Nexus 7 BAD screen flicker!

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Nascar Dog

Senior Member
Apr 26, 2011
252
37
Calgary
Update on screen flicker

I left my Nexus 7 (16G) with WiFi disabled and in sleep mode for 7 hours but unfortunately the screen flicker is still present. :mad:

I don't know what caused my flicker to go away last night but I am unable to recreate the event.
The flicker was definitely gone until I restarted the tablet.
Too bad because the tablet is so much more usable when it is not pulsing the back-light to the tune of the WiFi signal.

I am picking up another Nexus 7 (16GB) at Best Buy today and will see if it has the problem.
 

khaytsus

Senior Member
Apr 8, 2008
7,258
1,175
Central Kentucky
I hadn't noticed this until I was in the dark reading news apps last night outside and had the backlight initially on auto. I thought the sensor detection heuristics were screwy and kept going up and down, so I turned off auto and the problem continued. I bumped up the light just a tad and the problem mostly went away but I still noticed it every so often. A little higher and it went away, but was too bright when reading black-on-white text.. This seems to be aligning with other posts, but figured I'd say "me too".

Didn't think about it last night, but tonight I'll try "Dimmer" or some other app and see if it still flickers with the backlight up highish but the "screen darker".

Dimmer makes colors darker, on AMOLED it actually lowers overall power and light output, but on regular LCD screens the backlight stays as bright as you have it set. I'm curious if it's the backlight (I suspect so) or if it's an LCD thing. Either way I doubt it's a hardware problem.

My guess: The LEDs for the backlighting need some tweaking in software. LEDs must have a constant voltage, and have to have a certain current to run, therefore they can only get a certain low output when constantly on. So to get lower effective output, LEDs are pulsed at some reasonably high frequency (40Hz, some good flashlights are up towards 140Hz) and I suspect this is what needs tweaking.
 

Nascar Dog

Senior Member
Apr 26, 2011
252
37
Calgary
My guess: The LEDs for the backlighting need some tweaking in software. LEDs must have a constant voltage, and have to have a certain current to run, therefore they can only get a certain low output when constantly on. So to get lower effective output, LEDs are pulsed at some reasonably high frequency (40Hz, some good flashlights are up towards 140Hz) and I suspect this is what needs tweaking.

So, the real question here is, How do we contact Google to let them know this is a real problem?
If we all contact them then they will at least have to look into the problem.

I found this number on http://support.google.com/nexus
855-836-3987 - Option #2

Calling now....

Update: Got an answer from Google Tech Support
OK, I talked to Google tech support and they said it is a known problem.
He said there is a fix for it and I got all excited until I heard what the fix is.
The fix is to reset your tablet to factory fresh.
I have already tried that and no change.
I even downloaded and applied the image from https://developers.google.com/android/nexus/images
and that did not help.
I unlocked it, rooted it, reset it, locked it and no change.

He then said if that does not work, the tablet needs to be replaced.
They are aware of the problem and there is a newer hardware build that fixes this problem.
He was all ready to send me a new one until I told him I was from Canada and purchased it at Staples.ca.

That tells me this is a hardware problem!!!

So, I guess the only way you are going to get this flicker problem fixed is to replace it with a newer build.

What we need to do is look at the numbers on our box labels and figure out what builds are having the problem.
 
Last edited:

tevinwade

Member
May 9, 2012
41
11
I too have problems with the screen flickering issues in low back light. The problem disappears when I turn WiFi off. I'll make a video soon.
 

qwerty123321

Senior Member
Jul 15, 2012
420
61
So, the real question here is, How do we contact Google to let them know this is a real problem?
If we all contact them then they will at least have to look into the problem.

I found this number on http://support.google.com/nexus
855-836-3987 - Option #2

Calling now....

Update: Got an answer from Google Tech Support
OK, I talked to Google tech support and they said it is a known problem.
He said there is a fix for it and I got all excited until I heard what the fix is.
The fix is to reset your tablet to factory fresh.
I have already tried that and no change.
I even downloaded and applied the image from https://developers.google.com/android/nexus/images
and that did not help.
I unlocked it, rooted it, reset it, locked it and no change.

