LK451 keyboard needing work

[g1l1t1]

I have an LK451 (word processing) keyboard with Ps/2 connector. I bought it cheap and hoped to get it fully working, but ran into two problems I can’t surmount without parts or some serious ingenuity.

1. Someone spilled something (a cola drink, I suspect) into it that ate away several of the traces and contact pads on the two printed-circuit flexible plastic sheets that make up the key switches and wire up groups of them to the encoder circuitry.
2. On the elastic sheet with raised domes that serve as the key “springs”, several of the domes have been completely crushed. They won’t stay in place if you try to press them back up.

I can’t imagine that either type of damage could be repaired or mitigated (but just maybe someone can prove me wrong) so I’m hoping to find replacement parts somehow.

The keyboard layouts differ between the LK411 and LK451, but I don’t know how the inner workings may differ. Perhaps they use the same plastic circuit sheets, but if so, the encoder logic must differ. I can imagine how the same elastic spring sheet could possibly be used if the keycap posts line up the same, but who knows?

If you happen to have unneeded parts for the LK451, or nonfunctional units that could be scavenged, or some othe source of parts, , please let me know. (I’m not hopeful.)

 

[Alegend]

If your LK451 insides are similar to a LK402, then it is easy to fix corroded traces. I have posted the details of such a repair I did here: https://microvax2.org/wp/2017/05/24/lk402-aa-keyboard-fix/

As to the crushed domes - that sounds like something that is beyond repair. Apart from salvaging a replacement from a better-shape donor keyboard.

-Alon.

 

[Terry Kennedy]

As to the crushed domes - that sounds like something that is beyond repair. Apart from salvaging a replacement from a better-shape donor keyboard.

On low-profile notebook keyboards, replacement keys come with individual rubber domes cut from a donor keyboard sheet. I wonder if the same thing would work for the DEC LK4xx keyboards.

Eons ago, I worked for a typesetting shop that was also the US rep for the company that produced the typesetting system. The terminals were Lear Siegler ADM-2 units. The keyboarding people were very highly prized because of their speed (100+ WPM typing marked-up book text from copy) and accuracy, and they were to be humored At All Costs. Since this was the late 1970s, that meant tolerating them smoking and getting ashes in the keyboards. The stock ADM-2 keyboard used circular aluminized mylar discs on the bottom of foam pads, which did NOT work well when ash got in there. I designed replacement keyboards that used a pair (for redundancy) of sealed reed switches for every key, and replaced the foam plungers with magnets to trigger the reed switches. Since there was no foam pad left, the plungers needed helper springs to lift the keys back up. I had a variety of springs made up so each keyboardist had exactly the feel they wanted. Micro Switch made a run of 100 or so of those keyboards. Unfortunately, I didn't keep any of them.

That was one of 2 keyboards I designed for typesetting applications. The other was a "true Selectric" keyboard - it matched the size / shape / sculpting / feel of the IBM Selectric 2 almost flawlessly - the only concession was the Return key and neighboring keys, to add extra keys present in ASCII but not on the Selectric 2 keyboard. One of the more fascinating features of that keyboard is that Shift Lock (a true Shift Lock, not the usual Caps Lock) is a mechanical latching key that can be released by pressing either the left or right Shift keys. That drove the people at Micro Switch nuts. I don't think they ever did one of those before (or since). It also used my double reed switch design, as you can see in the second picture below. Oddly, I never got any pushback from Micro Switch about potential patent infringement.

I wouldn't quite say that "cost was no object" at that company, but they did things like having Kodak grind a custom lens for the Kodak Ektaprint 200 copier (in itself an amazing piece of equipment that filled a small room and copied 200 originals per minute and never jammed or damaged originals - way better than contemporaneous Xerox offerings) so it would make true 100% duplicates. Most copiers enlarged slightly so there would be no shadows from page edges on the copies, but when people are staring at copies using a loupe with calibrated type height grid lines, it is 100% or nothing.

Unfortunately, with the offshoring of keyboard manufacturing it would take way more than 100 units to get any company interested in making a custom design these days. If it were possible, I would have designed a LK46x replacement years ago, when HP discontinued them. My idea was to have every key be fully programmable, with the USB connection being a hub with a HID device (for the user keystrokes) and a serial port emulator (to receive / send commands for key definitions and other stuff).