The TX81Z developed some problems: it was forgetting edits to presets and decided to transpose up or down whenever it wanted, and preset titles got progressively more glitchy.
Apparently the TX81Z has an internal battery like a Game Boy game. It's soldered on. You gotta take it out and put a new one in.
- You want to open both the top and bottom, and desolder from the bottom.
- The battery comes on legs; desolder the legs from the bottom of the board and pull it out of the top, don't try to desolder the battery itself.
- I got some cheap cr2032 holders; these aren't the through-hole kind (I don't think the ones I could find would fit on the board). This worked great; I pushed the wires through from the top and soldered them in the same points as the original holder. One complication that I didn't realize was that these each hold two batteries; I just soldered some wire in.
- Just tape the holder to the board with electrical tape, there's plenty of space.