Repair A Malfunctioning LCD

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.

43 thoughts on “Repair A Malfunctioning LCD

  1. @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.

  2. 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. :-)

  3. 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)

  4. @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.

  5. 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…

  6. 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!

  7. 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

    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.

    1. I have an idea – ho about first using a spring clamp ,grabbing both sides of the display connection thus exerting bonding pressure on teh conductive joint. Next use tin foil to mask off the areas you do not wish to get really hot. Finally, use teh heat gun lightly over the exposed tape. It seems that teh joint s would get hot and under clamp pressure they would re-bond. Once it all cools down, remove the clamp. Test. Move on


  8. I’ve been trying to find out how to fix my calculator LCD! This worked like a charm! THANK YOU!!

    I was prepared to spend the 50$ on a new financial calculator so I just tried this with a hair drier =D.


  9. i fixed two lcd displays today using a temperature controlled soldering station set to 350 deg. F with a 1/16″ chisel tip. just went along both connector rows constantly burnishing in an oval pattern. worked perfectly.

  10. Thanks for the trick! I just tried it on my cordless phone display and it worked like a charm. I just wrapped the tip of my cheap soldering iron in aluminium foil to help spread the heat + cool it down.
    It took 3 tries to have the display fixed.
    I found out one should slide the hot tip back and forth quite fast at first and slow down progressively to avoid melting everything…

  11. Have somewhat similar problem (or is it different altogether?) with (battery operated)LCD display used on a Cross-Trainer. Screen initially displays then goes blank after a few seconds. Any tips on cause & fix, please? Still works functionally – can hear graded acoustic beeps signifying levels of difficulty, etc. As I know machine well, am ‘blind’ programming it at present.

  12. When the LCD digits are visible, but fades away slowly, it’s because they are applied with a DC voltage, not an AC voltage, which they need. You should check for bad solder joints or a short on some of the timing components (a resistor or capacitor) which times the AC-signal applied to the LCD glass.

  13. Just tried something similar on a 1024×768 LCD monitor panel, the very right-hand vertical columns were stuck in various colors after I accidentally dropped the monitor. I found that pushing on the ribbons caused the problem to lessen or go away. I pulled out my SparkFun heatgun and applied heat to the faulty ribbon for 30 seconds to a minute at 2-5 inches away, slowly moving it back and forth. The columns are all fixed and the panel is perfect now. I also managed to fix the controller board that would randomly not start the panel on power-up (think it was a mis-seated ROM chip).

    1. No. There is no cable in a digital caliper. The display contacts the pcb trough a “zebra”-strip. An always-on segment can be one of two things – either the driving ic is faulty, or maybe the lcd glass has moved a tiny amount to the side, so that the contacts don’t line up Perfectly, and the connection for your always-on segment is connected to a neighboring signal. Try to remove the glass and clean the glass and pcb with isopropul alcohol, reassemble and see what happens.

      1. Thanks very much for that!

        Mine is actually a 12″ digital DRO scale — but very similar to a digital caliper. The LCD had a black conductive strip on it with tiny grooves at the top side which contact the PC lands. It was stuck to the glass, and I thought it was a permanent connector on the LCD — I couldn’t understand what you meant by cleaning the glass. But I eventually realized it was made of rubber and could be removed.

        There were barely visible conductive coating lands under it on the glass. So then I knew what parts to clean. Sorry to say, cleaning with alcohol and attempting to shift slightly didn’t fix the read-out — so it is probably the driving IC. Unfortunately the missing segment makes it impossible to tell a 5 from a 6 or an 8 from a 9, and that would be a big problem on my mill!

        I’m wondering if I can replace the whole sliding unit (or the circuit board) with one from a cheap digital caliper. The full scale would cost over $100 to replace, while 6″ digital calipers are about $10-$20 these days.

        Anyway, thanks very much. I now understand these displays better, and it was a good shot at fixing the problem!

        1. Good that I could help :-) Usually the circuit inside these DRO units is the exact same as a standard 6″ caliper, just observe the mechanical properties of the sliding strip etc. feel free to post a picture of the defective DRO, i’ll be happy to help you find a suitable donor.

          1. Fantastic! Thanks so much! Doubly happy ending:

            I remembered I had an old 6″ digital caliper that stopped displaying. I found it, opened it up and saw the identical circuit board and swapped it into the DRO scale body — retaining the DRO LCD and buttons. It worked perfectly.