He then said if that does not work, the tablet needs to be replaced.
They are aware of the problem and there is a newer hardware build that fixes this problem.
He was all ready to send me a new one until I told him I was from Canada and purchased it at Staples.ca.

That tells me this is a hardware problem!!!

So, I guess the only way you are going to get this flicker problem fixed is to replace it with a newer build.

What we need to do is look at the numbers on our box labels and figure out what builds are having the problem.
So I gotta retunrn this tablet for the second time and wait for a 3/red one ? This ****s ridiculous j
 

kenyee

Senior Member
Dec 11, 2008
74
4
I think the flicker seems worse initially because you're browsing the Play market and adding apps to your tablet.
All of this is related to wifi and possibly writing to SD card simultaneously. Someone on Android Central said he was able to reproduce it by using an ftp app to pull stuff onto the tablet.

Later on, it doesn't need as much wifi data access unless you stream video, but if it streams to memory, it's probably not as noticable.

FWIW, I posted on AsusUSA's facebook page and they just said get another one instead of believing it's a power circuit wifi droop issue :p

Anyways, 2 for 2 on tablets that exhibit this issue for me. Exchanging it won't make a difference IMHO...needs either a software workaround (possibly slow down wifi data transfer) or ideally extra capacitors on the backlight's power circuit to smooth out the power droop from wifi usage...
 

Nascar Dog

Senior Member
Apr 26, 2011
252
37
Calgary
Did the Google support guy say what the CSSN of the newer build is???
I'm fairly certain it's a hardware bug too...getting my 3rd one and I'll bet it flickers too :p

No, he just said there are newer builds that address this issue.
It will be up to us to figure out from the box labels what builds are faulty and which ones work.
I am going to pick another one up now and will report the info on the box label.

Would be nice if others can share the info on their box labels as well.
 

igjoe

Member
Jul 20, 2012
11
0
No, he just said there are newer builds that address this issue.
It will be up to us to figure out from the box labels what builds are faulty and which ones work.
I am going to pick another one up now and will report the info on the box label.

Would be nice if others can share the info on their box labels as well.

What box info do we need? I took a pic of mine before I returned my flickering 16gb version. I'm waiting to buy another one until I can confirm there's a way to tell it's a new non-flickering version.
 

adamhlj

Senior Member
Apr 24, 2010
632
61
Salt Lake City, UT
I don't know if this has anything to do with the issue, but in Google books there is another auto brightness feature that is selected to on by default. I turned it off and the flickering at the lowest setting in the tablet display settings seems to have gone away for me.

Sent from my Galaxy Nexus using xda premium
 

igjoe

Member
Jul 20, 2012
11
0
I don't know if this has anything to do with the issue, but in Google books there is another auto brightness feature that is selected to on by default. I turned it off and the flickering at the lowest setting in the tablet display settings seems to have gone away for me.

Sent from my Galaxy Nexus using xda premium

Is your book completely downloaded? The flickering seems to appear when data is transferring over WiFi.
 

Nascar Dog

Senior Member
Apr 26, 2011
252
37
Calgary
What box info do we need? I took a pic of mine before I returned my flickering 16gb version. I'm waiting to buy another one until I can confirm there's a way to tell it's a new non-flickering version.

Mine has a label on both ends.
One is English and the other is French

On the English one there is a Customer P/N a P/N and a Check Number.
Lets see if those are the same for all users.

On the one I just picked up at Best Buy in Canada:
Customer P/N = NEXUS7 ASUS - 1B16 - CB
P/N = AB NEXUS7 ASUS 18/T3DL/16/1G/Y
Check Number 0747

Update
So far no flicker on this new one. Doing the same things I did on the other one that flickers bad.
One difference is they changed the initial start up screens a bit. Now after entering your gmail account info it asks for a credit card before giving you the $25.00 Play Store credit.
My old one automatically applied the credit and sent me an e-mail confirming this. No credit card info required.

New Discovery
If you have a very strong WiFi signal (All bars lit up) the Nexus 7 will not flicker.
That is why the flicker went away on my Nexus 7 last night. I was sitting in a strong signal location.
When I went upstairs I had a weaker signal and that is when the flicker was noticeable again.
Today at work, I connected my newest Nexus 7 to my WiFi hotspot on my BlackBerry Bold 9900 which has a nice strong signal and that is why I thought I had a fixed one.
When I changed my WiFi to a weak network and only had 1 bar, the flicker was present.

