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c3141rog
08-09-2013, 05:01 PM
I've been doing some digging on the screen issues and I think I know what is causing the issue. Unfortunately, it is not something that is readily fixable.

An LCD is made up of fixed grids of pixels. Each pixel on a color LCD has three subpixels, one for red, one for green, and one for blue. Each subpixel contains a liquid crystal plus a filter for whatever color of light that subpixel is. Liquid crystals are unique in that they are normally transparent but can be made opaque (to block light) by applying an electrical voltage to them. By manipulating these liquid crystals, one can control what parts of the screen the backlight shines through in order to form an image.

When an LCD is manufactured, it has to be calibrated. Variations in the manufacturing process mean that different LCDs have different voltage requirements. The idea of LCD calibration is to get consistency between manufactured panels so that a brightness value of, say, 10, is always the same amount of brightness no matter the panel. Voltage calibration involves mapping the brightness values of each subpixel to the voltage that will let enough light through to get the appropriate brightness.

Sustained electrical current will polarize the liquid crystals and damage them. In order to avoid this, LCDs invert the voltage of the liquid crystals, switching from positive to negative (and vice versa). The inversion rate is typically about half of the refresh rate so for a 60hz screen, the sub-pixels will invert at 30hz. In an ideal situation, the positive and the negative voltage would be exactly the same (i.e. +2.543v and -2.543v). Unfortunately, current technology means that the positive and negative voltages are not going to line up 100% so you might instead get +2.543v and -2.520v. This means that when the subpixels are inverted, the brightness changes. The above calibration process also involves trying to get the positive and negative voltages as close together as possible.

Most LCDs will also mitigate inversion related flicker by using something called an inversion pattern; instead of making all of the subpixels on the screen the same polarity, they typically invert in such a way that one row is positive and the next row is negative and so on. The idea is that the two brightness levels will average themselves out so that the user does not get flicker from the polarity inversions. Inversion patterning, however, is dependent on proper calibration because no pattern will help if the brightness differences between positive and negative polarity are sufficiently large.

Both the horizontal lines issue and the flickering issues that people have been having are symptoms of improper calibration. At first, I thought it was a dithering problem but I took a look at the screen under a microscope.

For me, it appears on my laptop that the calibration of the green subpixels is off. The horizontal lines, when looked at under a microscope, alternate between rows. This means that one of the polarities has a voltage scale that is too high. (Remember that voltage causes the liquid crystals to block light). At very low green levels, the voltage becomes high enough to block light and produce a black color. Because only one polarity is off, the lines that are one polarity will be green and the other will be black. This is what produces the horizontal lines. In addition, this is why flicker is so noticeable. It also explains why some people are more affected than others; some panels may not be as miscalibrated as others.

Unfortunately, there is no easy way to adjust the voltages because big LCD screens use digitally controlled potentiometers. You would most likely need to desolder the EEPROM on the LCD control board and use a chip programmer to access it. In addition, you would also need to know where the settings for the voltage are kept and the format of that data. It may be possible to use driver tricks to work around this issue; you could, for example, clamp green values at certain levels. If the driver had a way of synchronizing with the inversion of the screen, it could also boost the brightness on the miscalibrated polarity to compensate for voltage differences.

TekNiko
08-09-2013, 06:17 PM
I'd like to contribute what I've got so far on this issue as well. It seems that the "Chi Mei 173HGE" display has been used on several other laptops as well and users have complained about it. Dell even issued an official statement about it and stopped using these displays completely on their Precision m6600 notebook. They offered a free swap to an LG or AUO type of display.
http://forum.notebookreview.com/dell-latitude-vostro-precision/580712-m6600-owners-thread-150.html

So that's that. We have a crappy display. I just had an interesting chat with Asus support though. This might help others who are also experiencing this issue to make a decision regarding their own laptops. Below is the transcript of our discussion:



Sheldon
Hello TekNiko, thank you for contacting ASUS support. At the end of this chat please take the time to fill out a brief survey and rate the overall experience at the top of the chat window. How can I help you today?

TekNiko
Hi Sheldon. I will keep this very simple. I only have a few questions. Please answer this one first: Do all Asus G750JX laptops sold in Singapore use "Chi Mei 173HGE" as the laptop display?

Sheldon
I would be glad to help you.

I am sorry , unfortunately I am unable to confirmed if all models G70JX sold in Singapore use "Chi Mei 173HGE" as the laptop display, however this can be confirmed with the Resellers before purchasing

I sincerely apologized for the disappointment

TekNiko
OK. Let's assume that all of them are "Chi Mei 173HGE". Can I have the Asus Service Center upgrade the laptop display to a different type of screen? I am willing to pay extra for an upgrade if required.

Sheldon
I understand, however I am seeing where this display is optional. Unfortunately Asus doesn't provide support for upgrades although you are paying so I will recommend to contact a certified Technician if you wish to have this done.

TekNiko
OK. I know it is definitely possible to swap to a different type of display, for example a FHD 3D 120Mhz display instead of the matte finish Chi Mei display. If I go to a certified Asus Technician to have this done, how will it affect my warranty? Will my warranty still be valid for all the other parts aside from the display?

Sheldon
Let me check on this for you, please hold

TekNiko
Sure. Thank you

Sheldon
Thank you for your patience.

Unfortunately replacing your may voids your warranty, however if the warranty seal is not broken it may still be serviced under warranty and when sending in for servicing we will suggest you sent back the Notebook with the original screen it came with

TekNiko
I would understand that by replacing the display, the new display would of course not be covered under the out of the box warranty. However, are you saying that all of the other parts of my laptop would be void of warranty as well if the display is replaced? Where is this warranty seal located? Will the warranty seal need to be broken in the process of replacing the LCD?

