14 Jan
2008
14 Jan
'08
6:51 p.m.
I seem to have my share of Terminals that have bad keyboard parts.
3 that I'm working now have the same type of Keyboard. These
are Hazeltine 1500 and ADM 3As. These have an molded base
with fingers that stick up and a second square piece that slide into the base
and makes and breaks the finger contact. It also has a square opening in the
top for the key cap. So when someone drops a heavy object on the the key board
this intermediate piece cracks in the corners and binds in the base.
I know the design well. The contacts spring togethe, and are kept apart
by a plastic pin in the plunger when the key is not pressed.
The keycap is a press-fit into the plunger, which means it slightly
stretches the latter. In time the plunger cracks anyway, even if you
don'y drop anything on it.
The other prolem is fitting new contacts. At one time you could buy
individual contacts and more importantly a tool to hold them and press
them in place without damaging them. Said tool was (at least) sold by
Radio Shack Nationl Parts Centre and HP (I have part numbers for both),
but AFAIK it's now unavailale, It's possilble to use long-nose pliers
carefully, but it's very easy to mangle the contacts.
What I would like to find is a doner type of system that does not have
any value so I can rob the middle piece.. (typewiter) ???
I've seen this type of keyswitch on (at least) the following :
DEC VT50 series
DEC VT100 series
TRS-80 Model 1 (early version only)
TI 99/4a
HP80 series (HP85, etc)
HP9915 keyboard (very rare!)
HP98203 (small keyboard for the HP9816)
HP2623 (IIRC) graphics terminal
Unfortunatley none of those are exactly common. When I repaired my 9816,
I was lucky enough to find a 'spare' VT52 keyboard PCB i nthe junk box,
given to me with a load of other DEC spares, which provided contacts,
plungers, even keycaps.
-tony