Re: Lisa Keyboard Repair - Here comes how to...

From: Dr. Helmut Post <helmut_post_at_email.domain.hidden>
Date: Sun, 06 Nov 2005 17:12:12 +0200

on 06.11.2005 13:56 Uhr, Philip Lord at philip_at_email.domain.hidden wrote:

> I have a spare keyboard I'd like to get going. There are maybe 10
> dead keys, and a few really sticky ones. what causes them to stick?
> P
> On Nov 6, 2005, at 7:36 PM, macmoni wrote:

Hi Phil,

the Lisa keyboard is totally different from other Mac keyboards- the Mac uses switches (Alps inc.) which can produce corrosion over the years, but not the Lisa keyboard:
The Lisa uses a 3mm-4 mm thick foam material ( as found in many candy packages/boxes or tool boxes etc...)
This foam material is glued to a small round plastic disc on one side to "snap" inside the key itself. On the other side there is a special metallic looking foil (like christmas paper)- this foil is not electrical conductive! Don't use any aluminium foil- this could ruin your Lisa keyboard. Recycle your foil pieces and reuse them again. As a replacement for the glue don't use fluid glue- this may ruin your keyboard- just use a sticky glue ( Pattex etc...) The foam material deteriorates over the years and forms a kind of sticky mess... this produces the sticky effects on several of your keys. The keyboard uses a "capacitive" concept- a switch is built from an aluminium pad on the PCB and the non-conductive metallic looking foil. If you press the key, the foil presses against the pad (under the pressure of the foam material) and forms a capacitor- this capacity change is translated into an electrical impuls. if you use fluids or pressured air, you can easily ruin your keyboard. You have to open it very carefully and reconstruct all key switches with new foam material. Don't forget to clean the pads on the PCB from sticky glue and foam smudge. The whole work took me a full afternoon- but if you completed your task you have a brand new fully operational keyboard.

Measurements with an Ohm meter is not possible- you can only measure a capacity change with a capacity measurement tool- but that is not necessary.

I have successfully refurbished 3 keyboards- they are fully operational now, and will be for the next decade...
there was no need to solder anything... only cutting foam disks- you can use Guido Deiana- he has successfully completed the same task as I did.


P.S.: Don't use any cleaning fluid!
This ruins all!

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Received on 2005-11-06 08:23:45

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