Jump to page content

Cherry M4/M5/M6 Series and Serie M7

Contents

In this section

On this page

Introduction

There are two separate keyboard switches series that have been mistakenly treated as one series, under various names. As more information has come to light (including drawings kindly supplied by Cherry US) the distinction between the two series can now be made.

The US-made switches are referred to as ‘gold “crosspoint” contact’, or M4/M5/M6 Series. M5 and M6 were also manufactured at Hirose in Japan. The German-made switches form Serie M7. Good evidence exists to indicate that we can distinguish the two types by easy visual indication, as noted under Design; in short, the US-made switches comprise Styles A, AB and B, and the German-made switches comprise Styles C (normal switches) and D (custom switches for Sagem). The US and Japanese-made switches have a gloss surface all-around, while the German-made switches have a matt textured finish to the top and often the entire switch.

Following the cessation of manufacturing at the US sites, Cherry US appears to have switched to buying in M7 switches from Germany, making M7 the final designation for these switches. This can be see in the Keyswitch M7 brochure from January 1994, printed in the US, but depicting German M7 switches.

The date on which US switch manufacturing ended is not known, but it seems to be at the end of the 1980s, based on when keyboard production moved to TG3 and German switches started appearing in US-made keyboards. Cherry placed an advertisement in Electronic Engineers Master Catalog 1988–89 in which the only keyboard products listed were German types (G80, MX, M8 and M7), suggesting that US switch production had ended by 1988.

M4/M5/M6 Series

At present, we assume that Cherry keyboard switch modules originated in Cherry US. In catalogues, these did not have a concise description, but were described as ‘Gold “Crosspoint” Contact Switch’, ‘Gold Crosspoint Contact Switch’ (without the quotation marks), ‘Cherry Low Profile Key Switches With Gold “Crosspoint” Contacts’ or simply ‘Cherry Key Modules’. This relates to ‘Cherry gold “crosspoint” contact switches for low energy circuits’, which spanned (in 1973) E21, E53, E63, E68, E78 and G13 enclosed switches (derived from Series E22, Series E51, Series E61, E69, E79 and Series E13 respectively) alongside S31 miniature open switches derived from Series S30 (referred to by keyboard enthusiasts as “mousetrap” switches).

The US-made switches originally had part numbers beginning 26x, with the following models listed in the 1971 brochure:

Model Type
261-0100 SPST-NO
262-0100 DPST-NO

Curiously, these types are not depicted with the mounting posts that hold a lamp PCB. Also, considering that the Cherry Precision Switches catalogue from 1965 already listed model numbers beginning with a letter, the use of numeric model numbers for keyboard switches seems uncharacteristic.

By 1973, the model numbering had changed to M5 and M6, with M4 added soon afterwards to cover the corner-illuminated types. See Schema for details. The standard models in advertised in Electronic Engineers Master 1973–74 were:

Model Type
M61-0100 SPST-NO momentary
M62-0100 DPST-NO momentary
M61-0800 SPST-NO alternate action

Additional types were advertised in the 1973 catalogue, as noted on the schema page. A 1985 Cherry advertisement in Electronic Engineers Master 1985-86 Volume B (scanned by Bitsavers) shows “M4/M5/M6 Series” and lists only part numbers for these three subseries. The existence of these designations three years on from the 1982 German catalogue (where Serie M7 is detailed) offers the final evidence that the two series (M4/M5/M6 and M7) were independent.

By 1979, the US catalogue also included one M71 type. The M71-0100 drawing originates from Germany, and this appears to be a German-made type imported into the US in order to offer a choice of corner illumination (US-made M4 Series) and centre illumination (German-made M71).

Origin

The Cherry C-73 catalogue (copyright 1972) notes that gold crosspoint contacts have “provided highly reliable keyboard switching for several years in thousands of the most sophisticated electronic desk top calculators and computer terminals”, suggesting 1969 or earlier (some point in time three or more years before 1972).

The Cherry KB79-2 catalogue claims that gold crosspoint switching “has provided highly reliable keyboard switching for nearly 10 years in tens of thousands of the most sophisticated, most demanding applications.” If this catalogue is from 1979 as the name suggests, that would suggest 1970, which is sufficiently similar.

However, Cherry’s Meet the PRO brochure (which appears to be from 1977) notes the following:

Best of all, the PRO is made by Cherry … the company with more than a decade of experience in the manufacture and application of commercial and OEM keyboards.

The company that first introduced gold crosspoint contacts to snap action switches for low energy solid state circuits. Then, applied this same innovative gold crosspoint technology to keyboards back in 1967.

