Jump to page content

Cherry gold crosspoint/Serie M7 design

Contents

Keycap mounts

In the 1973 and 1974 US catalogues, the only keycap mount offered was straight, also unofficially described as “bar” (a term now used differentiate it from straight when referrring to straight versus angled keystems). By 1979 (the next US catalogue discovered), T stem had become an option, although the majority of switch types remain straight mount. Discovered examples from the early-to-mid 1970s are extremely rare, so it is not clear when T stem became available. German switches supported T stem as early as 1976, as shown in the drawing for M73-0110, which is straight stem but it shows the Style C design with full support for T and cruciform stems.

After T stem became the de facto mount, space bar switches (in the US, at least) could still be found with a straight stem, such as in the Contact Systems CS-400CD (B70-4753).

Alternate action also remained straight stem in the US, simply because the design of the switch did not permit a T stem to be combined with the alternate action mechanism or a second pair of contacts. The German design did not suffer from this limitatation, but no German alternate action switch has yet been sighted.

In US convention, T-stem switches typically face right (⊢) with terminals 1 and 2 on the left, or in some cases forwards (⊥) with the terminals at the front. There does not seem to be any consensus for switch orientation with German-designed keyboards.

Slider colours

By and large, the sliders are all black. There are a few notable exceptions:

Styles

The standard momentary and alternate action switches from Cherry gold crosspoint (latterly M4/M5/M6 Series) and Serie M7 switches are broadly divided into approximately five different styles. This classification was created around 2016 before these switches were better understood, and the significance of these styles is still a matter of ongoing research; see the examples page for further information. Some styles have visually significant variation that may have chronological or other significance; these are classified as sub-styles.

Styles A, AB and B are the US-made switches, in apparent production order (AB was overlooked from the original classification and appears to fall between A and B, sharing characteristics of each). Switches from these styles fall within M5 and M6 Series. Style C is the German-made M73 and M74 switches. Style D is also likely to be German-made; their official designation is not known as they appear to be a custom type made for SAGEM. (A 1994 brochure suggests that regular M7 switches did not change design.)

The US-made switches are all smooth finish. The German-made switches appear to have started with smooth sides and a textured top, changing to all-over textured finish (seemingly the same as with M9), although this remains speculation due to the rarity of German M7 keyboards. Style D switches appear to all be textured finish.

The style classification only covers the standard momentary and alternate action switches. M4 (corner illuminated), M71 (centre illuminated) and M75–M78 (complex) are all distinct designs that can be recognised directly.

The styles are illustrated below. The differentiating characteristics of each style are highlighted in green for the purposes of recognition and identification. The drawings are broadly accurate to 0.1 mm, access to parts permitting; many thanks to UncleFan for additional photographs and parts that allowed the illustrations to be significantly more accurate and detailed. Note that there was quite a bit of production variation, and the drawings below will differ from some switches.

Style A

Style A is the oldest-known design, even if it is not the original design. This original design has two tall posts on the top. The purpose of these posts is unknown, but the catalogues suggest that they are for mounting an illumination kit. After M4 and M71 series were introduced, offering dedicated illuminable models, these mounting kits became redundant, as would the posts if this was their purpose. Even so, at least one circle is present on the top of almost all later switches, typically raised, but recessed in the case of Style B. Style D is the only style where they are completely removed. In Style AB, one of these vestigial posts is typically used for a mould identifier.

Style A′

In some cases, Style A switches have the side posts reduced to small nubs. These are classified as Style A′.

Style AB

Style AB falls in between A and B, with the offset wall around the slider aperture of B, but the squeeze-grip retention ramps of Style A. The posts are, as with A′, reduced to small stumps. The front post position (where the mould number is placed) can be either a recessed slot or a raised post (which raises more questions about the purpose of these circular positions).

Style B

Style B is notable for introducing distinct plate retention prongs. There is only one vestigial post position, offset from the centre, which appears to always be recessed. Style B is seen—albeit inaccurately drawn—in the Cherry M51-0131 design drawing.

The drawing for B is fudged, as the measurements are based on an RS-defaced B′ which is inexplicably 0.3 mm shorter than any other type. Without a real Style B switch to examine, it is impossible to know what Style B really looks like. It has proven impossible to make sense out of the measurements.

Style B′

Style B′ is largely the same as B. The most notable difference is that it has a pair of facing trapezoidal holes cut into the base; see under base below. The reason for these holes is not known. The only example examined to date has thinner stationary contact metal (see under contacts below) but at present it is not known whether this is a characteristic of age (as in, cost reduction over time) or whether this was a deliberate variation. The internal structure of the base has a protrusion where the stationary terminal passes through to grip the thinner metal, and this provides extra support by keeping plastic between the trapezoidal hole and the terminal hole; it is almost as though the thinner stationary contact was a result of the effect of adding the extra holes.

