I bought this HP-97 on eBay a couple of weeks ago. I still haven't powered it up. I was thinking of removing the cable and putting it back in its original state but the connections inside give me pause.

I think the calculator may have been rigged to act as a controller. Why else would some of the keys be wired?

Here are some pics:

Blue and green wires going up are routed to this circuit board:

Edited: 2 Aug 2009, 1:58 p.m.

This 97 was made before HP offered the 97S, you can tell them from the layout of the main circuit board. The wiring looks to me like someone wanted to bring the same control lines out of this 97 as are brought out from the standard 97S. Most of the control lines are indeed accessible from the keyboard/display circuit board and that's why most of the wires go there. Furthermore, there seem to be 4 column scan lines going to the keyboard matrix and that's exactly what's needed for external keypad-like input.

So, this appears to be an early 97 that was retrofitted to interface to something like a 97S i/o pod.

Edited: 3 Aug 2009, 1:41 a.m.