Mitsumi standard type 2 (anomalous)

AliExpress seller Harry Ke found two types of Mitsumi standard mechanical type 2 switch: tactile (Mitsumi part E25-33-137), and tactile with LED. I was able to purchase a small quantity of the former, but only received one of the latter due to an MOQ of 1000!

Assorted non-LED switches

Type 2 switches

Non-LED version

LED version

LED switch with keycaps from an Apple Keyboard II (Mitsumi hybrid switch, tactile)

Both switch types are the comparatively unusual Mitsumi mount; the non-LED switch is effectively the same as the one used in the Commodore Amiga 1000 keyboard. However, on closer inspection of both the non-LED and LED switches, they are anomalous: the switchplate actuator leaf is not the normal shape found in type 1 and type 2 switches. The remainder of the switchplate appears to be identical. It is also interesting to note that the hole in the lid for the slider is not the same shape in both switches.

As with all the Mitsumi standard mechanical switches, they are branded on the bottom. Mine read “ミツミ” (Mitsumi); later switches use “M”.

Regular switch, base

LED switch, base

Disassembly involves sliding a long, flat implement behind the plate retention clips on either side of the switch. The retention clips are on the outside of plastic strips, and the sides of these strips engage with small tabs that secure the lid. Each strip has to be carefully pried away to release the lid; this is not easy, but nor is it particularly difficult. Once the lid is released, the switch slides apart:

Switch partially opened

Cover removed; the retaining tabs on the base can be seen, two on either side

Slider removed

Both the LED and non-LED versions are the tactile variant. Just as with Mitsumi miniature mechanical, the tactility is achieved by a horizontal coil spring slung inside the slider. As the slider is depressed, the spring wraps around a post in the base of the switch. The two switch series feel fairly similar; the miniature switches have a softer feel, while the full-size switches are rather more scratchy, quite audibly so.

The slider design used in these examples is non-reversible, but the shell is designed to support DPST operation, with two pairs of holes for the legs. Two switches can be placed back to back, with their legs inserted into the unused holes for the second pair of terminals:

The aforementioned switchplate is of an interesting construction. It comprises two flat metal plates that lie in the same plane. One of these has a tab that folds back against itself, which holds a two-pronged narrow copper leaf with a gold-plated tip. These metal plates feature a number of small tabs; these tabs are placed through holes in a flat plastic plate, and bent over to secure the assembly. A flap in this plastic plate presses the copper actuator leaf against what appears to be a small gold-plated prism formed from the other metal plate. These metal plates also function as the switch’s terminals.

This might be the first time that a Mitsumi switchplate has ever been disassembled. I didn’t try to remove the copper leaf, as there is very little chance of removing it without very visible damage, or of reassembling the switch afterwards.

Disassembled apart from the switchplate

Rear of the switchplate

Disassembled, top views

Disassembled, bottom top views

Echoes of the switchplate design are present in the contact assembly of the miniature mechanical switch:

The LED switch design is similar. Curiously, the LED itself is recessed some way down inside the shell, instead of being level with the top of the shell or protruding from it.

Revisions

2015-07-26: original document
2017-05-31: additional image to show the start of the disassembly process, plus slightly expanded disassembly description