Need help rebuilding a "butchered" NXT brick!

[jobu1234]

First off, hello to everyone on this site! I'm new to the Mindstorms (and Technic) Lego kits, and I'm looking forward to a lot of fun exploring new projects and this site.
I found an NXT 1.0 set at a garage sale for a deal (basically free) because the NXT brick is damaged. The seller tried to "pimp" (his words!) the LCD by replacing it with a bigger one. Unfortunately, he stopped mid-pimp for some reason, just after completely removing the original lcd from the board driving it! Nothing is working on the brick as far as I can tell (because the speaker is also disconnected) but i hope the brick might be functional if I can reattach the LCD. Considering that most of the other pieces were still in their plastic bags when I opened the box, I don't think this NXT set has actually even been used!

From what I googled having to do with NXT LCD repairs, the lcd screen is normally connected by some kind of mylar ribbon with traces on it. In MY case, the ribbon is gone, the daughterboard has a bunch of thin gauge wire leads soldered where the ribbon connected, and the LCD is bare. Cleaning the LCD where the ribbon would connect, I saw what looked to be faint traces directly on the glass. You actually can't see them except at certain angles so they're pretty insubstantial. If I were to try to reconnect the LCD to the driver daughterboard, does anyone here know what I can use for a ribbon? I'm pretty good with soldering, but I don't think that skill's useful here with the glass. Maybe something more like a conductive epoxy?

I guess I should try to reconnect the speaker first to see if I can even get a heartbeat from the poor little guy. I'm just wondering if the LCD is a lost cause before I get started. If so, I guess I can always get another NXT set and use all the other parts from this one with it.

Thanks for reading!
John

[mattallen37]

Hi, and welcome to mindstorming and this community!

I would reconnect the speaker, and then call it good enough. I personally wouldn't try soldering or gluing wires to an LCD, but what's there to lose? You can use a program on your computer to view what the LCD is supposed to be displaying, so the LCD isn't a must. Getting another set (or just another brick) would be a good idea, as "you can never have enough Legos!"

[jobu1234]

Thanks for the reply. I reconnected the speaker, and I get the startup melody when I put batteries in, so that's a good sign!

If I can find some conductive glue locally, I think I'll give the screen repair a shot tomorrow. The LCD traces look nice and big... under the right light, that is!

The "traces" are only visible in reflection from the glass


And if it doesn't work out, maybe I can score another NXt kit as a holiday gift. As you said, "mo Legos, mo betta!" (ok, I'm paraphrasing! )

[h-g-t]

It might be possible to find an edge connector with the same spacing, then solder wires (hard drive cable?) onto the connector pins.

Probably wouldn't be able to fit all that into the case though so you would have to mount the lcd externally.

http://www.in2connect.uk.com/edge_card. ... 4QodNwG0pQ

[jobu1234]

Thanks for the great suggestion! I measured the trace width & spacing the best way available to me... via photo
I cropped/scaled this pic to a 0.75" width/1600 ppi, measured from the approximate (eyeballed) center of the ruler marks (1/32").

Using this unbelieveably precise measurement method, I found the trace width and spacing to both be approx 0.024", or about 0.61mm

So center-to-center contact spacing would be 0.048" (probably actually 0.05" since that seems to be standard)

The trace spacing and glass thickness (0.05") seem to be within the range for using one of these connectors. I'm not sure about the connector depth though. The traces are 0.075" long, and the shallowest connector depth I saw was 0.300" for ISA cards. If I can find a shallower connector or a way to support the glass in this one, I might give this a shot. I may even have one of these connectors lying around. hmmm

I also ordered some conductive adhesives to test. Got "wire glue", which seems to be graphite-impregnated rubber or silicone cement, and another compound to fix surface mounted components. I don't know what's in that one, but I figured that the main application for it implies that it's pretty low resistance stuff. Should arrive just in time for me to play with it over the Thanksgiving weekend here in the U.S.

[mattallen37]

That's great news! Please be sure to keep us updated.

[jobu1234]

Say hello to my little friend...


The conductive glue route worked beautifully, though it was definitely a trial to put all the delicate pieces together. Anyhow, here's what I did:

The glue I used is called "Surface Mount Component Fix" (I call it SMC glue here) made by a company called Anders Products . Here's the action shot:

You actually need to pour off the top layer of solvent when you first use it, and then stir it back in until you get a good consistency (think Thanksgiving gravy thick). It can get a little messy, which is why it looks like I had 10 cups of coffee before opening the jar... well, I actually had 3 or 4 come to think of it.

Like it's sibling product, Wire Glue, it seems to use graphite for conduction. However, the resistance is much lower, at least in my testing. Since I ordered both products, I painted a line of each on paper, and measured resistance at 1mm distance (between probes) when they dried, The Wire glue was 3K ohms (!) and the SMC fix was 200 ohms. Wire Glue MAY have worked for this, but the SMC fix seems a safer option.

So I painted the LCD leads with the SMC fix, using a toothpick as a stylus. I actually whittled the end of the toothpick with an xacto blade to get a finer (0.5mm roughly) point. I also dipped an end of each wire in the glue and let that dry (about 15 minutes). Basically, I "tinned" the wires and pads, to use soldering terms. Then, I dipped the wires in the glue again and placed them on the LCD pads. I found tweezers to be useful here since the wire is 30 gauge and approx 1cm long and the pads are only 0.5mm apart. I actually did slip on one wire and wound up bridging two pads with the glue. Fortunately, it was easy to scrape a channel between the pads after the glue dried, using a fine-tipped xacto blade.

I let the SMC glue dry/cure for about 6 hours, and then added some 2-part quick drying epoxy on top to protect the connections. The SMC glue is pretty brittle and would not hold up on its own to any wire-bending stresses. I let that cure overnight.


Next, I trimmed the open wire ends to a reasonably even line and then soldered them to the LCD driver board. In the pic, the lcd screen is face down, and covering the NXT keypad contacts.


Next, I (carefully) bent the wires back, rotating/lifting the screen until is was visible. (Here's where the epoxy reinforcement is key.).
Time for a system check....


With the screen working, the last thing to do was to finish bending it into position, which is basically 180 degrees from where it started.

As you can see in the picture, the fit is pretty tight. The keypad needed a little finessing to get it seated under the wire.

That was basically it. The biggest pain in this fix was the wires - I went with solid-core because that's what I had in my supplies but I think if I did it over again, I'd try some stranded wires...maybe even some ribbon cable like that from an old IDE hard drive.

Now on to the important stuff... ROBOTS!!

[mattallen37]

Wow, I certainly wouldn't have tried doing that, despite understanding electronics and being able to solder. Very nice job, and thanks for posting about it!

[h-g-t]

Magnificent work!

[mightor]

Wow, that is very cool Not for the feint of heart, it seems!

- Xander