Editing SMK second generation

{{infobox dswitch
| image name        = SMK second generation.jpg
| manufacturer      = [[SMK]]
| switch type       = Clicky, tactile, linear
| contact mechanism = [[Contact mechanism#Metal leaf|Metal leaf]]
| keycap mount      = [[Keycap mount#Cherry MX mount|Cherry MX mount]], [[Keycap mount#Alps mount|Alps mount]], custom
| switch mount      = [[Switch mount#Plate mount|Plate mount]]
| family            = SMK second generation
| introduced        = 1986 or earlier
| product code      = 
| lifetime          = 
| force graph       = 
| peak force        = 
| patents           = [http://www.google.com/patents/US4866228 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 [[SMK Alps mount|Alps mount]] in the [[Apple Desktop Bus Keyboard]]), and J-M0404 series has been found as late as 1984.<ref name="Wouter" /> 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".<ref>AliExpress — [http://www.aliexpress.com/store/product/snip-overlong-URL/1140046_32656406285.html Buy 200pcs/bag Original Japan smk Keyboard switch with light KKM0611 0001 …]</ref> To date, this is the only known switch part number.

==Description==
The switches are all [[Switch mount#Plate mount|plate mount]], but they have been used in [[Switch mount#PCB mount|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 [[SMK vintage linear|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:

#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
#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:

<gallery widths="250" heights="187">
File:SMK second generation -- tactile and click sliders and leaves.jpg | Tactile (left) and click (right) sliders and leaves
File:SMK second generation -- click and tactile leaves, front.jpg      | Click and tactile leaves
File:SMK second generation -- tactile and click leaves, side.jpg       | Tactile and click leaves
File:SMK second generation -- tactile and click leaves, rear.jpg       | Tactile and click leaves
</gallery>

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

*[[SMK inverse cross mount]], SMK branded
*[[SMK Cherry MX mount]], SMK branded
*[[SMK Alps mount]], unbranded, and lacking the PCB fixing pins

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

<gallery widths="200">
File:Switch recognition--SMK--inverse cross.svg            | Inverse cross mount variant
File:Switch recognition--SMK--U mount.svg                  | [[keycap mount#Cherry MX mount|Cherry MX mount]] variant
File:Switch recognition--Monterey.svg                      | "Monterey" clicky [[keycap mount#Alps mount|Alps mount]] variant
File:Switch recognition--Monterey white.svg                | Tactile Alps mount variant
</gallery>

==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.<ref name="PCY-333U" />

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.

<gallery widths="200">
File:SMK Alps mount -- lower shell.jpg                     | 'T' pieces in the base which hold down the upper shell
File:SMK second generation -- retention clip release 0.jpg | Insert thin implement
File:SMK second generation -- retention clip release 1.jpg | Prise clip open
File:SMK second generation -- retention clip release 2.jpg | Upper shell fully clear
</gallery>

== Reassembly ==
Reassembly of SMK second generation switches is notoriously difficult. While there have been suggestions on how to accomplish this before<ref>https://imgur.com/a/foFNn</ref>, a refinement on this method follows. The order is quite important in achieving a smooth reassembly.

# Insert slider into top housing.
# Insert contact into the wider slot top housing, paying specific attention to the cutouts in the housing, and making sure the wire element of the contact is resting on top of the ramp. This should fit reasonably snugly once correctly in place.
# Insert the click/tactile leaf (if applicable) into the appropriately shaped slot.
# Hold the click/tactile leaf (if applicable) and contact in place and depress the slider.
# Insert the spring.
# Keeping the slider depressed, maneuver the bottom housing into place making sure to catch the spring into the nub on the bottom housing. Once you have the contact pins aligned with the holes on the housing, apply the necessary pressure to close the housing.

==References==
<references>
<ref name="Wouter">Wouter Scholten — [http://wouter.bbcmicro.net/bbc/serial_numbers.html BBC serial numbers and dates] Retrieved 2015-08-01.</ref>
<ref name="PCY-333U">MouseFan — [http://mousefan.telcontar.net/image/pcy333.htm SONY ? PCY-333 ? PS/2 Taiwan] (Japanese) Dated 2004-02-02. Retrieved 2015-08-01.</ref>
</references>

[[Category:SMK switches]]
[[Category:Metal contact switches]]
[[Category:Clicky switches]]
[[Category:Tactile switches]]
[[Category:List of all keyboard switches]]