I connected my old Nexus 7 to my BlackBerry WiFi hotspot and the flicker was gone.

So, that tells me the WiFi chip in the Nexus 7 is a cheap piece of crapolla. :mad:

Here is the new setup screen:
Setup.png


This is new, used to just give the $25.00 credit automatically, now you need to provide a Credit Card before getting the $25.00
Google%20Play%20Credit.png
 
Last edited:

Nascar Dog

Senior Member
Apr 26, 2011
252
37
Calgary
New Discovery

If you have a very strong WiFi signal (All bars lit up) the Nexus 7 will not flicker.

That is why the flicker went away on my Nexus 7 last night. I was sitting in a strong signal location.
When I went upstairs I had a weaker signal and that is when the flicker was noticeable again.
Today at work, I connected my newest Nexus 7 to my WiFi hotspot on my BlackBerry Bold 9900 which has a nice strong signal and that is why I thought I had a fixed one.
When I changed my WiFi to a weak network and only had 1 bar, the flicker was present.

I connected my old Nexus 7 (that had the flicker problem) to my BlackBerry WiFi hotspot and the flicker was gone.

So, that tells me the WiFi chip in the Nexus 7 is a cheap piece of crapolla. :mad:

Can someone with the flicker problem confirm that they do not have a strong WiFi signal when it is flickering?
 

kenyee

Senior Member
Dec 11, 2008
74
4
Can someone with the flicker problem confirm that they do not have a strong WiFi signal when it is flickering?

Yep...I reported this on the Android Central forums last week.

I think the wifi chip has to transmit stronger when there's a weak signal so it sucks more juice, which causes a droop in the backlight power circuit, then a surge as power comes back to it...the weaker the signal, the bigger the droop. That's why I think they can do a workaround that would weaken wifi performance by having it transmit at lower power or lower speed. The real fix is more caps on the power circuit for the backlight though...

p.s., and when Google was replacing tablets w/ the washed out screens, they asked for the last 3 digits of the CSSN number on the box. It's some sort of batch number....my last 4 digits are 0x101a and it still has the flicker issue...
 
Last edited:
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Nascar Dog

Senior Member
Apr 26, 2011
252
37
Calgary
Yep...I reported this on the Android Central forums last week.

I think the wifi chip has to transmit stronger when there's a weak signal so it sucks more juice, which causes a droop in the backlight power circuit, then a surge as power comes back to it...the weaker the signal, the bigger the droop. That's why I think they can do a workaround that would weaken wifi performance by having it transmit at lower power or lower speed. The real fix is more caps on the power circuit for the backlight though...

Thank-you for the confirmation that I am not loosing my mind after all this testing.
I found your post in the other forum. Funny to see the process of figuring out the problem...
http://forums.androidcentral.com/google-nexus-7-tablet-forum/190176-screen-flicker-2.html#post1989544


Thank god for the generous return policy at Best Buy.

Guess I better get a wifi extender for my upstairs. :laugh:
 
Last edited:

potentiality

Member
Jul 24, 2012
40
4
Thank you for your work NASCAR. However we still need an official response from Google. We also need the Android sites to admit this.

Steps to reproduce for ALL tablets.

1. Weak WiFi signal.
2. Backlight dimmed to under 30%.
3. A program that constantly accesses the net. Such as Google Maps.


All Nexus 7 units will experience this issue. There is no fix until a newer hardware revision is made. Again, that will take a few weeks. Screwing us over with limited RMA timeline.
 

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  • 3
    New Discovery

    If you have a very strong WiFi signal (All bars lit up) the Nexus 7 will not flicker.

    That is why the flicker went away on my Nexus 7 last night. I was sitting in a strong signal location.
    When I went upstairs I had a weaker signal and that is when the flicker was noticeable again.
    Today at work, I connected my newest Nexus 7 to my WiFi hotspot on my BlackBerry Bold 9900 which has a nice strong signal and that is why I thought I had a fixed one.
    When I changed my WiFi to a weak network and only had 1 bar, the flicker was present.