Sheldon
No, I am not saying all your other parts warranty will be voided. However if you are sending your Notebook for servicing you could send it back with the original screen it came with

There is not a specific spot where the warranty seal is located

However the warranty seals are normally located near the RAMS etc

TekNiko
But what if the warranty seal happens to be broken during the process of upgrading/replacing the display? Will that void the entire warranty on all parts?

Sheldon
If the warranty seal is broken your Notebook warranty will be voided automatically, I sincerely apologize for the disappointment.

TekNiko
You have been very helpful Sheldon. That answers all my questions. Here's to hoping the warranty seal on my unit is in a safe place. Cheers :)

EpIcSnIpErZ23
08-10-2013, 12:26 AM
I think my G750JW has a Chi mei display also. I haven't noticed many lines, but i get the occasional few. Why won't they upgrade for free? It is their issue. Not ours.

TekNiko
08-10-2013, 06:18 AM
I just got back from the Asus service centre here in Singapore. They took my laptop in and are going to replace the display. The tech seemed understanding and acknowledged the horizontal lines. I explained that many others are experiencing the same issue specifically with the Chi Mei 173HGE screen. The tech said they will need to consult HQ to determine the appropriate course of action regarding the display, but most likely they will replace it with a different kind of display other than Chi Mei. In the case that they don't have any other type of display for the G750JX except the crappy Chi Mei LCDs, they said that they will make sure the replacement display will not exhibit the horizontal lines issue.

For others out there dealing with this issue, a piece of advice is to contact Asus directly. Don't waste your time asking for help or replacements from resellers like Best Buy or in case you're in Singapore, Challenger.

So far the Asus support team has shown some good customer service. I hope they can follow through and deliver.

YesNoYes-
08-18-2013, 07:39 AM
I just got back from the Asus service centre here in Singapore. They took my laptop in and are going to replace the display. The tech seemed understanding and acknowledged the horizontal lines. I explained that many others are experiencing the same issue specifically with the Chi Mei 173HGE screen. The tech said they will need to consult HQ to determine the appropriate course of action regarding the display, but most likely they will replace it with a different kind of display other than Chi Mei. In the case that they don't have any other type of display for the G750JX except the crappy Chi Mei LCDs, they said that they will make sure the replacement display will not exhibit the horizontal lines issue.

For others out there dealing with this issue, a piece of advice is to contact Asus directly. Don't waste your time asking for help or replacements from resellers like Best Buy or in case you're in Singapore, Challenger.

So far the Asus support team has shown some good customer service. I hope they can follow through and deliver.

Can you update us if the laptop was returned to you with the screen now setup right with no line/flickering or maybe they changed the display type all together?

TekNiko
08-20-2013, 05:33 AM
They changed my Chi Mei panel to an AUO v1 panel. It doesn't have horizontal lines anymore but now it has vertical lines. The vertical lines are slightly less visible than the horizontal ones. I'm choosing to save myself the headache and replace the LCD myself. Even with the additional cost of replacing the LCD, the power/performance ratio is still better than other laptops in the same category.

c3141rog was able to swap his display with a glossy screen. I plan to do the same
http://www.hidevolution.com/auo-au-optronics-b173hw01-v4-17-3-fhd-led-display.html

TekNiko
08-22-2013, 03:19 PM
Update on the issue:

I updated my nvidia drivers to 326.80 and the lines are gone. hooray!

Pierre990429
09-09-2013, 06:21 AM
Hi TekNiko, this is my first post here.

I'm from France and got a G750JH with Geforce 780M. My screen is an AUO panel (B173HW02 v1). Like you, I can see faint vertical lines. I thought it might be the antiglare coating or the way the panel is built.
Do you confirm that upgrading the drivers (from 311.83) resolved the issue for you ?
If so, how do I have to proceed ? Do I have to mod the drivers ?
I think some users described weird behavior after installing 326.80 (like a black screen on log-on and the necessity to reboot 4 / 5 times to fix this ? ) ?
Do these drivers still work for you?

I was already thinking about changing the screen myself, for a glossy one.

I have read somewhere that Asus France won't do G750JH's with 3D (glossy) screens.

I have the G750JH-T4076H ; in France you can also get the G750JH-T4040H.

http://www.asus.com/fr/Notebooks_Ultrabooks/ASUS_ROG_G750JH/#specifications

Cheers from France,

Pierre

patros
09-09-2013, 09:17 AM
I've been reading this thread and noticed one thing. Asus seems to have a wide variety of screen OEMs supplying their G750s. That being said, it seems the West is getting the AUOs and the CHI MEIs etc., while here in India my display is a Samsung on my G750JX. Is it that only the matte displays are these nondescript suppliers while the glossy 3D screen is by Samsung or is there a different in parts being used depending on the big retail store / price point / market?

Flea0
09-09-2013, 10:24 AM
I think I remember finding that my 3D screen is a Samsung as well, and I bought mine in Italy.

patros
09-09-2013, 10:30 AM
Looks like the matte screen option on the Asus G750 then ain't worth it, period.

A lot of people justify their preference for the matte screen citing a variety of reasons I find rather here and there and not really valid.

It appears that if you want to buy an Asus G750, you're best buying the one with the 120 hz 3D display instead of the matte version. It may cost a bit more, but you get what you pay for in the end.

If I were to open a thread citing hardware specifications of each model so users can share what hardware configurations come under the Asus G750 banner, would it be worth it? Maybe, therefore I am doing that right now.

Flea0
09-09-2013, 11:51 AM
by the way, yesterday I discovered that the screen had reverted back to 60Hz mode, so I had to manually set it back to 120. I'm guessing some videogame is responsible, but how can I make 120Hz the default refresh rate for the screen?

patros
09-09-2013, 12:13 PM
I just noticed that myself and manually changed it back to 120 hz. Any ideas guys?