Alps elastic contact types
Elastic contact switches (previously known as “integrated dome” switches) use conductive rubber domes as part of the contact mechanism. The term “integrated dome” arose from these switches being discrete units that each contained a single rubber dome.
Elastic contact switches originally (or at least previously) used series names beginning “KE”, which was later amended to “SKE” (see series names). It appears that Alps eventually ran out of SKE* series names, and extended the range into SKP*. The only known keyboard type in this latter group is SKPA. In Alps literature, SKE* and SKP* are listed together as one collective group, which falls within the tact switch classification. In a 1983 advertisement in Computer Design magazine (see Documentation, below), Alps TACT switches were divided into two types: the conductive rubber types were classified as “series KE”, and the mechanical contact types were “series KH”.
There is no conclusive list of elastic contact types; the list below shows all types discovered to date. Photos of the keyboard switch types are mine; all other photos are misappropriated stock illustrations. Some types are confirmed to exist, but have no available photos.
Older types are assumed to have three-letter series names unless confirmed as being included in the renaming exercise. Newer series (SKPA onwards) are assumed to have four-letter series names.
||Yes||Non-keyboard pushbutton||This is an elastic contact type, misreported as metal contact in the 2000/2001 European catalogue; KEC10901 was used in the Yamaha SU700 alongside Hirose Cherry MX1A-0NNN|
|KED||Yes||Keyboard switch||Used in the Roland TR-808 (KED10903 and KED10001); the former was also used in the Boss DR-55|
|Yes||6.0mm Square Type (Snap-in)|
|KEH||Yes||Keyboard switch||Used in some TRS-80 machines, as well as the Roland MC-4 (KEH4A006) and JUNO-6 and JUNO-60 (KEH10003)|
|KEJ||Yes||Non-keyboard pushbutton²||Type KEJ10901 was used in the Roland JUNO-60|
|SKEL||Yes||Unknown||Part SKELAJA010 exists; SKELAK was used in the Roland MKS-20|
|SKEQ||Yes||SKEQFA was used in the Roland MC-500 Mk II|
|SKER||Yes||Reported to have been found in a Panasonic typewriter in keyboard model KFERAA001A; cruciform keystem, seemingly plate mount|
|(S)KEU||Yes||DIN-compliant PCB mount keyboard switch||SKEUAA is the model with a white plunger and inner post in the mount slot; whether the cyan type missing the inner post is also KEU/SKEU is not confirmed|
|(S)KEV||Yes||Exposed dome switch||Part SKEVAA is used as the reset switch in the Sega Genesis II|
|(S)KEW||Yes||Keyboard switch (Alps keycap mount, plate mount, two-piece shell)|
|SKEY||Yes||Exposed dome switch||SKEYAG was used in the Yamaha RM1x|
|SKPA||Yes||Keyboard switch (Alps keycap mount, plate mount, one-piece shell)||White is SKPAAA, and black may be SKPAAB (no details found with that part number)|
|SKPD||Yes||7.8mm Square Type (Radial) SKPD Series|
|SKPE||Yes||6.6×6.3mm Low-profile and Heavy Operation Type TACT Switch||Seemingly discontinued|
|SKPF||Yes||Long-travel Type with High Operation Force (Snap-in)|
|SKPG||Yes||High Operation Force Type with 5.0mm Height (Surface Mount)|
|SKPH||Yes||Listed in the 1993 Alps catalogue|
|SKPL||Yes||6.45mm Diameter Low Contact Resistance Type with Round Terminal (Radial)|
|SKPM||Yes||Low Contact Resistance Type (Surface Mount)|
|SKPR||Yes||High Operation Force, Low Contact Resistance Type (Surface Mount)|
|SKPS||Yes||Contact Resistance Type (Surface Mount Type)|
The identity of semi-integrated dome has yet to be determined. Several switches are similar, but not close enough.
SKPD has two terminals instead of four, which seems to rule it out.
SKEY series is a candidate, but no SKEY types have been sighted with the correct dome shape.
Like SKEY, SKEVAA is close, but both types have legs that protrude slightly from the sides of the switch. The switches in the ICL One Per Desk seem to have recessed legs that are covered over by switch. SKEVAA has the recess in the centre of the dome, but it is a much deeper recess than that of the switches in the ICL computer.
There are at least two reported failure modes of Alps elastic contact switches. The rubber domes can split, and the conductive coating can fail.
Conductive coating can be remedied with the application of electrically conductive paint. Alternatively, another conductive material can be applied to the dome.
Where the domes have split, replacement domes will need to be sought. Replacement domes can be obtained from the same switch series, or another series with the same type of dome. When seeking out switches, there are two considerations: dome dimensions, and operating force. Replacement switches may come with domes that are significantly lighter or significantly stiffer than the failed domes.
The various keyboard types appear for the most part to use identical domes. KEU/SKEU, KEW/SKEW and SKPA all use indentically-shaped light grey domes that are 5 mm tall and around 10.3 mm in diameter. KEH also contains a coil spring to provide pretravel, and the dome is a different design to suit the needs of that series.
KEC/SKEC and KEJ also use the same size dome, much smaller at 5 mm diameter and 3 mm in height. Belganet Dataelektronik stock unidentified Alps switches (listed as 589A0000) that have been found to be KEC/SKEC series; the domes in these are stiff, and possibly they are the 200 gf KEC10903 type. These domes can be used to substitute other KEC and KEJ types.
- See Alps Tact Switches sample card of unknown date.