LEGO NXT Brick LCD Fix

As is well known, LEGO Mindstorm NXT bricks are prone to display failure over time due to degradation of the data ribbon that connects the LCD to the PCB. The data tape is called "Heat Seal Connection" or "HSC". I was unable to find a replacement with the required specifications for the NXT module (1.2mm pitch and 12 tracks). There are several procedures to repair this defect, most of which use a conductive adhesive to glue very thin copper wires onto the LCD connection pads. Here we are going to look at a solution without the use of such adhesive or the need for the manual operation of gluing the wires to the pads, which requires great precision and pulse. The solution is based on a simple 3D printed part that clamps the wires against the LCD in the position of the pads.

We will need the following:

• 3D printing of the part clip.stl
• 12x 0.2mm diameter copper wires 2cm long

The first step is to prepare the display and PCB by removing the adhesive data ribbon between the two. The PCB side is easily cleaned with isopropyl alcohol. The display side is covered with a silicone that we will remove by scraping carefully to avoid damaging the pads and we will finish by cleaning the remains also with isopropyl alcohol.

We start by printing the enclosed part in the Supplies section. Although it is easier to print horizontally (like it is the one in the above picture), it is best to print the piece vertically in order to give the plastic injected by the printer more structural strength to function as a clamp when inserted in the LCD screen.

The 12 copper wires must pass over the printed part following the path indicated in the section shown in the schematic image above.

To facilitate the fastening and to prevent the threads from moving when we place the clamp on the screen, we will apply epoxy resin on the upper and lower part of the piece. The piece of cable that remains inside the clamp will be the one that is clamped by the piece against the pads of the LCD display.

Now we adjust the clamp to the screen, making sure that the cables are aligned with the pads on the screen. We fix the piece in position with a couple of drops of epoxy resin. If correction is necessary, the epoxy resin can be easily removed from the glass.

As shown in the third photo, we cut the copper wires so that they protrude a couple of millimetres from the edge of the smaller glass that is glued to the larger one of the sandwich that makes up the screen.

Aligning the PCB with the smaller glass of the display sandwich, we solder the copper wires onto the PCB pads.

As you can see in the pictures, to do the soldering we will place the screen under the PCB turned with the face down.

The final step consists of folding the two pieces that connect the two cables (LCD and PCB) so that they are in the position that corresponds to their final arrangement on the white plastic piece that holds them inside the brick.

In order for the shield and PCB to fit into position in the plastic part, the copper wires will need to be shaped, which is not difficult as they are thin and malleable.

After checking if the display is working, reassemble the unit.