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Cherry MY

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Overview

Cherry MY is the German Full-Travel Sealed Contact (FTSC) product range. Standalone keyboards with these switches have MY model numbers, leading to the switch technology also being referred to as “Cherry MY”, which allows it to be distinguished from the British and American FTSC products. In catalogues, the term “FTSC” is used. Most MY keyboard assemblies are placed into G81 series, but the oldest examples were given G80 model numbers, from when G80 simply denoted a German keyboard, in contrast with B80 full-size American keyboards (see keyboard codes).

Although “full-travel sealed contact” is a fairly generic description, it was not used for Cherry’s rubber sheet keyboard implementation, which was instead described as “NTK” (New Technology Keyboard), with keyboards being placed into RS (rubber sheet) series with G83 part numbers. Cherry’s The keyboard pros! catalogue from 2006/2007 confusingly describes FTSC as “mechanical individual keys with membrane contact switches”, presumably on the basis that every switch has a dedicated return spring and actuator spring within a discrete removable module.

History

The original design for a membrane keyboard with metal leaf actuators came from Cherry Electrical Products in the UK, with Allen Ellson named as the inventor. The patents were filed in 1984. Whether or not this design made it to full scale production is currently not known.

Demand from the German typewriter industry for lower-cost keyboards led Cherry Mikroschalter in Germany to investigate the UK’s existing FTSC system. Günter Murmann in Germany revised the design, adding the coil spring. This led to a second round of patents being filed in 1985 and 1986 for the redesign. Cherry MY is similar to the UK design, but was improved in order to yield a more reliable product. As Cherry in the UK already had a membrane production line built, Cherry in Germany made use of this facility for MY.

Peter Cherry, president of Cherry, took the decision to terminate the British FTSC system, as it made no sense to him to have two competing product lines. This left Germany making the keymodules and finished keyboards, and Britain making the membrane sheets. The membrane production line in Britain was also use for NTK (G83) until membrane production as a whole moved to Hungary when the UK operation was downsized. Some NTK membrane production may have also taken place in the US and Mexico, but details on this are distant and unclear.

The dates of introductions for the series are not known. Full-scale membrane production was already in place in May 1987 when engineer Keith Jones was hired by Cherry UK to improve the production line yields. Keith set up a new production line, which cut the failure rate of the membrane production by two-thirds from 30% to 10% (the limit of the budget available). He designed new tooling for cutting the membrane holes: the challenge with this was to prevent the burr from interfering with membrane spacing. (Keith noted that he subsequently designed a membrane production line with 250 ppm failure rate (0.025%) with a higher budget available to him, for Poly-Flex Circuits in the US.)

Patents

Patent Priority Filed Published Assignee Inventors
GB2141874B: Keyboard with membrane switch array 1984-03-29 1984-03-29 1987-04-01 Cherry Electrical Products Ltd
Cherry Electrical Products
Allan Ellson
EP0157035: Mechanical keyboard with membrane switch array 1984-03-29 1984-08-22 1993-01-27 Cherry Electrical Products Ltd Allan Ellson
DE3530050: Tastenmodul für Folientastaturen 1985-08-22 1985-08-22 1987-02-26 Cherry Mikroschalter GmbH Günter Murmann, Walter Mertel
EP0233926: Tastenmodul für Folientastaturen 1985-08-22 1986-07-31 1989-06-07 Cherry-Mikroschalter GmbH Günter Murmann, Walter Mertel
US4800245: Key module for key-actuated membrane switch panels 1985-08-22 1986-07-31 1989-01-24 Cherry-Mikroschalter GmbH Günter Murmann, Walter Mertel

Types

Cherry MY is divided into three types, of which one type has two variants. Current data is simply inadequate to get a clear picture of the distinction in date or usage between the three types. By the time that Acorn purchased from Cherry (which was before my cousin left in 1990 or 1991), Type 3 was already available, which can be see in the aforementioned data.

The type designations are not official, and simply serve as a way to refer to the different designs. Nothing is presently known about why the switch was redesigned twice.

Type 1a

Typically black plunger; UncleFan has found that—with the examples discovered to date—modules with upright keystems use black plungers, and those with angled keystems use clear plungers. Per the patent, the stationary tip of the leaf spring is visible in the retaining post. The upright and angled types can be seen together in the TA Gabriele 7007 typewriter; UncleFan has also found photos of a G80-0761 that matches the example posted to Cherry on Instagram (allegedly from 1989), which also appears to be from a Triumph-Adler typewriter.

Type 1 modules are heat-staked to the membrane backplate, meaning that the modules cannot be removed without damaging them, and they cannot be reattached after removal.

Type 1b

This is the typical form of Type 1, with the leaf spring retaining post fully enclosed, as seen also in the later types. These so far have only been seen with 0° keystem black plungers.

Type 2

This is a rare form with clear plungers of a different design. The modules are secured to the membrane backplate by feet that are spread apart by small pegs inserted to splay them out. This allows the modules to be removed and replaced without damage.

Type 3

The vast majority of FSTC keyboards use Type 3, with vaguely cylindrical plungers. As with Type 2, the plungers are clear instead of black, and the modules are safely removable from the assembly.

Parts

Part Type Source
MY1A-21NC Currently associated with the Type 3 actuator Cherry

Sources

See also