Very close to the shield and the serial port pin-out are a pair of resistors about the size of fly shit. A little stray heat and they come off.
I don't recall the PW-2 pictures posted here, but some Kindle models have those resistors INSIDE of the shield, where you can not see if they came loose.
Summer, Chicago - humidity should be too high for ESD to be a problem, but maybe.
But a stay "ground loop" between the soldering iron and the electronics could have killed the interface port(s) (either cable end).
(It doesn't look to me as if your using a hot air gun - which is even harder to use in this case - stray hot air is hard to control
.)
Beware of multi-meter in use. That is low voltage CMOS, the multi-meter must be an extremely high impedance type with a special "Diode" test range.
From the appearance of the work, you probably already know about that.
Could it be the adapter end?
Might have pulled or bent something on the other end of cable while working.
Duh....
All that comes to mind at the moment.