Mitsumi standard mechanical
“Standard mechanical” is the provisional name for Mitsumi’s standard size discrete metal contact switch modules. This name is in contrast with the “miniature mechanical” switches that are distinctly reduced in size.
The PCB codes on some Mitsumi keyboards provide the series names of the keyboards and switches. Only two such names have been recovered for standard mechanical:
In theory there should also be KCM linear switches. No type 1 tactile keyboards are known.
Standard mechanical switches came in two sizes: the older type 1 switches with tall sliders, and the presumably DIN-compliant type 2 switches that share the same slot-mount plunger principle as used with Alps KFL Series and SKCL/SKCM Series.
Further detail on some of these switches can be found on the following pages:
Standard mechanical switches use discrete contact modules that can be inserted and removed as a self-contained unit. Just as with the Alps design change from SKCC to SKCL, the contact module design in type 1 and type 2 switches is completely identical and the modules are fully interchangeable between switches:
Depicted above are, from left to right: type 1 linear, type 1 latching, and type 2 latching.
The contact module colour appears to have changed over time. type 1 contact modules are a medium blue colour. Type 2 modules came in two colours: a deep turquoise/cyan colour (a slightly greenish blue) very similar to the original blue, and unpigmented plastic (“clear” or “colourless”). The two type 2 colours can be seen in the photos below, depicting ostensibly switches from the same packet of Apple service parts:
rzw’s Apple Extended Keyboard II shows the opposite to what I have: a colourless contact module for the tactile switches, and a turquoise module for the latching switch.
The exact sequence of contact module colour change is not yet known for certain, but it would seem reasonable to assume that the turquoise modules came before the colourless variety. The latching switches used in the Apple Extended Keyboard II demonstrated another variety: the upper shell of the switch could be either deep blue (as in my collection, shown above) or colourless (as in rzw’s AEKII photos). Because the type 1 latching switches were coloured differently to the linear switches, there is a suggestion that the wholly colourless variety came later, and that Mitsumi were cutting costs through avoiding unnecessary pigmentation (the linear switches are already a different shape).
The above still does not account for the anomalous type 2 switches with colourless contact modules.
Some type 2 examples use a different shell design. These are rare, but all indications are that they are genuine Mitsumi. The difference is subtle: normally the top of each plate retention clip has a “[”-shaped piece when viewed from the top, but this portion is solid on the alternative design. (The difference is not easy to explain.) The alternative design can been seen in at least two keyboards:
- Monterey K7S (Mitsumi mount, with separate switches for space and caps lock) ca. 1986
- Commodore 900 prototype keyboard (Mitsumi mount), ca. 1985
The Commore 900 keyboard also features the only known instance of a miniature version of the switch designed for thin function keys. This design parallels that found on some keyboards with Alps KFL and SKCL/SKCM switches.
The Olympia Startype electronic typewriter uses a variation of type 1 standard that has been adapted to accept the keycaps used with Marquardt switches.
SMK produced clones of the “Type 1” switches in momentary, illuminated, alternate action and double-action forms, as seen in a Swintec 8014 typewriter. The visible ICs in the machine are all from 1985, giving an idea of the age of the switches in this example. These clones are a modification of SMK JM-0400 series.