DIYbanter - telephone, push 'pad' repair; electrolyte?

"2apart" wrote in message
...
I am repairing a Panasonic wireless phone. It has a molded silicon
push pad which contains all the phone's buttons. Behind each 'button'
is a small black deposit which, when the button is pressed, contacts a
pwb land. There is, was, a gel coating on the board. I didn't know
if it was crap from the kitchen or an electrolyte; something that was
supposed to be there. What is it, and where can I purchase the gel...
if indeed it isn' t old food? (Yup, I cleaned it off, and now the
phone buttons don't work at all) Thanks.

I used to repair many tens of cordless phones every month, including
Panasonics, and I have never seen any deposit between the conductive rubber
pads on the keymat, and the PCB contact area, which should be there. OTOH, I
have many times seen a deposit such as you describe, which *shouldn't* be
there. It is usually caused by partial chemical breakdown of the conductive
rubber material. In most cases, it is actually quite hard for external
contamination to get between the keymat and the PCB. Generally, the keymats
and PCB can be recovered by a firm treatment with a cotton bud (Q-Tip)
soaked in electronics grade isopropyl alcohol, but you have to be careful
not to be too aggressive with keypad PCBs, where there are tracks and
contact points layed on by deposition of a conductive paint. You should be
able to test that the contact points and the keymatrix scanning all work, by
bridging individual button locations, with a small piece of aluminium foil.

Arfa