How-To Repair Dead Lego Mindstorm LCD

Step 2: Repair

I replaced all three surface mount caps in my Mindstorm and still had problems return.  In my judgement, re-soldering / replacing the caps is a fool's errand.  However, I think goofing around with the caps inadvertently flexes the LCD ribbon cable and gets the LCD working again (for a while).

The real fix is to repair the ribbon cable.  The ribbon cable is held to the PCB with glue.  Overtime, the stiff ribbon cable pulls away from the circuit board and bad connections develop. 

The fix involves using your thumb to rub hard over the the ribbon cable to circuit board interface.  Rub hard on both side to reestablish / reactivate the bond between the ribbon cable and circuit board.

I wish there was a better way to permanently attach the ribbon cable to the circuit board.  My fear is that the ribbon cable is simply going to come loose again, overtime.

Comments

[BS Kustomz]

i rubbed mine with the handle of a plastic X-mods screw driver and it works fine... FOR NOW lol better than it sitting there and beeping

[jimk3038]

Yep,

Mine died again. Crap!

There must be something I can over the old tape to hold it down better. Maybe some epoxy? Maybe a big wad of sticky-tack? Something?

The old tape is just shot.

[mstokes3]

I have just purchased some conductive tape from Digi-Key for an exorbident price. Here's the link:
http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=M970312-ND&x=10&y=15
When I receive it, I'll test it. I'm pretty sure it'll work (based on the spec sheet). I'll let y'all know. I apparently have several to fix here.

[jimk3038]

Will the tape not short the contacts on the board?

The issue, seems to me, is that the existing tape is not holding the mylar ribbon cable down onto the circuit board. Even when the existing tape is reattached it tends to up up again.

I'm thinking of adding a ball of blue-tac right on top of the existing tap. Mushing the case down onto the tac will add pressure onto the existing tape / ribbon cable. The hope it that this will force the combo down onto the circuit board. Only problem is latter opening the case. The blue-tac is going to pull the tape away as the case is opened.

The blue tac is not the best solution - I just can't think of a better one. And yes, my display went dead again too! Gotta find a solution before school starts again.

Tough problem to solve,
Jim

[mstokes3]

Actually, no. The tape is only conductive in the Z dimension. The particles of conduction are spaced far enough apart to allow tracks with a minimum distance of 0.4mm. There are a lot of tracks but they are guaranteed to be separated by this distance. Time will tell. I'll let y'all know.

[phoppel]

Any word yet on the tape? If it works, I could sure use some to repair an NXT brick for the school Lego League team.

Thanks, Pat

[jimk3038]

I'm not have any good luck either.

My Lego Mindstorm LCD seems rather dead.  If I push / pull on the display just right I might get it working for a few seconds.

Turns out the tape is just a protective cover. Messing with the tape is just a way to flex the internal ribbon cable, I'm guessing.

Have a look at the attached pictures.

Rather a poor design, it seems to me. See how the ribbon cable makes a really sharp bend? Not good.

I did find something that might be a drop in replacement. Have a look at this:
http://wandisplay.en.alibaba.com/product/202533550-200851330/productdetail.html

I put in a request for info. However, the rep is in China so communications is difficult. Kinda at my wits ends. Might just end up buying a new unit.

Good Luck,
Jim

[luca_crema]

Hi,
any news about this approach?

[jimk3038]

I wish I had good news. However, my Mindstorm display is now totally busted. Worst, I can't find a replacement LCD anywhere. I'm dead in the water.

I did workup the nerve (since my NXT is dead anyway) to pull some of the protective tap off the ribbon cable. Attached are a couple pictures showing the exposed ribbon cable. Notice how the ribbon cable must make a super sharp bend around the plastic LCD housing. I think that is the failure point. If I ever replace the ribbon cable I would first cut some relief into that plastic.

Fooling with, and replacing, the surface mount caps, I think, just flexes the ribbon cable and gets it working again for a short while. I don't think the caps really have anything to do with the real problem. I now believe the root cause of the problem is in the ribbon cable since I can get the display to work (intermittently) if I hold the display just right.

