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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. Some if not all of the mechanical types are contained within subseries JM-0404 (this is for example how Boss referred to the series in parts lists), which is also referred to as J-M0404 in SMK’s J-M9031 keyboard brochure. The J-Mnnnn and JM-nnnn formats seem to represent a presentational variation only.

JM-0400 series contains both mechanical and reed switches, identical in size. The mechanical switches were rated at 10 million cycles, and the reed switches at 20 million cycles; mechanical subseries J-M0404 was later rated for 100 million cycles. Both series were rated for 12 V DC at 100 mA, with 1 Ω maximum contact resistance. Bounce time was 3 ms maximum.

The series is also said to contain “sealed membrane type units”, of which no further clarification is offered.

A Filcril advertisment in Elektor Eletrônica from September 1988 mentions:

Chaves para teclado -
Séries JM 0404/JJ0019

“Chaves para teclado” means “keyboard switch”. The meaning of “JJ0019” is not known, but part J-J0019#10 exists. Here, “JM 0404” is written without a hyphen at all.



The only commonly-occurring JM-0400 switches are the mechanical family. At least some of these are in JM-0404 (J-M0404) series. 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 a single example is known, that may be new old stock. The reed capsule appears to be 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.


JM-0404 (J-M0404) contains mechanical switches. Various part numbers have been recovered but not a single one has been mapped to a known switch.

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.

Part no. Description Source
J-M0404#01 SWITCH Abtronics
J-M0404#04 Switches Jotrin
J-M0404#05 PCB Single Keys[witch] ISO Parts
J-M0404#10 PCB Dummy Keysw[itch] ISO Parts
J-M0409#01 REF.042R Abtronics

Other models that could be related are J-M0425#01 and J-M0452#02, also not observed.

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 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