The fourth Google Nexus smartphone, released November 13, 2012.

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Touchscreen not working after display change

After dropping my Nexus 4 and breaking the front glas, the touch screen did not work anymore. I decided to change the full display unit (digitizer + LCD). I have now replaced the display unit with a new one and connected everything as it was before. Turning on the phone worked instantly and the new LCD shows a flawless starting screen. However, the touch functionality does not work at all. So now I'm wondering if I made a mistake in reassembling the phone or if the new display unit is defective. Is there anything I might have missed? Or is there a way to test if the problem lies with the display unit or the rest of the phone?

I should note that I got the new display from ebay and while it certainly is new, I assume it's not an original part. I also noticed that my old unit had some sort of shielding on top of the chip that is right above the digitizer connector, my new unit does not have this shielding...

Any help would be appreciated!

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Hi there. I've just had the exact same issue this evening. As I had purchased a glass/digitizer only in first place (which I couldn't manage to install without destroying the original LCD as it is glued to the digitizer), I was able to push the diagnosis a bit further.

-When booting with the LCD/digitizer assembly connected, the digitizer is totaly unresponsive. I suspected a flex cable damage or ESR damage to the digitizer chip, althought I am an experienced repair guy with all the proper equipment.

-I then turned off the phone, and swapped the digitizer connector with the Glass/digitzer I had purchased before, just to make sure the problem was not coming from the logic board of the phone. And the glass/digitizer worked fine.

-Now with the phone still powered on, I hot swapped the two digitizers, and the previously not working digitizer started working. It all stops working when you reboot the phone.

-I have double checked every connector related issues and tested continuity on all traces. Hardware failure is not the origin of the problem.

So my diagnosis is as follows : the digitizer chip provided by the manufacturer of these LCD/digitzers is not registering properly at boot with the kernel. If you put a properly registering one, the drivers will load up fine, and will be used properly with the "defective" digitizer as long as they stay loaded in memory.

I have a 4.4.4 Kitkat, I have looked several places on google to find any low level trick to fix this driver issue but could not find any real solution. I have contacted the seller on ebay (elife-tribe) to address the issue and to know if they are aware of the problem. I'll keep you updated of any further development.

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Hi philippe, that's very interesting! If this is indeed a software problem, I'm sure these digitizers were supported in some previous Android Kernel. My phone is on Android 4.4.4 as well. It's a long shot, but you could try to install Android 5 using your spare digitizer to see if the newer Kernel supports the digitizer in your "defective" display assembly.

I got my display from a different seller (judyhk05) and even though I just contacted the seller 24h ago, I receieved a full refund via Paypal already! I'm pretty happy with that service. However, the fact that the seller didn't even ask for details and apparently doesn't want the display unit back either hints to this being a known issue. If I can indeed keep the display, I will try to remove and replace the digitizer. That should be a lot easier when the display is not glued to the phone chassis. Where did you get your intact digitizer? I'd hate to run into this problem twice...

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Hi Janus. I got a first typical and kind reply from the seller asking to clean contacts with alcohol, and not open a case against him ;-) The seller is elife-tribe on ebay. I am expecting another reply offering a replacement part in the next 48h or I'll escalate straight to Paypal for a refund.

I have conducted more tests. My faulty digitizer is actually recognized in CWRT Recovery, and the key test shows that it properly sends command to the phone, but when Android loads, it just fails to load the drivers. I have confirmed that when booting with the working digitizer, then hot swapping with the faulty one, everything works until next reboot. It is either a wrong soft Identifier on the chip, or a faulty response of the chip to the initialization routine of the driver. I have had a close look at the chip and surrounding parts. These Chinese digitizers use cloned versions of the Synaptics S7020A chip, but they seem implemented differently. The working digitizer has 3 ceramic decoupling caps and 1 resistor, while the non-working one also has an extra diode for a total of 5 SMD components around the chip. Still the Synaptic chip shows the exact same reference number (very poorly engraved). Also the working digitizer has the 4 SMD parts aligned on one side only (the side toward the connector to the logic board of the phone), while the non-working one has 5 SMD parts on two sides of the Synaptic chip. This may be useful when purchasing a replacement on ebay. Also the working digitizer has a flex cable showing a mesh array of conductive traces underneath the chip (likely to offer a better RF protection), while the non-working digitizer has a normally etched flex cable. I have already glued this silly assembly, now I am heading toward more hours of fun playing with glass shards... I'll keep you updated.

