I have been unable to confirm it as such, but I’m reasonably confident that this is the PS/2-compatible 4704 emulation keyboard used on various period IBM personal computers when acting as a 4704.
This is one of a handful of known keyboards (mainly if not exclusively, specialized function keypads smaller than a traditional keyboard) which uses the membrane buckling spring, but sandwiched in the style of assembly used for capacitive buckling springs instead. This enhances reliability/longevity, as failure of the plastic rivets can’t happen: there are none.
- Identification: IBM part number 1393915, manufactured in USA by IBM 1989-09-14
- Application: still figuring this out, suspect 4704 emulation on PC, PS/2 etc.
- Connectivity: SDL connector, unknown interface
- Key layout: 50-key matrix (grid) layout
- Keyswitches: tactile and ‘clicky’ buckling spring over membrane
- Acquired: February 2015, private sale online