            Then guessing that the 6″ scale LCD and contact strip had been dirty — causing its display blanking, I cleaned it and installed the DRO’s circuit board. Now it works as well, though still with the single segment problem.

            However, here it is much more acceptable. The digit affected is the inch digit, lower left segment always black. So there could be confusion between a 5 or a 6 inch measurement. But the difference is obvious — the 6″ caliper all the way open is 6″ — anything less must be 5″.

            It would be nice to blank that segment instead of always being on because it does make some other numbers look odd. Can I do that by putting a bit of tape over one of the contact bads on the PCB — or are the traces multiplexed in a way that would affect more than one segment? If not I’ll just cover the offending segment with something opaque,

            No matter what — I’ve now got two working tools out of two paperweights! Thanks so much!

  14. Hi Nick,

    My old Citizen calculator lost its second digit some weeks ago. So I decided to buy a new Lexibook calculator during my holidays in France but though I securely put it in a pouch + between my clothes, It did not appreciate the long travel (25h to Nouméa) and my brand new calculator had quite all its digits not functionning any more !

    I searched for tips & solutions over the web in french but found nothing at all. Research in english found your site at once and I could repair my old Citizen in less than 3 mn ! To tell the truth, I could not find anything comparable to your picture, so I used my hairdryer without any conviction at all and throwed some hot air on the cable during less than one full mn. There was no results, so I was about to end all operations when I saw that the ribbon cable was in a bad “shape”, kind of twisted.

    So I took a piece of paper and toll it to make made a small cylinder that I put under the ribbon cable before closing back the calculator and it works !

    Tomorrow, I’ll try to check my new Lexibook before throwing it away.

    God bless you and many thanks for your tips !
    Jibé from Nouméa

  15. The “BONDMASTER MANUAL.pdf” (a device for Motorola pager repair) reveals the following parameters of different HSC foil cables.

    Quote: “the pager bond time 1:45 has been factory set as a default and is recommended for most applications…”

    forces & temperatures:

    Planar = 50..70 psi at 140..150°C
    Anisotropic = 50..80 psi at 150°C
    Monosotropic = 70..90 psi at 160°C

    “Planar” cables (pitch 0.3mm, oldest) are yellow-black.
    “Anisotropic” cables (pitch 0.29mm, cheapest) are green-white or black-white.
    “Monosotropic” cables (finest pitch 0.22mm) are yellowish, with thermoset adhesive.

    I.e. the cable needs to be pressed into place during the heating and cooling cycle, which may take about 1:45 minutes. Depending on material, the heat can be between 140 and 160°C. Too hot may melt it, so try lowest heat first. The thermoset glue of “Monosotropic” (yellow) cables may be impossible to re-melt and so needs to be replaced.

  16. Genius!!!! Following your instructions, I was able to repair two old items, I did not want to throw away. Your method worked great! And, I am no repair expert. I took me 5 minutes to repair both items using your methods. Again, you are a Genius!! Thanks.

  17. Had some success with a broken iPad Mini screen showing intermittent black bar/half pink bar. This is a well known problem when the LCD is moved during a touchscreen replacement, and sometimes cooking it in a low FAN OVEN on the lowest shelf will do the trick. I’ve also used this method to repair laptop screens before as well, the trick is not to overdo it as this will melt the backlight and polarizer rendering your screen a paperweight.

  18. most of these are not “LCD” repairs since that refers to “liquid crystal displays” right?

    I have a 1990s zoom PS04 that has dead collumns after getting wet. I took it apart and let it dry for some years [forgot about it]. Now I am getting it going again and the display is comprised of the following: plastic window, plastic removable display panel, white plasticized paper and finally a white coating on the circuit board it rests on. Not 6 or seven like the wiki examples with polarizers etc. The white square on the board is fenced by left and right copper contacts and the voltage is passed to the screen by ‘zebra strips’ which are rubber rectangles made of segments that conduct but are insulated from the adjacent row by rubber blocks sandwiched together.

    I dont seem to need any of the oily coating since most of it is gone now so I am wondering how the liquid crystal is maintained ‘in’ or ‘on’ the plastic panel?
    If I clean the surface with a solvent will I remove the crystal or is it confined within the plastic sheet?
    I also assume the white papery or thin plastic underlay is for contrast and can be wiped clean yes?


    Now the display

  19. Worked great on an old Tech America soldering station’s LCD. I used a good hair dryer set to its high-heat/low-fan setting. Used the eraser on the back of a pencil to slowly push down on the ribbon. The flat ribbon cable seemed very fragile but it all worked out fine.

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