It is not clear what occurred in 1967, as this would appear to be at odds with the previous information. However, the KB79-2 catalogue also notes that Cherry has “become a major source of keyboards since the original success of [their] low energy switching units in 1967. We can see that the low-energy gold crosspoint switches were absent in the Cherry Precision Switches catalogue C-663 from 1965, although S30 miniature open switches are included.

In addition, we also have several Cherry patents. US patent 3715545 covers the standard momentary design (single/double pole, and linear and tactile) and this was only filed in June 1971. If these switches really are from 1967, one has to wonder why it took four years to file a patent. The alternate action patent was filed in January 1972 (US patent 3770923) as though alternate action was introduced later.

Specifications

The following specifications were given for the gold “crosspoint” switches in 1971 brochures:

Operating force 2.5±0.5 oz
Pretravel 332±132″ (also given as 0.093±0.031″; approx. 2.4±0.8 mm)
Total travel 316″ maximum (approx. 0.188″, or 4.8 mm)
DC resistive load 3 W maximum
AC resistive load 3 VA maximum
Current (switching) 0.125 A maximum
Current (carry) 0.5 A maximum
Voltage 28 V maximum
Bounce time 2 ms maximum (typically 300 ms)
Initial contact resistance 200 mΩ maximum (typically 25 mΩ)
Rated lifetime 10 million cycles minimum

The 1973 and 1974 catalogues make no mention of rated lifetime. However, in Cherry’s keyboard switches advertisement in Electronic Design in October 1972, the switch contacts were reported to be “Tested beyond 50,000,000 operations.”

Illumination

Initially, Cherry did not produce illuminated switches. Instead, an illumination kit had to be fitted onto the top of a switch. Although not confirmed, this appears to be the purpose of the two posts on the older M5 and M6 switches. Such an arrangement can be seen on keyboard model B80-22AA, used in the ADDS Consul 880, Consul 880A and MRD-700 terminals. Here, it was used with alternate action switches that lack those posts.

Around 1974, both the US and German divisions of the company introduced illuminated switches: the corner-lit M4 series in the US, and the centre-lit M71 series in Germany.

Serie M7

Separately to the US-made switches, production of Serie M7 was set up in Germany. The origin of this series is not documented, but the M71-0100 drawing from Cherry-Mikroschalter dates to May 1974. The drawing for M73-0110 dates to September 1976. The latter clearly depicts a Style C switch, even though Style AB and B switches would see use in the US for years to come.

German production used part numbers following on directly from those in the US. Where the US-made switches had part numbers beginning M4, M5 and M6, the German switches used M7. However, while the US used separate series for the switches, all German switches fell under a single series. Variations in design were given subseries groups instead: M71 for simple illuminated, M73–74 for standard switches and M75–78 for complex switches.

M75–78 range from single-pole M75 to quad-pole M78. The catalogue indicates that these are side-illuminated, accepting up to two LEDs (one on the left, one on the right). The additional poles are obtained by splitting the stationary contact down the middle, and using side-by-side pairs of movable contacts (determined by opening up M76-0899 for examination). The general contact design remains the same, but adapted to fit up to four contact pairs in a single switch. The lamp conductors run down the outside of the switch. Alternate action remains possible, limited to double pole: two pairs of contacts on one side, and a latching assembly on the other. Not every such switch is illuminated: custom DPDT alternate action type M76-0899 is non-illuminated. It would stand to reason that single-pole non-illuminated would not exist (as it offers nothing over M73-0100) but four such switches can be found in G80-0075 (a standard 4×4 + 2×4 keypad), whose PCB is designed to provide illumination for those four keystations in the alternative model G80-0078. It would appear that customers choosing not to take advantage of the illumination—opting for G80-0075—would receive switches without lamp terminals. (Whether this is also true of related models G80-0156 through G80-0170 is not known, as those may not all share the same PCB.)

M7 plunger colours are poorly understood. The majority of examples have black plungers. The standard alternate action model M73-0800 has a grey plunger the same as the US equivalent model (M61-0800). M76-0899 also has a grey plunger, as does the custom German-made momentary type M51-0131 (a replacement for the US-made custom part), so grey could denote custom in addition to alternate action. White plungers also exist, but the exact reason is not yet clear (photos sent from Spharx to UncleFan suggest double pole switches).

A dearth in catalogues greatly limits our understanding of this series at present. It is however now clear that these switches are quite separate from their US-made counterparts.

Hirose M5 and M6

According to Hirose (per a reply from them on 2019-01-08), Cherry M5 switch was made in (or from) 1983 and M6 switch was made in (or from) 1985. In fact, 1985 is the year of manufacture of a Hirose-made B70-4753 with the elusive Style B′ switches, which may as of yet turn out to be the Hirose variant of M6.

So far it appears that Hirose-made M5 and M6 switches were largely identical to their US counterparts.

Documentation

Both documents were scanned and made available by Bitsavers under Cherry components.