The base is also single pole only: the second set of internal support slots for the secondary contacts are not provisioned. However, Style B has also been found in this form.

The only confirmed instance of Style B′ in a finished product is in the external extension to a Hirose Cherry B70-4753 (as this section has no PCB and the bases of the switches can be seen). The B70-4753 itself also uses T-stem Style B or B′ switches, branded Cherry, and is dated to March 1985. While made in Japan, the extension area bears English legends.

These switches were also sold RS-branded with the Cherry branding crudely machined off. For some reason RS did not want anyone to know that these were Cherry switches. As they are not marked with the RS part numbers, it is not possible to ask RS for details on them.

It is also not clear whether any B′ switches ever used the mould cavity numbering scheme of B, as these switches are too scarce. The main body switches in the Hirose Cherry B70-4753 example appear to have B-style mould numbering, but are not confirmed as B or B′, while the RS-branded B′ switches do not use B-style mould numbering (and in fact lack any top cavity identity).

Style C

Style C is the German design, used by the parallel Serie M7, with separate part numbers to the US-made switches. The top of the shell is matte finish, and bears a number at each terminal position. Previously these were assumed to be the terminal numbers (1 and 2 for SPST and DPST, and 3 and 4 for DPST only) but in fact the lid is placed on randomly. Even the US 1994 M7 brochure depicts M7 with the two SPST terminals marked 3 and 4.

The slider core uses only a single design (instead of being different depending on whether straight or tee mount was chosen) and with narrower dimensions it permits tee mount switches to be double pole (not possible with Styles A to B).

Style C′

Style C sometimes features a lockout hole in the slider: this is a hole that passes all the way through the slider just above the top of the shell. Switches with this hole are denoted Style C′. This hole is used to lock out keys by passing a rod through it, which stops the slider from descending. At present, the chronological significance of this characteristic is not known. The only examples of the lockout rod being present is in a Style D SAGEM keyboard, but a G80-0130 keypad with C′ switches has been found.

Style D

Style D is rarely encountered, being found to date only in SAGEM keyboards (one of which is very similar to the keyboard from the SAGEM TX20 Telex machine). Its existence in a 1987 SAGEM/ИЗОТ keyboard suggests that this is an alternative version to C, and not a replacement to C. It has prominent plate retention clips that appear to be able to be engaged from above the plate, and graphical Cherry branding. This is the only style which completely lacks circles on the top.

The stationary contact design is roughly the same as Style C but it has two tabs that engage with the shell, instead of one; see below.

More notably, the keystem is Clare-Pendar mount, which may have been at SAGEM’s request to permit existing French keycaps to be used. There is a tentative suggestion that older SAGEM equipment used Clare reed switches.

Style D switches all feature the lockout hole in the slider seen in Style C′.

Contacts

Stationary contacts

American and German switches use different stationary contact designs. The patents, from 1971 and 1972, show the stationary contact to be a rectangular sheet of metal. However, likely to save costs, the US and German factories each removed some of the metal. The US design removes metal from the sides, with a characteristic triangular section at the top. The German factory removed metal from the centre.

Style D stationary contacts have a slightly different top, with two raised blocks instead of one.

Style A M61-0100 has metal around 0.8 mm thick. The Style B′ switches supplied by RS use noticeably thinner metal, as noted earlier, at around 0.5 mm thick. UncleFan’s Style AB and Tom Hunter’s Style B both appear to be the thicker metal, suggesting that the thinner metal is specific to Style B′. German-made switches use stationary contacts around 0.77 mm thick.

Movable contacts

The movable contacts are all very thin, typically in the region of 0.1±0.02 mm, although Ed Ferraton’s M73-0120 use thicker metal, closer to 0.15 mm. Ed’s also have a groove stamped into them in such a way that the terminal remains flat, while being less flexible than if the groove were not present.

Base

Even the design of the base varies between US and German production. The base is 2.6 mm tall in US styles and 2.4 mm tall in German styles. In both cases, the base is permanently attached (perhaps with glue) and has to be either pulled off, or in most cases sliced off with a knife.

German-made switches have standoffs over the unused terminal positions in single-pole switches. They also have a small inset area at the bottom.

As noted above, some US-made switches have trapezoidal holes in the base; these are a variant of Style B, denoted Style B′.