A now for something a little different. The glowy thing I mentioned earlier arrived. It was packed really nicely and even had its cover.
Tada, it's a TI 4000 calculator with, count 'em, 12 Panaplex digits. Woo!
The listing said it was working, but, alas, a few keys don't. However, it was cheap so I think I'll keep it. The display alone is probably worth it.
The keyboard is a sealed unit that, according to the
Old Calculator Museum, uses conductive pads to register key presses. So, that'll be interesting to investigate if the problem lies in the keyboard.
On the bottom side of the motherboard, it appears someone has been here before. There's flux in various places, including on one of the large DIP ICs as well as all the pins of the keyboard module. I guess this machine got lots of use.
The annoying thing is that several places have what appears to be blobs of clear epoxy (and less-than-stellar soldering). What's a safe way to get the epoxy off? It looks like the solder mask isn't all that durable.
Anyway, I think I'll save this one for when I have more time. It looks like it's going to take a fair bit of poking around and delicate surgery.