    I connected my old Nexus 7 (that had the flicker problem) to my BlackBerry WiFi hotspot and the flicker was gone.

    So, that tells me the WiFi chip in the Nexus 7 is a cheap piece of crapolla. :mad:

    Can someone with the flicker problem confirm that they do not have a strong WiFi signal when it is flickering?
    3
    It seems that on shutdown /system/bin/sensors-config will overwrite /data/lightsensor/AL3010_Config.ini. It must be pulling this data from somewhere else, like a special spot in flash memory where the factory stores the cal data. This implies that my factory calibration is borked, and it's not exactly a software problem.

    ---------- Post added at 08:08 PM ---------- Previous post was at 07:38 PM ----------

    Here's how to change the light calibration forever:

    Code:
    su
    mkdir /data/calibration
    mount -t vfat /dev/block/platform/sdhci-tegra.3/by-name/PER /data/calibration
    echo 880 > /data/calibration/lightsensor/AL3010_Config.ini
    umount /data/calibration
    rmdir /data/calibration
    3
    What box info do we need? I took a pic of mine before I returned my flickering 16gb version. I'm waiting to buy another one until I can confirm there's a way to tell it's a new non-flickering version.

    Mine has a label on both ends.
    One is English and the other is French

    On the English one there is a Customer P/N a P/N and a Check Number.
    Lets see if those are the same for all users.

    On the one I just picked up at Best Buy in Canada:
    Customer P/N = NEXUS7 ASUS - 1B16 - CB
    P/N = AB NEXUS7 ASUS 18/T3DL/16/1G/Y
    Check Number 0747

    Update
    So far no flicker on this new one. Doing the same things I did on the other one that flickers bad.
    One difference is they changed the initial start up screens a bit. Now after entering your gmail account info it asks for a credit card before giving you the $25.00 Play Store credit.
    My old one automatically applied the credit and sent me an e-mail confirming this. No credit card info required.

    New Discovery
    If you have a very strong WiFi signal (All bars lit up) the Nexus 7 will not flicker.
    That is why the flicker went away on my Nexus 7 last night. I was sitting in a strong signal location.
    When I went upstairs I had a weaker signal and that is when the flicker was noticeable again.
    Today at work, I connected my newest Nexus 7 to my WiFi hotspot on my BlackBerry Bold 9900 which has a nice strong signal and that is why I thought I had a fixed one.
    When I changed my WiFi to a weak network and only had 1 bar, the flicker was present.

    I connected my old Nexus 7 to my BlackBerry WiFi hotspot and the flicker was gone.

    So, that tells me the WiFi chip in the Nexus 7 is a cheap piece of crapolla. :mad:

    Here is the new setup screen:
    Setup.png


    This is new, used to just give the $25.00 credit automatically, now you need to provide a Credit Card before getting the $25.00
    Google%20Play%20Credit.png
    2
    Thank you for your work NASCAR. However we still need an official response from Google. We also need the Android sites to admit this.

    Steps to reproduce for ALL tablets.

    1. Weak WiFi signal.
    2. Backlight dimmed to under 30%.
    3. A program that constantly accesses the net. Such as Google Maps.


    All Nexus 7 units will experience this issue. There is no fix until a newer hardware revision is made. Again, that will take a few weeks. Screwing us over with limited RMA timeline.
    2
    My xperia x8, x10 mini, x10 mini pro, xperia arc had the same problems initially. They all were fixed every after software update.

    Even Cyanogenmod has settings tweak to reduce flickering when set in low brightness.

    I really believe it is caused by software. Backlighting LEDs are controlled by software via pwm. The pwm may be conking out and not producing enough voltage when there is high current draw from the wifi. But it don't do that when watching videos where the most current draw should be taking place. Probably because of the Tegra 3 energy-saving feature when watching videos, but I really can't tell. I am pretty sure they'll come up with a fix either set hysteresis not to adjust logarithmically, reduce wifi tx/rx power maybe, adjust voltage to pwm, etc. There are many ways to skin the cat so to speak.

    Sent from my Nexus 7 using xda app-developers app