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SMK JM-0400



JM-0400 is a series of (for the time) low-profile mechanical and reed switches from SMK.

In SMK’s 1979 advertisement, the name “JM-0400” was given for the series. This reflects one of SMK’s nomenclatures. Boss on the other hand referred to J-M0404 subseries as “JM-0404” in parts lists. A Filcril advertisment in Elektor Eletrônica from September 1988 uses “Chaves para teclado - Séries JM 0404/JJ0019” instead, with “JM 0404” written without a hyphen and “JJ0019” without even a space. The J-Mnnnn and JM-nnnn formats seem to represent a presentational variation only. SMK themselves also used the format “J-M 0404”.

JM-0400 series contains both mechanical and reed switches, identical in size. The series is also said to contain “sealed membrane type units”, of which no further clarification is offered. The standard reed switches were assigned subseries J-J0019 which curiously falls entirely outside of the expected numbering range.



The only commonly-occurring JM-0400 switches are the mechanical family. The standard mechanical switches (momentary sloped) form JM-0404 subseries; other variations of the switches form additional subseries. These switches are well known from such keyboards as Apple’s M0110A. These switches have a very simple contact design comprising a horizontal stationary contact (shaped rather like a goalpost) and a flat vertical movable contact. The plunger holds the contacts apart until the key is pressed. The simplicity of the design led to it being widely cloned in the Far East. Some of these clones accept Cherry MX keycaps.


The reed switches are not known from any keyboard, but Deskthority topic SMK Magnetic Reed depicts a single reed switch that appears to be new old stock with no further details. The reed capsule is not only mounted diagonally corner-to-corner within the switch, but angled upwards too; most compact reed switches use one of those two approaches but not both.


The “sealed membrane type units” have never been seen.

Elastic contact

A single example of the elastic contact type is known, which is identical to the type used by Maxi-Switch. There is no evidence to confirm or deny that these are part of JM-0400 series; they are included here for now. This definitely appears to be new old stock. No indication is given of where either this switch or the reed switch came from, and although they are alleged to be SMK, the SMK branding is not depicted in either case.


Details on the switches are scarce. In addition to the brief advertisement in Computer Design magazine in 1979, the product range was also covered by an advertisement in JEE, Journal of Electronic Engineering somewhere between issues 193 and 198 (1983), as listed in Google Books. The complete advertisement cannot be viewed due to copyright and the incorrect uploading practice prevents the correct magazine from being located. “J-M 0404” is also covered in an advertisment that falls somewhere between issues 175 to 180 from 1981, again inaccessible. From these advertisements we are able to determine some of the specification and some of the subseries names.

Characteristic Mechanical Reed
Pretravel 1.5 mm
Total travel 3 mm
Contact rating 5 mA 12 V DC
Rated life 10 million cycles (later, 100 million) 20 million cycles
Bounce time 3 ms max
Contact resistance 1 Ω max


Part numbers take the form of the series name, then a hash (#) and finally a two-digit number. However, the hash portion is often omitted. The hash is sometimes mis-transcribed as “≠” or as “sharp”, or even “&”, “/” or simply “?”. Despite the number of places where the part numbers show up, all advertised stock anywhere in the world is fictitious: these switches are all sold out.

Subseries Description Part Part description
J-J0010 Unspecified reed
J-J0019 Momentary sloped reed J-J0019#10
J-M0404 Momentary sloped mechanical J-M0404#01
J-M0404#10 “PCB Dummy Keysw[itch]” (ISO Parts)
J-M0409 Alternate action sloped mechanical J-M0409#01
J-M0410 Illuminated sloped mechanical
J-M0432 Momentary stepped mechanical
J-M0434 Alternate action stepped mechanical

The part numbers all come from surplus sites. Part J-M0425#01 was discovered and could be related; it too has not been observed and carried no description. J-M0452#02 fits the same model number pattern, but it has since found to be a small TACT pushbutton.

J-J0010 is listed in a 1981 advertisement for J-M 0200 and J-M 0404 that also gives J-M0409 “Lock type” and J-J0010 “Reed switch type” under J-M0404, with no other details given.

Other brands


SMK made NEC-branded JM-0404 switches. These could be found in an NEC keyboard with an SMK-made PCB (indicating that SMK was involved in the manufacture) as well as in an NEC APC keyboard with an NEC-branded keyboard PCB and assembly.


Switches identical in design to JM-0404 but branded “Maxi” make up what appears to be Maxi-Switch 6000 series. These appear to be subcontracted out to SMK.

Clones of Mitsumi KAM

SMK produced clones of Type 1 “Mitsumi standard mechanical” switches, in momentary, illuminated, alternate action and double-action forms: these can be seen in a Swintec 8014 typewriter. These switches are based around JM-0400 mechanical switches.


See also