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My monitor displaying 1 inch blurry vertical lines across screen


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#1 jag123

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Posted 26 October 2015 - 10:54 PM

Hello,

I have an HP ProBook 4520s laptop that has a lcd that doesn't work so I had to connect it to an

external monitor. Now the external monitor is showing 1 inch blurry vertical lines going across the screen. See attached screenshot.

 

The external monitor works fine with another pc.

Any idea what's causing this and a solution?

Thank you.

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#2 CodeSmasha

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Posted 26 October 2015 - 11:12 PM

The lines are caused by the traces going bad in the video cable going from the screen to the main board. Generally they wear out over time from opening and closing the lid, because the cables tend to flex.



#3 jag123

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Posted 26 October 2015 - 11:48 PM

But since I'm using an external monitor with a vga cable wouldn't the faulty laptop cable to the laptops monitor not be a factor?

#4 Platypus

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Posted 27 October 2015 - 02:47 AM

The external monitor works fine with another pc.


On VGA using the same cable?

Does your particular ProBook model use the Intel video or does it have the ATI video option?
 
There are a number of things you can try to help diagnose the probable location of the problem:
 
Is there any way you can arrange to try the HDMI output instead?
 
Change to a different resolution, and tell us how the lines change.
 
Take a screenshot instead of a photo. On VGA, if the lines aren't in the screenshot, the video chip probably has a faulty DAC, and they also should not appear on HDMI. If they show in the screenshot, it would be a video chip or memory fault, and would probably also show on HDMI, although you might be lucky and have it not appear.
 
If the unit has more than one DIMM and is using Intel video, you can swap their position and see if it is a memory fault, since the Intel will be using system RAM as video memory.

Edited by Platypus, 27 October 2015 - 02:51 AM.

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#5 jag123

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Posted 27 October 2015 - 11:16 AM

Thank you platypus for your in-depth reply!

To answer your questions:

Yes I tested the monitor on a different pc with the same cable and it was fine.

My HP ProBook has the ATI video option.

I tried using the HDMI connection but when I switch to the hdmi input the screen turns black and it says no signal and then after a bit goes back to the vga connection with the blurry lines.

Yes I tried different resolutions and refresh rates but that didn't work as the lines were still appearing.

However I did take a screenshot and the lines did not show up in it. You said that it might be a faulty DAC? What exactly is that and is it fixable? I'm comfortable opening the laptop up if needed.

Thanks again.

Edited by jag123, 27 October 2015 - 11:17 AM.


#6 Platypus

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Posted 27 October 2015 - 06:27 PM

That's not looking good at all - the signs point to faulty video, which is normally integrated into the mainboard in a laptop/netbook, or at least partially provided by the CPU in a hybrid configuration. What CPU is in yours? What was the nature of the original LCD screen failure, damage to the screen, or did the video signal stop working?

The DAC (Digital to Analog Converter) is part of the video chip and can't be attended to in any way on its own. It changes the digital image data used by the video chip and displayed by the LCD screen and HDMI, into an analog signal to drive a VGA screen. If the lines are not seen on a screenshot, the image is OK in the screen buffer in the video chip, but going bad after that. If only the VGA had a problem, it might be the DAC stage, but since the HDMI also doesn't want to work, the video chip is probably faulty, or has broken solder connections where it is attached to the board.

This normally requires a mainboard replacement, or a professional board repair, both expensive options.
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#7 jag123

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Posted 27 October 2015 - 09:10 PM

It's an Intel i5 core processor. ATI Mobility Radeon

I'm not sure what's wrong with the lcd on the laptop. It basically just stopped working (blank black screen). So I just have had it connected to the external monitor for now.

I know sometimes the lcd cable goes bad from opening and closing the case or maybe it's the lcd panel itself. But if you're saying it's a motherboard problem then I'm guessing fixing the cable or replacing the lcd wouldn't matter.

#8 Platypus

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Posted 27 October 2015 - 10:24 PM

Black screen can be a backlight fault. If it is, when you cycle the screen so it should be showing on the netbook LCD, if you darken the room and hold a torch gently against the front of the screen, you should be able to faintly see the desktop image by the ring of reflected light around the torch. If not, then it would further support video chip failure.

Using the reverse diagnostic process, when the netbook screen should be showing, if you are in a dark room and the backlight is operating but the LCD is getting a black image, you should be able to see a faint backlight bleed showing through.

Is a specific adapter shown as driving the VGA screen in the video properties, e.g. VGA monitor on Intel HD graphics, or VGA monitor on Radeon HD 5470?
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#9 jag123

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Posted 27 October 2015 - 11:37 PM

I tried your suggestions above using a torch but I couldn't see any traces of a Desktop image.

However after checking my system status in control panel I saw a message stating the ATI graphics cards are not working.

Under device manager > display adapters

Standard VGA Graphics Adapter

Below is the latest performance info:

System
Manufacturer Hewlett-Packard
Model HP ProBook 4520s
Total amount of system memory 8.00 GB RAM
System type 64-bit operating system
Number of processor cores 2
Storage
Total size of hard disk(s) 450 GB
Disk partition (C:) 208 GB Free (448 GB Total)
Disk partition (F:) 1 GB Free (2 GB Total)
Media drive (G:) CD/DVD
Graphics
Total available graphics memory Not detected
Dedicated graphics memory 0 MB
Dedicated system memory 0 MB
Shared system memory 0 MB
Display adapter driver version 6.1.7600.16385
Primary monitor resolution 1280x1024
DirectX version DirectX 8 or earlier
Network
Network Adapter Ralink RT3090 802.11b/g/n WiFi adapter

#10 Platypus

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Posted 28 October 2015 - 02:31 AM

No evidence of an image on the built-in screen, ATI graphics reported not working and no detection of video memory are all symptoms that could be expected if the video chip was faulty. But for a VGA screen to operate, some video memory must be being used, and something is generating the graphics.

Does the BIOS setup screen display on the VGA monitor? If so, does it have stripes, and is there an option to select video between Intel/ATI/hybrid?

Edited by Platypus, 28 October 2015 - 02:33 AM.

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#11 jag123

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Posted 28 October 2015 - 11:56 AM

Yes as soon as I turn the laptop on and monitor comes on I see the stripes.

I can get into the Advanced boot options for Windows 7 but it's difficult to read them because of the stripes.




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