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I forgot to mention that I also spent few extra ours upgrading to Android 5.1... Doesn't change anything unfortunately...

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Hi again, I can now confirm that we are having identical issues. I just received a new digitizer and it works fine in combination with my "defect" display assembly. When I hot swap the digitizer connector after booting up the phone, the touchscreen of the "defect" display assembly suddenly works as well! I have also looked for a software solution to this problem (I guess the correct firmware might do the trick), but couldn't find anything. It feels so stupid to solve this issue by peeling of the digitizer from a perfectly fine display assembly and glue on another one just to solve a software problem...

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Ugh, this is so frustrating! I decided go for it and removed the digitizer from my new display unit. Unfortunately, it looks like I broke the LCD in the process. So now I have two digitizers (one with a software bug though) and no intact LCD. The worst part is, I couldn't find any LCD only offers on ebay. So I will have to order a new LCD from Alibaba. The price is not bad (20€) but the estimated shipping time is 2-5 weeks! :(

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Hi Janus,

It sounds like you got a defective part from ebay. Check the connections and make sure there are no microtears, then go about removing it very carefully so that you can return it for exchange/refund. LG devices are very finicky when it comes to touch and any slight damage to the digitizer can cause them to become completely unresponsive.

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Hello, just wanted to pipe in and say I'm having exactly the same issue. I did however find a kludge if you are stuck and are willing to stay running 4.2.2. I downgraded to 4.2.2 and the digitizer now works... not a perfect solution but at least I have a phone.

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I too have had exactly the same issue. I was on Lollipop. I tried the 4.4.4 factory image but that was no good. The 4.2.2 factory image does work with this digitizer.

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I have read that Nexus 5 came with kitkat and there a no factory images 4.2.2 for nexus 5!

Can you please explain and help? :/

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TLDR: If you've downgraded to 4.2 to get a working touchscreen, try upgrading and see if it stays working.

I had a very similar experience today. I replaced my digitizer with an lcd/digitizer assembly I bought from ebay.

The touch controller chip is a "Synapdcs" [sic] 5500CB-5 with additional markings FCA6616 (I might have some of the numbers wrong, the silkscreening is very poor quality):

Block Image

Block Image

It seems to match the digitizer that Phillipe described, except with 6 chips instead of 5 (4 decoupling caps, 1 resistor, 1 diode).

My phone was running Cyanogenmod 12.1 nightly build (Android 5.1 based). When I powered it on with the new digitizer it didn't register any touches!

Disassembled and jostled connectors, reassembled, same problem. Eventually I found this thread here and also a post on the CM forums that sounds the same.

Based on the advice here I reflashed entirely back to a factory 4.2.2 image via fastboot, erasing absolutely everything, and the touchscreen worked. Yay!

(After the touchscreen came good I found out that the proximity sensor didn't work, so I had to disassemble the phone again to apply this fix.)

I didn't want to be stuck on 4.2 so I figured I'd try to fix the driver. So I installed CM 10.1.3 (Android 4.2 based), which according to the other forum post didn't work (but 10.1.2 worked). The touchscreen worked. Installed CM 10.2 (Android 4.3 based) and the touchscreen kept working.

Now I was confused. I installed the latest CM 12.1 nightly build 20150619 (ie Android 5.1 again). Touchscreen still works.

Hard power cycled the phone a few times, including unplugging from USB. Touchscreen still works. Issued a Factory Wipe/Erase User Data from Recovery mode, touchscreen still works.

