Restoring a Casio Ca-501 - help needed

[albertofenini]

ciao a tutti,
I'm about to restore a CA501 recently purchased.
The module is working, but the front panel is missing.
I have found a nos front panel which I'm about to receive in the next days.
I started to clean the module, since the keyboard was not responsive at all.
Differently form other CA from Casio, the keyboard is a multiplexed sistem,
like in some of the calculators.
The pressure of a key, cause the underlying structure to generate a single
combination of contacts that thru a zebra strip will go to the module.
As a matter of fact, passing the zebra with a tweezer, gently, will make
the module behave like the keys were pressed.
At first, I have cleaned the zebra with cotton and alchool and some of the keys
began to work.

IMG01660.jpg

IMG01661.jpg

IMG01662.jpg

As it can be seen in the pictures, the keyboard is made of several pieces.
We have the rubber keys, just mechanical action, no electrical conduction.
The yellow strip, adhesive, that is the first thing that goes into the case
against the keys (from the inside). The the white one, the side with the continuos
strips will go toward the adhesive layer and the keys, and represent the row
contacts.
Then the trasparent layer, double side, than the zebra and the module.

When I have cleaned the transparent plastic layer a lot of dirty came away,
but I'm worried that it was more graphite, than dirt. Does anyone has done this before ?

Now, I can only get the keyboard to work if I put the two layers directly
on the module but out of the case, looks like when the keyboard is in place
again, the zebra is not pressed against.

Anyone has a suggestion ? Can I keep cleaning the layers ?

Thanks again for help, Alberto

[digibloke]

Hi Alberto.

With Calculator pushers and buttons that work outside of the case but not inside it often tends to be a positional problem with the module. The older Casios have a small lip of plastic at the battery end of the module which sits on a ledge in the case. This holds the module in place to within a fraction of a millimeter so that both the side and front buttons make contact. This thin bit of plastic sometimes gets shaved off when the module is removed from the case meaning that the battery end gets pushed too far in when it's replaced.

You can remedy this with the older C-701/801's by glueing small bits of card (business card thickness) to the bottom/front of the module (taking care to stay clear of contacts/buttons etc). I've never tried it with the newer keyboards like yours but it could be worth a try.

[albertofenini]

ciao Digibloke,
thank you very much for the tip, I will give it a try but the lips (upper and lower) are both in good shape.
I'm more afraid that cleaning with alchool the pcb ans stripping it in two pieces has probably damaged it.
I have found a NOS spare part also for that and I will order it.

Meanwhile, the keyboard faceplate has arrived the rubber keyboard has been all cleaned and the glass has been polished, this is the result :

IMG01673.jpg