Cool. So it's probably not my ribbon cable, then. The cable on my unit was badly pinched during factory assembly, and felt like it might be just hanging on by a thread. I did check it for continuity, though, and it seems okay, but I worried that might be just luck of positioning (bending).

But the symptoms you describe exactly match those seen here, so I'm inclined to assume the cable is working. One less variable to wonder about.

I'm wondering if maybe soldering that +5V (+4V?) pin might have leaked and shorted a trace on the underside or something. Nothing else in the hack is mechanically close enough to anything to worry about.

Let's see if David can send any hints (I emailed him) for what to measure. If not, I may have to break the seals on my other unit to compare signals/levels between the two.

Cheers