>> For 102 and 200 -- But the 102 keys are silicone domes with graphite pads
>> and metal contacts on the pcb.
https://youtu.be/n_oyDYRDYzs
These type of silicone springy domes had a 'carbon pill' glued to the bottom. A
carbon pill is silicone rubber mixed with carbon black to make it conductive.
Sometimes this type of contact can just be cleaned with alcohol and all will be
well. The rubber can also oxidize, the silicone rubber can also leach silicone
oil and they can suffer from external contamination as well.
If cleaning with alcohol does not work, you can soak them in a mild alkaline
solution like household ammonia or a mixture of 1 teaspoon of sodium hydroxide
(lye) to 100ml water. After soaking them and letting them air dry it is a good
idea to soak several hours in 99% alcohol as the rubber can become saturated
with liquid. I did a video about this method: https://youtu.be/n9gGz2n-sBU
This is a similar contact often used on remote controls that has a very thin
layer of conductive rubber painted onto the bottom of the keys. This wears off
very quickly. Most of the commercially available solutions you paint on either
fall right off or wear off in a few months. I tested a few of these paint on
solutions and only found one that really worked well. The 3D printer keypads I
fixed in this video are still working fine 18 months later:
https://youtu.be/XInxW0YtghY
Jeff Birt
