Novag Aquamarine RISC II 26.6MHz
Second repair

Whit this unit, I decide to make a more radical repair, removing the old sensory membrane and creating a new one.

I start by removing the sensory board using hot air. Care must be taken not to damage the top film. The rest can be discarded.

This repair is based on a very simple idea: to reproduce the sensory board in a handmade way. The complication lies in the limited space available for its housing.

The operation of such a matrix is very simple and can be understood with the following diagrams:

If we press on D2 square, column "D" is short-circuited with row "2", it's as simple as that:

Therefore we have to create the following structure, where the conductive tracks are shown in red, and the spacer "insulating" foil in black:

And, due to the limited height available (less than 1mm), I decide to create a sensory board with the following layers:

Approximate measurements.

I use materials I have at home:

  • Aluminium adhesive tape, the kind they sell in hardware stores.

  • Double-sided adhesive tape.

  • Cardboard.

  • Adhesive film (such as Aironfix).

  • Cyanoacrylate glue (such as Super Glue).

  • Enamelled copper wire, the kind used in coils.

We start by cleaning the machine, removing the old adhesive, and then drilling 1mm holes through which the copper wires will pass:

The metal plate is covered with adhesive film:

I use Aeronfix, the adhesive film I use to cover books.

Metal plate now covered. The aim is to insulate it electrically.

Now I make the 16 adhesive aluminium tracks, 10mm wide:

NOTE:

  • It is very difficult to solder copper to aluminium using tin. It can be done but with a special flux, a high-power soldering iron (with the risk of burning the adhesive), etc. It would have been much better to use copper tape (see Third repair), but I didn't have any at the time.

  • The enamelled copper wire is very convenient to use, but obviously the enamel covering it has to be removed from the areas we want to connect, solder, etc.

  • I decided to "solder" the copper wire to the aluminium with silver paint, coating it afterwards with cyanoacrylate. The result was satisfactory: good conductivity, very strong bonding, etc.

I conducted stress tests...

We hold the 16 aluminium strips on a piece of wood, and then solder 16 copper wires:

We cut 16 sections of copper wire with a diameter of 0.4mm

Silver paint is used and left to dry for at least 1 hour.

We have now 16 aluminium strips with their respective copper wires.

We then coat the silver paint with cyanoacrylate, which will give it the necessary strength:

And we proceed to install the 8 strips of the rows on the base of the board:

The copper wires are fixed at the bottom with the glue gun:

The spacer sheet is prepared from cardboard (of the same thickness as the original plastic spacer) by cutting out 20mm circles:

Once the spacer cardboard is finished, double-sided adhesive tape is stuck on the areas not occupied by the row tracks, i.e. parallel to the rows. Then remove the protective paper, turn it over and stick it on:

Note that the cardboard has been trimmed at the edges to leave space for the soldering, both on the left (rows) and below (columns).

Detail of the space left for the row solder joints.

Now we prepare the tracks for the columns, which will be glued on an A4 sheet of transparent plastic:

The transparent plastic sheet is cut to size, and marking the margins of the tracks with a felt-tip pen.

We remove the film and stick double-sided adhesive tape on one side, then cut off the excess tape.

On the left the plastic film with double-sided adhesive tape on its underside, and on the right the 8 prepared aluminium tracks.

The aluminium tracks are attached to the plastic film on the upper side.

Double-sided adhesive tape is attached to the spacer cardboard in the areas that will not be occupied by the tracks of the columns, i.e. parallel to the columns.

Remove the paper from the adhesive tape on the cardboard, insert the copper wires through the holes provided for this purpose, and carefully attach the film of the column tracks.

The copper wires of the columns are fixed with the glue gun, as we did previously with the rows.

Finally, the top film is conditioned and attached:

All old adhesive must be removed.

With alcohol and patience. Do not use solvent!

A few hours later.

The surface is completed with double-sided adhesive tape, cutting out the pieces where the buttons, LEDs, displays, etc. will pass through.

Removing the protective paper from the double-sided adhesive tape.

And then came the most delicate moment...

Try to attach the top film correctly. This is not easy.

We can now mount the motherboard, and connect the sensory board to it:

Work completed!

Ex-post considerations:

  • Conductive tracks: it is better to use copper tape rather than aluminium because of the ease of soldering with tin.

  • Cleaning: although acetone is ideal for removing old adhesive, care must be taken that it does not damage the plastic. It is safer to use alcohol.

  • Wiring: instead of enamelled copper wire, plastic-sheathed wire can be used, but it will have to be really thin.

  • Row and column separator spacer: it would have been preferable to use plastic instead of cardboard, as the latter is easily damaged.

  • Finish: the screen-printed top film, which contains the squares, the names of the buttons, etc. is surprisingly thin. It should be noted that it is very likely that some marks will remain visible.

  • Conclusion: a viable repair, but a very laborious one.

Take a look at this revised method: THIRD REPAIR