In particular; take my Vtech gigaphone. This phone, like the others in the house, has a large flexible membrane which implements the unit's push buttons. When the phone was new, a soft, quick touch successfully entered the number. Now the keys require a long steady pressure before the phone senses the push.
I opened up one phone and removed the membrane. It has black colored (carbon?) conductive (I think conductive) backing material just under each button When the button is pushed the black areas contact lands on the pwb. I cleaned the unit using just water but it didn't help.
Is there some kind of dielectric paste or conditioner which must be reapplied? Must the carbon contacts be specially rejuvenated with some chemical?
The lands on the pwb are clean.
How can this be fixed?