VT52 keyboard question

Tony Duell ard.p850ug1 at gmail.com
Tue Mar 14 01:30:00 CDT 2017

On Mon, Mar 13, 2017 at 8:45 PM, Marc Howard via cctech
<cctech at classiccmp.org> wrote:
> Hi,
> The "2" key on my VT52 is very hard to use.  You've gotta pound it and you
> might get 2 "2"s for your trouble.
> I assume that the keyboard switch is made of unobtanium (If you know of a
> substitute chime in) so I'm thinking of swapping it for the "COPY" key
> which I guess is useless unless you have the built-in thermal printer.

On the VT52s/VT55 that I've worked on...

It's actually not a separate switch. There's an single moulded frame for
the entire keyboard. Each swtich constists of a pair of contacts which
naturally touch, a return spring and a plunger that keeps the contacts
apart when the key is not pressed.

You can pull off the keycap. Often carefully cleaning the contacts (which
are then visible) will help. The plunger and spring pull out too, officially
you are not supposed to re-use the plunger but you have to now.

The contacts can be desoldered from the track side of the board and
pulled out. There was a special tool to put them back without damaging
them, it is possible (but tricky) to do it with long-nosed pliers. Avoid
removing the contacts unless you really have to replace them with ones
from another key or keyboard.

It's the same type of contact mechanism as in the early TRS-80 Model
1 and the HP85. The technical reference / service manuals for these
2 machines may be of interest.


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