Repair of electronic tracks on a keyboard: conductive liquid silver

Repair of electronic tracks on a keyboard: conductive liquid silver
In this entry we will repair a keyboard of CNC which are no longer manufactured
The contacts of the keyboards have evolved from mechanical systems, to the most modern membrane. In this case we are going to repair an intermediate type; This keyboard of a lathe Geminis FAGOR 8050T 15 years carries a membrane silk screen Panel of aluminium for tracks and graphite for contacts, on which a piece of metal with flexible concave shape closes the contact pressing.
Switches the keyboard technology tends to be of two types;contact, where some kind of dock (metallic or plastic or flexible rubber, etc) keeps separate tracks on the surface conductive (graphite or other material) key, that pressing une tracks; and on the other hand, those of induction, where when the button is pressed, a small magnet creates a small electrical impulse in the coil of the membrane (durable ultra modern musical keyboard).
Repair this type of keyboard tends to be complicated, and requires all your "handyman" skill; some with copper tracks as TV remote controls tend to be easier to repair welding on the tracks a small micro switch if the button is completely disabled, but most cases are membranes of plastic that can not be welded and can be used either to stick threads on them as in this tutorial, or to use the useful liquid silver.

Necessary material

  1. Cutter to open the damaged contact (in another type of keyboard is not necessary).
  2. Liquid cleaner or solvent which does not attack the material of the keyboard; I've used Ardrox 9PR5.
  3. Conductive liquid silver, with which "draw" deleted/damaged tracks with a fine brush after clean them well.
  4. A tester to check the track drawn conducts electricity.
  5. A pair of scissors, PVC tape for back cover contact, brush, indelible marker to draw back the key, etc.

The contact that had to be repaired was severely damaged from both to be used; the ENTER of the numerical control lathe, so I extracted the metal piece another keyboard unusable by cutting the upper part of the plastic guard with care; We can see the tracks and the thin layer of graphite into contact in good condition; sometimes simply with clean contact (without scraping to not delete the graphite) very carefully and replace back to work:

We do the same with the contact to repair; we are going by cutting plastics with care not to cut the tracks, and we see that the graphite is practically erased; as we will replace it with the conductive silver, we will not repair when cleaning with a cloth and cleaning fluid to clean visible tracks free from grease and impurities.

Take extreme care not to erase the tracks; they are extremely thin.

By opening you can see the tracks, separated by a green paint to insulate them:

This conductive silver Kemo, with glass of 3 g. of silver powder jar, is very good conductive (between 0.02 and 0.1 ohm per cm2), depending on the amount. As you can see almost all of the vial is thinner (only 15% of the content will be Silver).
The conductive silver helps to repair the anti-fog circuit tracks in the rear window of the car, and in general to repair electronic tracks of membrane.

The trick that I use to make sure I leave a good amount of silver with the brush, is beat the little boat and let 5-minute stand with the CAP downwards; Thus it accumulates in sufficient Cap amount, and upon opening it I use the amount deposited there.

We give a first coat carefully to not join the tracks, and let dry thoroughly:

We give a second coat, and once dry (takes about half an hour), we check with tester that conducts electricity well and also not have gathered contacts, playing in the different points of the circuit. If it does not give good conductivity in some area, remove that part of paint, clean and return to apply:

It will be to put together the outer race through the center point when the contact closes

We finally put the metal button and check that it works with the tester and press contact.

If everything is ok, we will proceed to cover with adhesive tape; I've placed the first thin clear tape, and then a couple of layers of white PVC tape to give durability, I painted the original text and have again put tape transparent to protect the text and that is not erased by hand so easily.

Keyboard repaired
I took advantage to protect another pair of keys used in the lathe began to occur (once the protective plastic breaks, start to get fat and failing), with some PVC tape, painting the text and another layer of transparent:

And already it can be placed in the machine, to last another 15 years;). Happy repairs!