I guess I need to workup some more nerve and pull the ribbon cable off completely. The problem is, I don't have any replacement ribbon cable either. So, once the old ribbon cable is removed, I have nothing to replace it with. Oh, and as you can see in the last picture, the ribbon cable dives into the rubber coating on the LCD.

I'm kinda waiting on mstokes3 to tell us how his tape worked too.

Jim

[luca_crema]

the daughterboard seems very simple but the schematic does not show the LCD part number; it seems a 12-pin lcd, while the "alibaba" part you were looking for is 14-pin (from the photograph)

as you see in the documentation LCD is 100x64dots 26x40.6mm area
3V supply + 9V driving voltage 

http://mindstorms.lego.com/upload/contentTemplating/MindstormsOverview/otherfiles/2057/LEGO%20MINDSTORMS%20NXT%20Hardware%20Developer%20Kit%283%29_7A0CF630-CCE5-4AAF-91FA-D1E7C911817C.zip

clearly, by replacing the LCD with the same part will only pospone the problem in time....

we need a "lateral" engineering idea

luca

PS: flexing the ribbon cable I myself can fix or get the problem , just like you did; the problem is really not in the soldering

[jimk3038]

I think I did find a replacement LCD - note, I did this search a while ago. I found this LCD at a Chinese manufacture ans I sent them a request for more information and got the an email back from them.

I've added a new "Step 5" to this instructable that has the attached PDF drawing that they sent to me.  So, look for the new step in this indestructible for the PDF.

The attached PDF shows the same pinout as the NXT. The problem is, their minimum order amount is 3,000 pieces!

Anyway, good luck with your NXT display,
Jim

Lisa - Formike [e-mail]
Sep 7 to jim.kemp, Burtton

Dear Mr.James,

Nice to meet you. This is Lisa from Formike Electronic Co.,Ltd.

Thank you for your inquiry.

Attached the drawing for your reference. Please help to confirm whehter can meet your requirement.

By the way,would you help to confirm the quantity for your inquiry? It will be our big pleasure if we have opportunities to be on service of you in near future.

Looking forward to your reply.

Best regards,
Lisa Huang Oversea sales manager Sales & MKT Department

Formike Electronic Co.,Ltd. | www.wandisplay.com Room 14H, HanKing Building, 23# DengLiang Road, NanShan District, ShenZhen 518054, China. P: [phone] Ext:809| F: [phone] Email: [e-mail] | [e-mail] Skype: formikelcd05 | MSN: [e-mail]

[luca_crema]

"If I ever replace the ribbon cable I would first cut some relief into that plastic.":

I'd try this, since there is a particular pressure point on the ribbon cable that makes everything work perfectly.
Please did you find it easy to remove the LCD from the plastic housing? Any advice?
Luca

[jimk3038]

Oh yeah, just pry the LCD glass up. The glass is held down into the plastic housing with two pieces of double sided tape. Don't be shy, once the tape starts to give way the LCD will come up free and easy.

The tape holding the LCD down is reusable too. Setting the LCD back down on the tape reactivates the tape. Good as new.

Good luck,
Jim

[luca_crema]

Jim,
looking better at the way to cut the plastic and back to the flex, I found that I have a different case than you, perhaps.

And I could solve the problem with a nail.

I tried to draw a sketch and upload it.

If you can see, it's better for me to explain.
The tape "invites" the flex ribbon to make a curve AGAINST the plastic.
The super-sharp bend is done "wrapping" against the PCB (down direction) and then curving upwards against the plastic.
With the nail I could push the tape to avoid the "super-bend" as you called it.

And now it works.

Probably one has to but something to avoid the superbend...

Luca.

[luca_crema]

Figure with a proposal (tiny roll of paper ? ) in blue.

Luca.

[jimk3038]

Wow, fancy fancy stuff. Didn't know tape like that existed. It does sound expensive. Still, if it works that would be great.

Yes, please let us know how you make out.

Thanks,
Jim