NEC oval

NEC oval
Manufacturer	NEC
Switch type	Clicky, linear
Sense method	Metal leaf

NEC oval (provisional name) is a series of mechanical keyboard switches developed by NEC. It has been found in a few NEC keyboard models, most commonly the APC-H412.

Variants

Variants of the oval series include:

	Colour	Type
	Blue	Clicky
	Heavy Blue	Clicky
	Cream	Linear
	White	Linear
	Heavy White	Linear
	Black	Linear
	Lock	Alternate Action

Blue

The blue switch is distinctive not only because of its oval shape, but because it is one of only a few types of mechanical switches that actuate before their click and tactile response occur (see force measurements, below).

In the APC-H412, the switch emits a characteristic ping upon bottoming out. In theory, the ping's frequency is at the resonant frequency of its spring, which may be somewhat loose in the key's resting position. Thus, bottoming out a key, or releasing it quickly, sends an impulse through the board that elicits the impulse response of a spring: vibration at its natural frequency. With multiple springs responding at different amplitudes, the whole board "sings".

Provisional force measurements are as follows:

45-50 g force, 2.5 mm travel - actuation
70-75 g force, 3.0 mm travel - click, tactile response
4.0 mm travel - bottoming out

Removing keycaps

The "normal" method of pulling a keycap can damage this switch. The switch's plastic top plate, which holds it together, is extremely thin. If you pull straight up, and the key is stuck in any way (easily true for a dirty switch), the force required to free the cap will break the top plate and everything will fall apart. Instead:

Grab both sides of the key with a Topre-style keycap puller.
With the puller vertical and perpendicular to the keyboard, rotate it to the right. The left edge of the keycap rises and the right edge either stays in place or drops.

Once the cap is removed, applying a lubricant such as Finish Line Extreme Fluoro between the keycap and slider makes it easier to pull them apart in the future.

Removing switches

The switch seems to be held in place by two solder joints, but removing these joints allows only the switch plate to come loose. The switch body is held in place by two extremely thin tabs. If you try to remove them, they break. (OP: I've already destroyed one switch this way; it will not mount again.) To remove the switch body, it's necessary to detach the mounting plate from the PCB, to which it's attached by several metal rivets.