Cherry M7 part number schema
The following page provides a reconstruction where possible of the Cherry M7 part number schema. See also the M4/M5/M6 Series schema.
This is the German series, originally manufactured alongside the US series with separate part numbers. The only useful known source of part numbers for Serie M7 is the Cherry Keyboards and Switches Catalogue 1982 (Germany), which covers a subset of the range. Four switches from the range are repeated in an undated, unidentified catalogue found by Brother Dragon (yab8433408) that—from the tiny fragment presented online—offers no insights.
The fine details of part number arrangement remain a mystery. There is still a permanently-zero position in all part numbers, and the stem design still appears not to have any formal representation in part numbers. Unfortunately the dearth of example part numbers, coupled with the sharp rise in options, makes this very hard to determine. In particular, there is only one tactile type, only one T mount type, and only one 10° type given in the 1982 catalogue.
Part number format
Part numbers follow this form:
The positions are as follows:
|2||7||7: Series number|
|3||S||Subseries (1, 3, 4, 5, 6, 7 and 8); for details see the subseries table below.|
|4||0||This is always zero in known types, just as with the US-made switches|
|5||T||Nominally this indicates the switch type; see the subtypes table below for details.|
The subseries are divided into three groups. Within each group, the subseries number indicates the number of contacts. The first subseries has one pair of contacts, and each related series after that has one extra pair. For example, M73 has one pair of contacts, while M74 has two pairs. M75 again has one pair, and thus M77 has two extra pairs (77 − 75 = 2), or three pairs in total.
The exact configurations are not known with complete certainty, because the relevant table in the 1982 catalogue is ill-conceived: it does not differentiate between inclusive (e.g. 2A+1B) and exclusive (e.g. 1A or 1B) contact arrangements, which is something you have to deduce and decode for yourself.
|M71||Centre-illuminated (possibly conceived as an extension of M4/M5/M6 series, and contemporary with M41)||1|
|M73, M74||Standard switches||1, 2|
|M75, M76, M77, M78||Complex design that supports up to two sprung-lead LEDs (for which there are dual-window keycaps) and up to four contact pairs||1, 2, 3, 4|
The subseries are given in more detail below. The contact arrangements are educated assumptions based on the parts list, because it is not possible to be wholly certain about what Cherry’s table represents. M71 can be ordered with or without a lamp; it is assumed that the LED for M75–78 is optional as it is likely that many customers ordered these only for the extra poles, rather than the illumination.
Note that “1A, 1B” (for example) below means that you can choose between 1A (SPST-NO) and 1B (SPST-NC) while “1A+1B” (for example) denotes both contact pairs being present in the switch (in this example, SPCO BBM).
|M71||1A (1 pair)||Momentary||Lamp||Straight, 0°||The internal construction likely disallows the alternate action assembly|
|M73||1A, 1B (1 pair)||Momentary, alternate||None||Straight, T; 0°, 10°||Standard single pole switches|
|M74||2A, 1A+1B BBM (2 pairs)||Momentary||None||Straight, 0° and 10°; T, 0° only||Second contact pair occupies the space used by the alternate action assembly|
|M75||1A, 1B (1 pair)||Momentary, alternate||LED (single or dual)||Straight, T; 0°, 10°|
|M76||2A, 2B, 1A+1B BBM and MBB (2 pairs)||Momentary, alternate||LED (single or dual)||Straight, T; 0°, 10°|
|M77||3A, 2A+1B, 1A+2B (3 pairs)||Momentary||LED (single or dual)||Straight, T; 0°, 10°|
|M78||4A, 3A+1B, 2A+2B BBM and MBB (4 pairs)||Momentary||LED (single or dual)||Straight, T; 0°, 10°|
Compared to the prior scheme, the subtype position has very few values.
|9||Only found in the part number of the one 2A+2B switch; previously it had been used for the one and only known 1A+1B switch.|