Pin spring for latching (CapsLock) Keytronic Foam & Foil

[pl212]

I'm trying to figure out the dimensions, or perhaps get a picture, of a very small spring that I think is inside latching Keytronic Foam and Foil switches. At the least, such a switch is present on the Apple Lisa (wiki/Apple_A6MB101) for Caps Lock.

This spring - or some other pressure mechanism - presses against a tiny brass pin in the moving part of the switch, holding it tight against a white plastic race that contains the two pathways for the latching mechanism. Without this spring, the brass pin recedes totally into the switch. My estimate based on the size of the plastic hole, and the depth to which the pin recedes without the spring, is that it would have both an Outer Diameter and Free Length of 1mm. Tiny!

The brass pin, a little bit extended from what I assume is its normal position:

IMG_3571.jpeg (54.98 KiB) Viewed 9192 times

Pin pushed in -- nothing to stop it from receding totally into the switch:

IMG_3572.jpeg (61.87 KiB) Viewed 9192 times

Closeup of the plastic race which guides the pin into lock and unlock states. Note how there seems to be some conturing of the pathway, so that a pin pushed forward by a spring would click past a certain point and have to move in a different direction:

IMG_3573.jpeg (94.41 KiB) Viewed 9192 times

The switch reassembled, including the white plastic frame that holds the latch mechanism together:

IMG_3576.jpeg (67.02 KiB) Viewed 9192 times

Here's a thread elsewhere with the same question: https://www.eevblog.com/forum/vintage-c ... ce-131423/. Because this mechanism is prone to semi-explosive propulsion when the support bracket surrounding this switch is removed, my guess is that both myself and the person linked above have lost this very tiny spring -- or perhaps this happened with a previous owner's disassembly. Thanks for any thoughts or knowledge of how such pins are held in place in other switches!

[Muirium]

A spring that small just might have disintegrated over all these years. Surely it’s kept locked inside securely, or they’d have been a manufacturing (and service contract) nightmare! The Lisa was a $10k business machine after all, leaving Apple on the hook for mistakes like this.

[vtgearhead]

For folks who have had that little spring fly off into oblivion, I feel your pain. Despite being very careful I recently had the caps lock on a Corvus Concept keyboard spontaneously disassemble on the bench top. By a sheer miracle I found all the pieces and was laboriously able to reassemble the basted thing. I'm not sure where you'd find a replacement spring that small. It's a bronze coil spring with an outside diameter a bit smaller than the pin. Almost watch-mechanism small.

[wowijodo]

Totally feel you — those tiny springs are like ninja escape artists.

Mad respect for managing to reassemble it!

[wowijodo]

Trying to track down exact specs for old hardware parts like that tiny spring can definitely be a rabbit hole — I’ve had similar hunts when restoring vintage tech. At the same time, handling other tasks like customer support was getting overwhelming, so we decided to go with a call center outsource solution, which honestly took a huge weight off our shoulders. It gave us the breathing room to stay focused on the technical deep dives without getting swamped by everything else.

[David Parker]

Man, the fact that these tiny springs can just vanish into another dimension mid-repair is wild. Feels like every old keyboard hides at least one cursed piece like that.