K-256 Revisited

I had a note down to take the cover off the Unitek K-256 that I’d previously blogged about, in order to take a picture of a keyswitch.  Well, it didn’t stop there.  Five hours later, here I am.

I think it was worth the effort, because now I have a flawlessly-performing and very clean keyboard as a result (I was rather surprised at how clean the inside of the keyboard was- actually one of the cleanest I’ve experienced for its age).  What I found when I went into the keyswitches though…

First off, the ESC key and the numeric numpad minus keys did not work.  So, I gingerly released the four clips, two on either side of the switch, and pulled the top cover off.

I discovered that the metal leaf that makes contact with the other metal stub was tweaked just enough to where it wasn’t making contact when the switch was depressed.  Fortunately I was able to straighten out the leaf without removing the keyswitch (which would have been no big deal, but if I can avoid it I will).  As you can see in the picture above, the plastic slider normally keeps the leaf and the metal “stub” separated; when the switch is depressed, contact is allowed and the keypress is registered.

I’d been told by José (XMIT) that these switches were “Taiwan Jet Axis.”  Indeed, they fit the description.

Having conquered the ESC key, I focused my attention on the minus key.  Not being as accessible as the ESC key, as it is right next to the asterisk on the numeric keypad, I had to find just the right tool that would permit access to the latches between the two keys.  This bent pick thingy worked a charm.

What I found when I got the switch open was a little more complicated – and discouraging.  At first, I thought it was just another bent/tweaked leaf.

But then I realized… the leaf had no leg to it – the metal extension that sticks down through the switch housing and through the PCB.  Somehow it had sheared off and was still stuck in the housing.  I was very ginger in the removal of the leaf, so I’ll just have to assume it had been hit hard at some point in its life – or … something.  Who knows!

Well then.  I desoldered the leg from the PCB and pulled it out.  Then painstakingly paired it up with the leaf and soldered them back together.  This took a couple of tries, as any residual solder on the leg of the leaf would cause it to bind on the house hole, twice causing it to again shear off.

I finally got it though, and to my relief worked.

There was also a paper mat laid down under all of the keys, and I’m not quite sure if that was just for appearance sake or if it had a function such as noise deadening or PCB protection against mild liquid spills or something.  If someone knows, throw me a comment, please.  I did not put it back in when reassembling the keyboard, as I thought it might be interfering with the actuation or giving the keys a weird feel and frankly didn’t see the need for it.

Looks to be a 1991 model?

Now that it’s all clean and works properly, I can take a bit more pride in it and enjoy using it.  The actuation force still bugs me, though.  I remeasured again and still came up 60g +/-5g.  There is no way in hell I would have guessed that this has a lighter actuation than my K-260 with linear green clones that I measured to be ~65g.  So the reason they feel so stiff is still a mystery to me, and I’ll just have to chalk it up to the different switch mechanisms.

Interestingly enough, not all of the sliders were the same color.  Some were a much more pale yellow.

If I had to come up with a description of how the keys sound, I’d say that it reminds me of when a large piece of chalk hits a sturdy blackboard.  It’s an interesting “thock.”

Before:

After: