Alps SCK series
SCK is an unconfirmed series of keyboard switch from Alps Electric. The shell is externally identical to that of KBB/KCC/SKCC series, but the slider is flat metal. There is seemingly no internal spring: the return spring sits on the outside. This is possibly a cost-reduced variant of KBB/KCC/SKCC without the complex contact assembly. It’s worth noting that the (truncated) circular raised area on the top of the shell serves a purpose in this design (to retain the external spring).
Curiously, 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 KBB/KCC/SKCC.
Typical Alps keyboard switches of this era had a code of the form Kxx10903. This switch has a totally different digit sequence to that of tact switches, which at present is impossible to decode, but in either case, implies that this was a huge series, which seems unlikely. There is also no explanation for why the series name begins “S” instead of the expected “K”.
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.
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).