So... I'm really confused!

I don't think I physically made the screen come good, although maybe I did.

The touchscreen driver includes firmware upgrade code, and it seems the firmware is stored internally on the driver chip rather than loaded from the kernel each time the phone boots. My theory is that downgrading to 4.2.2 and then upgrading through the various versions somehow created a working firmware upgrade path for the controller!

To test this theory - if anyone else downgraded to 4.2.2 to get a working touchscreen, can you try upgrading and see if it stays working? I don't know if you can upgrade directly to 5.1 or if the interim steps I went through somehow helped as well - maybe try 5.1 first and if it fails then roll back again and try step-by-step.

Finally, to help debug here's some debug output from the touchscreen kernel driver via 'adb shell'. That's under 5.1 with a working touchscreen. I didn't get output under any other versions. :(

I will make sure to post back if my touchscreen suddenly stops working again...

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For my Nexus 4, downgrading to 4.2.2 has worked (and continues to work), but any attempt to upgrade immediately results in an unresponsive touchscreen again.

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Thanks Tom. How strange that mine worked for a while.

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Hmm OK so my "Synapdics" touchscreen kept working for a few hours and then suddenly stopped working immediately after I encrypted my phone. It'd work for a brief period at boot when you unlock the disk, but it wouldn't work at all after that.

Weird!

I did a little digging in the kernel and added some extra debug output. All of the touch events from the chip have pressure value '41', every time. This leads to the kernel not outputting any ABS_MT_PRESSURE events (it only outputs events when the value changes) and I think (guess, haven't checked) that means Android is thinking there are no touches, even though the other parts of the touch event (X & Y) come through fine.

As a quick hack, turning off .is_pressure_supported in touch_caps (arch/arm/mach-msm/lge/mako/board-mako-input.c) and rebuilding the kernel seems to fix the problem, and I can use the touchscreen again.

This doesn't explain why the touchscreen worked for me previously for several hours, though. And it doesn't explain why the downgrade-upgrade cycle seemed to fix the touchscreen. And it doesn't definitively explain why the encryption unlock screen works (although maybe that screen is coded with a simpler touch algorithm that ignores pressure.)

The sysfs debug output from the "broken" Synapdics touchscreen was identical to when it was working, too.

Wil play around some more. Hopefully can isolate a "quirk" and maybe make a patch for Cyanogenmod so people with aftermarket touchscreens can run it without having to mess around.

If anyone would like to test a fixed kernel on CM12.1, please let me know (you'll need a working 'fastboot', but you can boot the kernel directly with fastboot without flashing it, so there's no danger of bricking anything.)

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Same issue. Would you please send me the patched kernel. I really want to give it a try. lshi@ku.edu Thanks a lot.

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Posted here with some instructions for testing it:

https://github.com/projectgus/android_ke...

Very keen to hear if it works for other people.

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Hi

I had or I should say have the same problem, but I found out how we can fix it, not permanently but it's better than throwing 100$ screen away plus the phone itself.

First time when I encountered with this issue I checked this topic and realized that I have to throw away my nexus phone and new screen which is my second screen that I'm replacing. But don't worry, I'm writing with my brand new screen now :D

So after you replaced the screens don't plug the digitizer's cable in, you must use the old (broken) screen digitizer's cable, plug it in and turn your phone on and waite untill the end of booting step, still the new screen is not working but now you must replace cables again, congratulations. Please remember that you should put the sim card in before turning your phone on and if you turn off your mobile you must do all the steps again. That's why I said I found a temporary way to fix it.

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I've had this problem for a few months now, my temporary solution to it is to reboot the phone into the bootloader menu and then start the phone. I'd say I have a 50% success rate with getting the touch screen to work after doing this. Could be coincidence though. ¯\_(ツ)_/¯

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Thanks, that seems to work

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Make sure if you have attached touch screen ribbon properly.

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Janus will be eternally grateful.
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