Sinclair ZX80 / ZX81 / Z88 Forums

Found an old Zedy in my junk pile that has a keyboard that was never mounded but has damaged lead ends. One end is cut off and the other is folded where it probably cannot conduct electrons. Can the conductors be re-exposed?

Sadly there's no reliable way to repair those ribbons..
If they are broken near the end you can trim them and hopefully they are not too short but the material is brittle and probably will not last long..

If replacing with a new one is not an option for you... one way is to desolder carefully the connectors from the board, use some ribbon cable prolong them from the board to the remaining keyboard membrane.

But a new replacement is probably the best way

As said above, I’ve seen the membrane PCB connectors relocated to the top of the case and glued to it, then flexible conventional ribbon cable wired from these to the PCB.

Mark

I was hoping some could provide a method to remove the plastic covering from one side of the ribbons to exposed the conductors of a shortened ribbon.

jsweinrich wrote: ↑Thu Jul 08, 2021 2:44 pm I was hoping some could provide a method to remove the plastic covering from one side of the ribbons to exposed the conductors of a shortened ribbon.

Do you mean inside the keyboard??
Those tracks are not easily repaired... silver paint is useful:useless::50:50 and expensive.. I ve seen some one to sew them with thin copper wire.. not reliable ...

jsweinrich wrote: ↑Thu Jul 08, 2021 2:44 pm I was hoping some could provide a method to remove the plastic covering from one side of the ribbons to exposed the conductors of a shortened ribbon.

You cut off the damaged section to give a nice clean edge, then carefully peel the layers apart. Then cut off a further section of the plastic only part. If you still have the plastic stiffener section from the cut-off damaged section, use this with the part that has the conductor tracks when inserting the tail into the PCB connector. But don’t try to use glue, as most glues have solvents in them, which attack the plastic ribbon.

Mark

jsweinrich wrote: ↑Fri Jun 25, 2021 3:54 pm Found an old Zedy in my junk pile that has a keyboard that was never mounded but has damaged lead ends. One end is cut off and the other is folded where it probably cannot conduct electrons. Can the conductors be re-exposed?

Why not just buy a replacement keyboard? There are people manufacturing brand new ones.

Thanks all. Although I developed a great method to connect to the trimmed ribbon cables using conductive adhesive copper foil my keyboard was damaged inside... So, yea, I ordered one...

jsweinrich wrote: ↑Tue Jul 20, 2021 3:10 pm Thanks all. Although I developed a great method to connect to the trimmed ribbon cables using conductive adhesive copper foil my keyboard was damaged inside... So, yea, I ordered one...

Would you share it with us?

Here it is in a nutshell. I trim the ribbons even. about 2" from the keyboard. Using a paper towel I then apply denatured alcohol to the side of the ribbon that is not the plastic carrier. I found that one side seems to have a removable coating. Being careful not to rub to hard or long. You can check your progress by using s ohm meter along the ribbon trace. You should also check to see if you are rubbing away any silver by holding the ribbon up to the light. If there are places you can see through then you have rubbed to much.

I then cut a blank PC board the width of the two ribbons and a bit more covering 1.5" of the ribbon's length. I then drill holes that line up with each ribbon trace for wire attachment. I then epxoy the ribbons to a blank PC board, one on each side as the two ribbons are opposite with the bare traces facing out. I then cut thin strips of 3M adhesive conducting copper foil tape and apply along the entire length of each ribbon trace and onto the PC board for about an 1/8". Make sure to rub them down to get proper wetting. I then prepare two wire type ribbon cables (could use regular wire) to go from the PC board to the Zeddy PCB. One cable goes into one side of the PC board and the other opposite. I then solder the wire to the 1/8" foil pad the is on the PC board. Other end of the wire ribbons solder into the Zeddy PCB, remove keyboard connectors first. BTW, I did have to cut the hole in the case larger to fit the PC board through.