Electronic Alarms and Home Security Devices - Ademco Vista 10: 1 key doesn't respond

I have a Ademco Vista 10, 1 key (3) doesn't respond anymore. how can I fix this? how do I take apart the keypad?

What happens, is that, over time, skin oil and other assorted gunk gets behind the keys and dries into a non conductive varnish.

You will need to power the panel down, remove the face of the keypad from it's back plate (with most models there are a couple of slots on either the top or bottom edge that inserting a small flat screw driver will release the face. Be gentle, this type of plastic becomes brittle as it ages).

Holding it face down, there are a couple of plastic clips that hold the PC board in place. Press them enough to release the board. The keys should stay in place. They are on a one-piece rubber membrane. The little ovals where the keys make contact are the source of the trouble: you will see that some of them have a dark coating . Clean them off with a q-tip dampened with rubbing alcohol, also clean the dark patches on the back of the keys.

Put everything back together and power up again.

This is really about a 60/40 shot. Sometimes the gunk actually damages the circuit board, and all you can do is replace the keypad.

how do i power down the panel? I can go into the panel. I see a circuit board w/a battery attached. On the circuit board is a line of connections. which 1s do I disconnect? are the power lines live?

It runs on 16vac. Just unplug one of the battery terminals, and unplug the batterypack screwed to a nearby outlet, or trip the appropriate breaker, or remove the wire on terminal #1. Restore power in the opposite order.