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Thursday, February 24, 2011

Repair a Malfunctioning LCD - Hack a Day

Repair a Malfunctioning LCD

heatgun

When most people encounter dead pixels on an LCD text display, they figure that the display is dead and they decide to scrap it. However when the LCD display on one of [Joe]‘s cordless phones started to show dead rows and columns of pixels, [Joe] decided that he could fix it. With only a pencil eraser, a hot air gun, and a screwdriver (for disassembly), [Joe] was able to fix his phone’s screen in just under 10 minutes. His process involves heating the glue holding the LCD’s ribbon cable to the phones PCB with a hot air gun and using a pencil eraser to reattach segments of the ribbon cable to the PCB. If anyone here has a problem similar to [Joe]‘s, be sure to check out his detailed how-to complete with step-by-step pictures.

tagged: diy, hot air gun, instructable, lcd, repair, ribbon cable, screen

Reader Comments

Hot-air-repair fails to often to do on your own stuf. Rather do this with the iron for ironing shirts. The blow-gun is likely to wreak havock in there.

Posted at 2:24 pm on Jun 20th, 2009 by Ivan

@ivan

this is why you need to be easy on the trigger so to speak. Patience and knowing when to ease up on the heat will make this a lot easier. plus it should be easy in the first place because the paste they use for flex cables like that melts way sooner than solder or many of the plastics. this is probably why these displays tend to have issues in the long run, due to the low melting point. all you really have to do is pay attention to what your doing and this shouldn’t be any harder than soldering two wires together.

Posted at 2:31 pm on Jun 20th, 2009 by sly

Joe:

Thanks for the tip! Just this week I had this exact problem come up with a calculator. I’ll be trying this right away. But using my new Aoyue Hot Air Rework Station which I bought on the recommendation of Hackaday. :-)

Posted at 3:43 pm on Jun 20th, 2009 by gyro_john

Good idea, I don’t think I would try it though, I’d probably cross over all the connections. :P

Posted at 3:44 pm on Jun 20th, 2009 by Roon

Just done it last week but i havn’t used an hot air gun, just added a small piece of paper to give a better pressure betwin the ribbon and the screen :s (but it work :D)

Posted at 4:43 pm on Jun 20th, 2009 by _n3o_

If only I had known that a few weeks ago.

My MP3 is now in pieces in my shed…

Posted at 5:20 pm on Jun 20th, 2009 by Sammy

I just use the tip of my soldering iron. A piece of paper or thin cardboard can help spread the heat and force.

Posted at 8:13 pm on Jun 20th, 2009 by Greg Jones aka übermeister

I have a laptop with screen lines, would you guys reckon placing the screen in an oven would fix it?

Posted at 8:57 pm on Jun 20th, 2009 by PoorKid

@Gyro_John: Be careful with the aoyue, mine caught fire because I had the fan on low and the heat on 320.
@poorkid: I doubt it. Laptop lcd’s are sealed in a plastic-y casing and hooked in with a solid jack. To even get to the ribbon cable would render the screen useless, at least on HP-compaqs. Try checking on ebay, chopshops usually have replacement lcds super-cheap.

Posted at 12:30 am on Jun 21st, 2009 by St.Jimmy

Great tip !

I’ve just fixed 2 of my 3 cheap DECT phones that all suffered this problem.

The third one still has characters missing, maybe I’ll try to heat it one more time later…

Posted at 1:05 pm on Jun 21st, 2009 by Cri

that is seriously awesome. thanks for the tips!

Posted at 1:41 am on Jun 23rd, 2009 by Louis II

Thanks for the tip, I tried on my scientific calculator which was about to get dumped due to this LCD problem. Problem is not solved 100% but yes I would say 90% digits on screen are clearly visible now. Still calculator is useless but this trick works!

Posted at 12:34 am on Sep 16th, 2009 by Hashim

Thanks for the tip! My calculator is working now!

Posted at 3:18 pm on Nov 2nd, 2009 by Janie

While I can understand the inspiration here,
this really isn’t the proper way to repair a
heat seal connector.

First the conductive anisotropic adhesive used
is typically thermosetting rather than thermo-
plastic. Meaning you will have limited to
no success functionally re-plasticizing it via
heat. Even if you do succeed to soften the
adhesive of the defective connection you’ll
also be doing so to the adjacent connections
as well given the broad stroke of the heat
gun being used.

The principle by which anisotropic conductive
heat seal adhesives function is to create an
electrical connection between surfaces via
microscopic conductive particles embedded in
the adhesive base. These conductive particles
are either fully metallic or metal plated
glass/plastic forced into conduction between
surfaces under tension established by heat
set of the adhesive while the joint is held
under pressure. This is usually accomplished
during manufacture via a resilient hot bar
fusing device which holds the entire joint
under pressure until the adhesive has set.

By reheating such a broad area there is risk
of relaxing unintended adjacent conductors as
well causing them to fail. While the above
technique may well succeed in some limited
scenarios, it can as easily do more damage than
good. Particularly given the low mass of the
flex cable and the unregulated output of the
heat gun.

The typically recommended technique to repair a
defective heat seal connection is to heat the
joint and remove the entire flex conductor,
solvent remove the remaining adhesive on the
mating glass/flex surfaces, apply a new film
of anisotropic adhesive, *accurately* realign
the surfaces, tack them in place temporarily
(a modest temp soldering iron will do here) and
re-weld the joint with the above hot bar
mechanism.

That said, if the household hot bar fuser isn’t
available I’d recommend trying more localized
heat + pressure to repair the failed connection.
I’d avoid the use of hot air altogether as it
is difficult to control where the heat is being
applied in this case. Rather I’d place a small
metallic object such as a bare metal thumbtack
head-down over the suspect joint ideally
separated from the flex cable by a scrap of
paper. Heat the exposed underside of the tack
with moderate heat from a soldering pencil and
keep the tack moving and pressed against the
flex. Initially the adhesive thermosets is the
150*C ballpark so you don’t want to exceed this
by too much otherwise the risk of degrading (or
outright melting) of the flex cable exists.
Once the tack is up to temperature I’d remove
the heat and keep the tack in pressure and motion
over the joint. You can grasp the stem with a
pair of tweezers to do so. I’d recommending
starting off conservatively in terms of heat
and retry with increased temperature if the
initial attempts fail to reestablish the joint.