Already fixed, but it was an interesting problem so I wanted to share.
My controller wouldn't work after installation. I found a short between pins 8 and 10 on the controller connector. Desoldered the flex cable and found no short on either the flex cable or on the logic board. Soldered it back in and the same short was back!
I sure couldn't see it, even under a microscope, but it appears there was just enough solder mask missing on the pin 8 trace that the underside of the flex cable was shorting pins 8 and 10 once soldered in place. My guess is somewhere around the "1" in "10". I put down some kapton tape to cover the traces and then resoldered the flex cable in place. Works great now!
My controller wouldn't work after installation. I found a short between pins 8 and 10 on the controller connector. Desoldered the flex cable and found no short on either the flex cable or on the logic board. Soldered it back in and the same short was back!
I sure couldn't see it, even under a microscope, but it appears there was just enough solder mask missing on the pin 8 trace that the underside of the flex cable was shorting pins 8 and 10 once soldered in place. My guess is somewhere around the "1" in "10". I put down some kapton tape to cover the traces and then resoldered the flex cable in place. Works great now!