On 12/11/2014 15:36, Gareth Magennis wrote:
"N_Cook" wrote in message
...
I liked the potential booby-trap of the interboard connector, don't
remember seeing that type of breakable union before.
I was surprised how clean the contacts and pcb pads were. I'll go with the
single fine blonde hair looped under the octave silicone sheet, though not
directly over the pads when I got to them , it was looped around the 2
affected key positions, melded to the outer flange of the silicone. The
pads , moving and static and diodes,traces etc all test as expected,
otherwise. alance of probabilies goes with hair. It would be quite an
achievement to fudge up a conductive pad replacement. The stepped
arrangement of paired pads would not be a problem but that very squashy ,
ie thinned silicone , of the pedastal of each pair would be next to
impossible to work-around, I assume they can split at that place , with
heavy use or over time.


Hairs, usually animal, are a common cause of failure here.

I might have seen one or two splits in my long time repairing these, but
usually the contact patches wear out long before they start disintegrating.
It is quite easy to split a perfectly good one when removing it from the PCB
though, if you grab the "pedestal" instead of the more robust edges.

Some (Roland) are quite tightly held in place with oversize conical silicon
barbs pushed through holes in the PCB, most just have interference fit
silicon cylinders that push into holes in the PCB, which usually have a
small hole in so you can use the wire from a ceramic power resistor to push
them fully home.


Gareth.



If a 50 micron hair is enough to block a function, it looks as though
the moving contact pads are too hard. I wonder if they harden-up with
age or use.