28 Dec
2005
28 Dec
'05
6:59 p.m.
They look like they should be mylar coated or
silvered Kapton discs
with a foam backing. The foam is mostly decayed, and there's virtually
no silvering left on any of the discs. They few that do have only the
This sounds like a Keytronics capacitive keyboard. The disks are
assembled silver-side up (away from the PCB), they don't actually make
contact. But when you press a key, the conductive metal on the disk
increases the capacitance between the 2 pads on the PCB.
Failure of these assemblies is, alas, well known. There are 2 problems --
the first is that he foam decays, the second is that the metalisation
goes. It looks like you've got both at once.
At one time you could buy replacement disk/foam assemblies and they were
quite cheap. Then the price skyrocketed, then they became, I believe,
unavailable. Pity, as I need to re-do a PERQ keyboard sometime soon (same
design).
-tony