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.
It isn’t among the known part numbers for that system, though, and I have not yet verified what it expects to be connected to, interface-wise.
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
When you plug this in via PS/2, does it do what the keycaps state or something else? I’m asking since I’ve got an alphanumeric M50 (P/N 1395249) and despite having a QWERTY layout from the factory, it actually outputs what seems like a ‘corrupted’ form of AZERTY with random key placements down most of the middle column bank. I thus had to use a Soarer’s to do anything useful with it.
I have never attempted to connect this to anything, yet. I haven’t had a chance to trace out the pinout of the SDL connector and didn’t want to take a chance on it potentially being different from a normal Model M cable, and risk toasting the device. From how you describe its behaviour, it sounds to me like it’s approximately PS/2, and might help confirm my suspicions about what it’s used for (specially-equipped PS/2 systems).
This is one of many projects I have shelved at the moment, as I have other priorities I’m trying to get through. It will come up again in the future.