IBM has tweaked their Model M design over the years, I thought it would be a good idea to make a thread to document this.
I noticed several differences while working on an M to F conversion kit. Check out the interest check (deskthority.net/viewtopic.php?f=7&t=24559 (http://deskthority.net/viewtopic.php?f=7&t=24559)) if you are interested - price would be $80 USD but we have yet to hit MOQs :(
I would love to see what Model M parts you have, please share in the comments and post pics if you can. Lexmarks/Unicomps etc are all welcome!
I will start. I have 3 variants:
IBM 1390120 02DEC86
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SDL controller sits on the back
(https://i.imgur.com/gYdy1RP.png)
Membrane is glued to the rainbow back plate
(https://i.imgur.com/lJpY3Th.jpg)
The spacebar stabilizer guides are glued to the top so there are no holes like in later models; it also has these on both of the 2u numpad keys
(https://i.imgur.com/a9bMXo7.png)
IBM 1395665 12-05-91
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Controller with non-removable cable screws into the back plate like this
(https://i.imgur.com/XbK4X9i.png)
but the bottom case still has the mounting tabs for the SDL controller!
(https://i.imgur.com/FlcYgR6.png)
Stabilizer guides for the spacebar are now built into the barrel plate - this presumably makes them harder to break but it creates holes in the barrel plate (due to the manufacturing process)!
(https://i.imgur.com/5nYyW3K.png)
Unicomp 1394204 May 17, 2000
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The mounting tabs for the SDL controller are gone
(https://i.imgur.com/cGAKiFG.png)
Channels for guiding spills through the board, but it seems a bit pointless when there are still holes for the spacebar
(https://i.imgur.com/2hvzLWL.png)