I don't have any of them around any more to check against. but it is either a 2-pin header next to the SATA signal connector, externally accessible(!), ..

.. or an unpopulated internal header on the opposite end of the circuit board. I suppose you could open one up and see if there are a pair of 0.10" spaced through-hole pads at the end opposite the SATA connectors. If so, then that's the "jumper" block. Otherwise it must be the one that is externally accessible.

EDIT: duh.. I see you've opened one up already.

Okay, so nothing at the far end. If that drive is of the generation that has the magic jumper, then it would be across the tx/rx pads at the connector end. Try jumpering those prior to power on and see if it comes up.