Tatung VT-4100

[Tora]

Hi all.
I've been following this forum for a while but this is my first post.

I have this old Tatung VT-4100 terminal and decided to take a closer look at its keyboard.
It has spherical double-shot keycaps and what look like some old mechanical switches.
Anybody know what kind of switch this might be? I've browsed through the wiki but found nothing that looks like it.

The caps are pretty dirty. I washed off the dust but I they're still yellow. Any tips on how to get them to look new again?

I love these old-school keyboards. Thinking about getting in on the group buy to replace the caps on my Filco.

Tatung VT-4100 keyboard

IMG_20131117_181412.jpg (468.43 KiB) Viewed 1812 times

Tatung VT-4100 cap and switch

IMG_20131117_181511.jpg (364.22 KiB) Viewed 1812 times

[Muirium]

That question mark! Sweet, oldschool font on these caps! The one you've upturned looks a lot thinner than a Honeywell, or indeed Round 5. But it's high hat (the middle is raised, like on many old IBMs) so 7bit probably still likes it. They've still got a good texture, too.

The discolouration is probably yellowing rather than just dirt. These are doubleshots, so they're ABS, and ABS is the number one plastic for turning yellow in ultraviolet / sunlight. The underside of the caps should still be the original colour, because it's out of the light. Looks like they weren't white anyway. In any case, Retrobright is the only way to undo yellowing on ABS.

[Daniel Beardsmore]

Anybody know what kind of switch this might be? I've browsed through the wiki but found nothing that looks like it.

Exactly! It's quite similar to various switches but not actually the same as anything I can think of. The best thing to do is to open up the case and take a look inside — sometimes the switches and PCB are made by the same company, and you might have the OEM name written on the PCB. There are also clues with the shape of the switch, and the count and arrangement of the legs.

(If it comes the worst, you might need to desolder, remove and open up a switch to see what's inside of it. Some switches had a wide variety of exterior designs, such as ITW Magnetic Valve, but those should at least have a characteristic leg arrangement.)

[Tora]

I opened up the case to get a better view.
The PCB is also manufactured by Tatung. The switches have 4 legs arranged as a square.
They have a square shape and there is a round slider on top. Between the sliders and the switch is a metal plate. Although I wasn't able to remove the top slider, it seems like that should be possible.

Strange thing about the caps: the letters of the RETURN and ALPHA LOCK keys are not yellowed. So maybe there's supposed to be a difference in colour, or they used different plastics.

Tatung VT-4100.jpg (789.35 KiB) Viewed 1728 times

IMG_20131201_152436.jpg (653.23 KiB) Viewed 1728 times

[Daniel Beardsmore]

Plate mounted and with four contacts? That's unusual — usually you only see the extra contacts in PCB mount switches. Neat looking PCB, too.

[HaaTa]

Neat!

I've never seen a switch like this before.
By the keycaps I would have guessed Alps switches.

The PCB traces are a bit odd (some leading to nowhere it seems), seems to indicate a built in diode (or just anchor pins) rather than something like magnetic valve (which requires two loops; i.e. 4 pins).

It'd be awesome if you could desolder a switch, and attempt to take it apart :D:D

[webwit]

Switch case looks a bit like old futaba.