SOL-20 keyboard question

[Tony Duell]

>     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