SMK second generation

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SMK second generation
SMK second generation.jpg
Manufacturer SMK
Family SMK second generation
Introduced 1986 or earlier
Switch type Clicky, tactile
Sense method Metal leaf
Keycap mount Cherry MX mount, Alps mount, custom
Switch mount Plate mount
Patents US4866228 (1987)

SMK second generation is a provisional name for a family of low-profile keyboard switches from SMK introduced in the mid 1980s. SMK second generation switches are notable for employing three quite different switch mounts: Alps mount, Cherry MX mount, and SMK's own proprietary inverse cross mount (cross-shaped peg into a cross-shaped hole).

Identity

The official series name remains a mystery. The name "second generation" was selected to differentiate it from the SMK J-M0404 series switch. So-called "second generation" switches appear to have been introduced as early as 1986 (with the tactile Alps mount in the Apple Desktop Bus Keyboard), and J-M0404 series has been found as late as 1984.[1] No other SMK metal contact switches are known to exist, but the possibility remains that other metal contact switches could have been made before J-M0404 series or between J-M0404 series and "second generation" switches. US patent US4866228 A was filed in 1987, after these switches were introduced.

A pale blue slider, inverse cross mount switch with integrated LED has been sighted with SMK product name (「品名」) of "KKM0611-0001".[2] To date, this is the only known switch part number.

Description

The switches are all plate mount, but they have been used in PCB-mount keyboards as well.

As with their older switches, they are typically branded "SMK" on bottom. The only known exception is the Alps mount variant, which is unbranded; this has led to it being considered a clone.

Construction

SMK second generation switches function identically to their vintage predecessor: a leaf spring contact is held open by a ramp on the slider, which pushes it outwards and away from the static contact. Pressing on the slider lowers the ramp and allows the switch contacts to close. The second generation switch mechanism uses much smaller parts, reducing the static contact to a simple piece of bent wire. Switch reassembly is even more difficult than before.

The contact leaf's leg has a reinforced 'V' cross section, and the hole in the base is correspondingly a 'V', as with many Alps clone switches. The other leg hole in the base is circular.

Variants

Internals

SMK second generation switches are available in both clicky and tactile variants. These are differentiated by two changes in the internals:

  1. Clicky switches have a right-angled edge on the base of the slider where it engages the click leaf; tactile switches have this edge chamfered off
  2. The tactile leaf in tactile switches has more prominent engagement hooks — swapping in a click leaf still generates a click sound, as the more angled hooks are required in combination with the chamfered slider to keep the leaf spring from clicking

Tactile leaf springs are painted black, and the side wings have sweeping lead-ins; click leaves are bare steel with sharp angles.

The following photos are from Alps mount switches:

Mount

The internals were used together with three different keycap mounts, yielding the following sub-families:

Together with different slider shapes, the upper shells differ significantly between sub-families, while still following a common pattern:

Removal and disassembly

The upper shell features two retention clips which lock the switch to the mounting plate from below. To remove the switch from the keyboard, the switch must either be fully desoldered, or these clips must be pressed in while the solder is heated. Most switches will only be removable with the PCB fully removed from the keyboard, to allow access to the clips. The switch cannot be easily opened while still locked to the retention plate, although MouseFan appears to have achieved this somehow.[3]

There is a second set of Alps-style retention 'T' pieces which hold the upper shell down; these are covered over by the mounting plate retention clips, and can be released by prising them away using a long, thin implement. The switch cannot be opened while still locked to the retention plate.

References

  1. Wouter Scholten — BBC serial numbers and dates Retrieved 2015-08-01.
  2. AliExpress — Buy 200pcs/bag Original Japan smk Keyboard switch with light KKM0611 0001 …
  3. MouseFan — SONY ? PCY-333 ? PS/2 Taiwan (Japanese) Dated 2004-02-02. Retrieved 2015-08-01.