Unknown XT dome board TEBD-0014 [silver reed domes of some sort]

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zrrion

05 Nov 2021, 05:15

Been waiting forever for this (and a few other boards that I'll be getting to here in a bit hopefully.) Got it because it was an XT layout board with what looked like topre/topre adjacent mount.
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To cut a short story a bit shorter: these suck, the domes are stiff, weakly tactile, and mushy and the caps are not topre compatible.

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here's a picture of the back. it was actually shipped with the flip out feet extended and I'm surprised that it wasn't damaged. It looks rough, but it would likely clean up well enough.

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Caps are nice and thick doubleshots. They're stepped but curiously also have simple rod stabs as well. not really sure why bother when it's stepped but in nice condition I don't doubt that they would make the switch more stable.

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Now, I knew it was a possibility when I got this that it would be related to the silver reed typewriter module I already had and as it turns out they are. These use the same slider and the caps are made by the same place. (the 2 caps on the left are from the XT and the 2 on the right are from the typewriter) but the profiles do not match. the XT caps are taller.

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and a really clever way of having in switch LEDs on a membrane board, sandwich the leads of the LED between a piece of conductive rubber and a pad on the membrane, then there's no need to solder. Unicomp could learn a thing or 2 here.

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brass screw inserts are an interesting thing to see here but I guess as thick as the caps are here they might not have cared overmuch about cutting costs.

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and for all the size these have there's not much going on inside.

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Here we have the slider/dome comparison. Silver reed on the left, XT on the left.
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you can see how dusty these are but also how short they are. they're slightly shorter than the silver reed ones and boy does short travel low tactility, high weight, and high mush combine to make a very bad switch.

if you want to see another board using the same switches and caps haata has one here: https://www.flickr.com/photos/triplehaa ... 325443066/

CallmeJohn

16 Nov 2021, 07:48

It seems that a board I own uses the same keycaps but with completely different switches. https://imgur.com/a/JnNKh3N mine came with adapters for these assuming Jelco made skcc clones, the larger keycaps also use a pole for stabilizers.

User avatar
zrrion

16 Nov 2021, 08:51

That's super weird considering the Jelco switches are a lot taller than these domes, odd choice to pair them with these caps then and doesn't help at all to explain the relation of these caps/switches with previous silver reed stuff.

Never heard of those switches before either but I suppose that's one more thing I can add to my list of things to try.

lee4hmz

02 Jun 2022, 10:40

The matrices in this board and the one linked toward the end seem to have been made by the same mysterious "FK/FKJ/JFK" OEM that made the Coleco ADAM keyboard and some of the TRS-80 Color Computer keyboards.

lee4hmz

16 Jun 2022, 06:32

zrrion wrote:
16 Nov 2021, 08:51
That's super weird considering the Jelco switches are a lot taller than these domes, odd choice to pair them with these caps then and doesn't help at all to explain the relation of these caps/switches with previous silver reed stuff.

Never heard of those switches before either but I suppose that's one more thing I can add to my list of things to try.
Okay, I think I have a lead on this!

In my last post, I mentioned that some of the CoCos have keyboards with "JFK" model numbers, Well, I found pictures of the inside of one at https://www.leadedsolder.com/2019/12/06 ... -rust.html, and in particular this picture:

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These look a lot like the switches described in the '378 patent linked on Jelco's page in the wiki. Given that, I'm pretty sure at this point that the "J" in "JFK" means "Jelco". It seems like a lot of OEMs used Jelco back in the early 1980s (seemingly when they couldn't afford Mitsumi or ALPS). I don't know exactly yet how this relates to Silver Reed, since they built their own keyboards in several cases, but it's something.

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wobbled

16 Jun 2022, 17:44

Getting topre vibes from this board from those sliders

lee4hmz

17 Jun 2022, 02:55

Jelco and Topre are/were both based in Sagamihara, so there's a possibility that they're either directly related or shared some personnel. I imagine the documents that'd bear this out are all in Japanese, though.

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zrrion

17 Jun 2022, 06:10

Yeah, if this is Jelco then that might be a lead for not only these domes, but for the other dome switches that silver reed used that were not din compliant but that will be hard to figure out since the documentation is likely in Japanese. I can try trolling around google patents some more though and hopefully something comes up

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jsheradin

17 Jun 2022, 15:08

The beard has some good info compiled about Jelco including a definitive tie to the JFK series: https://telcontar.net/KBK/Jelco/

Seems that there's some patents available in Japanese along with paywalled mentions of them in old engineering journals.

User avatar
zrrion

17 Jun 2022, 23:57

beardsmore's page is good, but primarily deals with jelco switches that are recognized by the branding on the membrane whereas I'm interested in dome over PCB switches that they likely made. It looks like most folks who got the mystery switches that I suspect are jelco made chose to have their names on the PCB which is not helpful. Membranes being (I assume) harder to manufacturer than a PCB did not get rebranded so the trail is easier to follow.

lee4hmz

18 Jun 2022, 04:25

The thing that sticks out about the JFK domes, to me at least, are those 4 notches on the bottom of the dome, as shown in this picture I took of the ADAM domes a while ago: Image

I've seen that particular dome design in several other places, and I also think there's a conductive-dot version of it as well.

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