Replace the movement with an 'Arduino?'
I do find it somewhat Ironic that my interest in watchmaking lead me to work with surface mount microelectronics. What goes into these old electronics is fairly simple. The issue is that custom chips were used. Often mounted direct to the PC board. I went through a whole phase as I learned how the glass displays worked. A local surplus store had some stop watch displays. The tricky part is where the glass contacts the printed circuit. The best designs use a rubber contact strip. Some of the others use basically conductive ink silk screened onto tape. In theory the silicon should be fairly robust. I have chips that are nearly 50 years old. Most failures are likely to be in the support components. Audio gear is subjective to the capacitors drying out. I think watches tend to use ceramic caps.
One would probably need a logic analyzer to reverse engineer the electronics, although they are for the most part something called a 'binary divider.'
The bane of such devices is electrostatic discharge which was not well understood in the 1970s. Apple nearly failed with the Apple /// which was 100 percent DOA on first shipment due to static issues. So that probably precludes keeping a lot of these running.
I still have the stop watch projects somewhere on the back burner, which is so far back it no longer burns, and is quite cold. I guess a better analogy would be that such are buried somewhere out in the back 40.
-j
