What is this black adhesive that connected a foil ribbon to the PCB, and how best to repair?

Thread Starter

bobtiki

Joined Feb 29, 2016
3
A little context: I am trying to restore a Casio PT-7 keyboard, and the biggest issue is that the keyboard has stopped working. As you can see in the photo, the keyboard is a smooth flat surface, there are foil layers inside, and pressure on the keyboard triggers a key press.

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Opening the very thin keyboard up, the culprit appears to be that the adhesive holding the connector from the foil keyboard to the PCB has gotten brittle with age, and the ribbon of foil contacts are no longer connected to the PCB surface.

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As you can see in the photos, the contacts on the PCB are not bare, but are covered in black, what I am currently assuming was the adhesive. The interesting bit is that if I hold the foil connector back in position with, say, a piece of weatherstripping foam and a clamp to provide even pressure, the keyboard does work again. I suppose I could try to repair the keyboard by making that foam/clamp situation more permanent (and in fact, I know one other person that has repaired their PT-7 keyboard in exactly this way), but I would love to better understand how this connection works, and repair it in a more permanent way.

Could anyone please enlighten me as to what this black adhesive might have been? Might it possibly be carbon or graphite impregnated in some way? I find it odd that the black extends across the entire pin area, and isn't just on each individual pin, so I expect it can't be that conductive, or it would short all of the pins together. I'm as a bit of a loss as to how this connection works, as it's something I haven't come across before.

Any recommendations on the best method to repair this connection would also be very welcome. Thanks!
 

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MaxHeadRoom

Joined Jul 18, 2013
21,208
Typical Key push for many objects have ferrite looking conductive surface that often either gets worn or dirty over time, you can get replacement pads on line for this type on line.
Not sure it this will cure your problem, but often a polish with contact cleaner, the Type that doe not leave a residue can sometimes cure it.
Max..
 

Thread Starter

bobtiki

Joined Feb 29, 2016
3
Typical Key push for many objects have ferrite looking conductive surface that often either gets worn or dirty over time, you can get replacement pads on line for this type on line.
Sorry, but I'm not sure I understand your reply. This ribbon connector isn't a key pad itself. It's supposed to be a permanent connection.
 
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