Tek 4109 terminal

[Jules Richardson]

On Thu, 2005-05-12 at 22:11 +0100, Tony Duell wrote:
> > Minor problem, in that I found the keyboard's pretty hosed. It uses
> > metal foil circles for the switch contacts; these are attached to the
> > switch plungers via foam spacers which give he correct clearance and
> > presumably help with the keyboard's feel...
> > 
> > Unfortunately it's the same stuff normally used for fan filters, and has
> > totally decayed :-( 
> 
> Ah, a Keytronics keyboard.... and alas I know the problem well, as the 
> keyboard on my PERQ 2T1 has suffered :-(.

Rats - first time I've come across it, but I suppose our 2T1 is going to
suffer at some point too!

> When I get a round tuit, I think I should make some kind of cutting punch 
> and stemp out 100 or so foam circles to fix the darn thing.... Or if you 
> find a quciker way of doing it, let me know...

Well at the moment I did a quick-fix using cut squares of that draught-
excluder strip that you put around doors to seal them. It's sticky on
both sides of course, with foam of about the right thickness, so is a
reasonably good match. I've only done the worst-looking keys though, not
all of them. Using squares rather than circles doesn't seem to be
causing a problem so far; whether it'll stand up to regular use is
another matter.

I did try a bit of foam cut into a circle first just as an experiment,
but it looks like getting the right glue there would be tricky (to avoid
the glue soaking into the foam and making it go solid)

> It's capacitive (not contacts). You'll discover the conducting layer is 
> on the _top_ (foam-side) of the lower plastic disk, and doesn't actually 
> short anything). My experience is that a finger placed on the pads 
> provided enough extra capacitance to simulate a keypress...

Aha, interesting. Explains why my trick of shorting pads with a
screwdriver to simulate a keypress didn't work! :)


The terminal seems to run self-tests ok, but I haven't found a RAM test
yet. The random crashes / power-up problems could be a whole host of
problems I suppose (I'll put the PSU lines on a 'scope too and check
there isn't something funny going on there...)

When it works, it looks like quite a nice beastie though...

cheers

Jules