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Alps SCK series



SCK is an Alps Electric classification code of uncertain scope. Thus far, it is associated with a series of “switchplate”–style mechanical switches based on Datanetics DC-50 series. As with DC-50, there is a sliding leaf spring that is assumed to provide the switch with hysteresis. There is thus a suggestion that the “switchplate” contact assembly itself could be inspired by DC-50, since Alps appear to be well aware of how it functioned. (It should be noted that Alps took over as Monroe’s calculator keypad supplier from Datanetics, so it would not be a surprise to find that Alps examined prior Monroe models.)

Two versions are known. One type has a custom shell with holes for four terminals, but is internally only has room for one contact assembly. The damping prongs associated with the “slits” on SKCL/SKCM switches are on the bottom of the shell and damp the downstroke instead of the upstroke.

The other version is single-pole only and shares the same shell as KCC series; this version is depicted in the photographs below. The “switchplate” is fitted without its actuator, as the sliding actuator replaces it. The raised area on the KCC shell can now be seen to serve a purpose, namely to hold the SCK external return spring. The shell is all black, instead of the usual two-tone black and grey of KBB/KCC/SKCC.

These switches are known from Roland’s CSQ-100 and CSQ-600. The CSQ-100 Service Notes are from 1979, and the CSQ-600 Service Notes are from 1980, putting these switches in the same general timeframe as KCC series. The “SCK” code is an older designation, and these switches would have been issued with a new designation in the early 1980s at the same that KCC series was assigned that name in place of the older SCH designation that appears to have applied to other mechanical types. As Roland also used switch KCA10037, it is possible that this became KCA series.


The following diagrams are based on SCH and SCK disassembly photographs from Deepak Kandepet, with initial measurements derived from SKCCBJ. The plunger is stamped metal, with a recess for the actuator spring. The actuator itself is almost identical to that of DC-50 series:

The actuator slides up and down in its recess by 1 mm. This deliberate backlash means that when the slider is released after actuation, the actuator does not move upwards until the backlash is cleared, giving hysteresis.

This explanation is not proven, but it is clear that this arrangement provides behaviour that differs from KCC series.



This switch is used in the Roland CSQ-100 and CSQ-600 (Roland part 001-276); the following photos were provided by System J Synthesizers and were taken while they had a unit open for servicing; the photos are public domain.

Contrary to tact switch numbering, this has a 1 in the subseries position despite not being LED-illuminated.

This switch was supplied by Alps with a 1-unit relegendable keycap, which appears to be encoded into the part number.

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This is Roland part 001-275. This appears to be the same switch as above, but supplied with a 2-unit relegendable keycap (based on the incomplete labelling in the CSQ service notes).

Four-terminal incapable

eBay listing 163839117115 includes a version of this switch with a lower shell that accepts four terminals. Inspection shows that internally it is still only capable of single pole operation as the shell only has room for a single contact module.