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SWTPC TVT2 Under Repair

Okay well.. that was the world's shortest problem. I don't know what I did (pressed in the connector super tight) but now it's working. At least, locally with Echo ON. I'll try with a terminal later.

If you have any thoughts on key repair/replacements anytime let me know Chuck. I can't see a way to get these buggers apart safely and get in there.. and even if I could I doubt I could get them back together again.
 
I believe that I posted a link to some Cherry key switches before--if you buy them in quantity, they're pretty cheap. At any rate, they should be a close match to your keycaps, but lower in profile and the leads come out closer to one side. They might be worth experimenting with, since you can buy them in quantity one.

Cherry switches are very, very good and known to the gamers.

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Thanks!! Yeah I'll have to have the authenticity debate with myself soon.

Do you know if the original keyswitches were SWTPC's own design? Maybe I could find something close if I knew who the real maker was.

Thanks for all your help. I just plugged in a terminal and verified the serial card is communicating correctly. 40 years old and still working!
 
No, I doubt that the keyswitches or key caps were designed by anyone at STPTC. When this thing was new, there were lots of makers of keyboards--and keys were most often assemblages of discrete parts. Keytronic was very big (it was later acquired by Honeywell), George Risk made some of the best--and still does--they've been in the business for more than 50 years. Microswitch was in the business as well.
 
How do the key switches mount? i have a bunch of NOS switches for Ohio scientific keyboards, put them in the 70's at least

G
 
I finally figured out how to get them apart. They have little holes in the bottom - if I stick a small multimeter probe up here and push firmly, I can pop it out. Here's what came out:

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Here's the inside of the base:

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I'm not really clear on how it works. The bottom of the spring assembly appears to have a little bit of a groove where the wire would go.. and inside the base there's only one alignment that wire could sit on. So I assume pressing down causes the wire to bridge the gap between the two poles. But I don't understand how it travels back up.. there's nothing attaching it to the bottom of the spring? I'm thinking I must be misunderstanding how these work. If I can figure it out, they seem simple enough that they could be rebuilt. I'm looking into the base there and it looks like the two poles may be kind of stuck together or corroded or something.
 
Neat.. I got both keys to work again!

Seems to be:

Tap switch poles gently. The switch poles form a sort of candy cane shaped hook. The long end goes through the PCB to be soldered, the top hooks into the plastic of the switch housing and then the ends rest more or less flush with the bottom of the key switch base with just a small gap between them (I think, can't really see). You have to make sure they aren't misaligned with one hook end or the other slightly out of position.
Put slight bend in copper wire, carefully place it in the only slot it fits in (diagonally) and make sure the ends rest on the little 'shelf' inside.
Put the spring with its 'hooks' aligned with that wire over the square shaped plastic in the center of the key base. (There's a small piece of foam at the top.. no idea what that's for).
Put the top on very carefully and then snap in. Test with ohmmeter -- voila!

Worked on both. I'm not *really* sure how it works or what I'm doing, but I've found a pattern that sort of works so I'll take some more dead keys out and see if I can get them to live again. I'll need to find out what gauge that copper wire is so I can get a piece for the key that flew apart.
 
Strange that it's bare copper wire--that would corrode with time pretty quickly. I wonder if it's not phosphor bronze--looks like copper, but it's considerably harder and "springier". Model railroaders use it Sample. Some musical instruments use it also--I've got a harpsichord full of the stuff, along with brass and iron wire.
 
That may well be what it is. It's quite a bit harder than what you'd expect. I just assume it was copper. Wish I understood how it all worked. I have 9 more keys that need reviving. And I need to find a replacement piece of that stuff to replace the one lost in my broken key.
 
Well.. it took two weeks but I 'rebuilt' 14 keys and it all seems to be working! Pretty exciting! Almost kind of spoils the thrill of my TVT project, which will display the same thing and do more or less the same thing, less the extra memory page and serial board.

Anyway, as it turns out.. the only things wrong out of the gate were the power supply and a coupe of stuck keys. Special thanks to Chuck for helping out and patiently explaining RTL, power etc. Now I have three working CT1024s!

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