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lcd monitor showing horizontal shaked image but osd ok

Discussion in 'Troubleshooting and Repair' started by myke, Feb 4, 2010.

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  1. myke

    myke

    3
    0
    Feb 4, 2010
    Hello,

    I have a problem with a LCD monitor, i will describe it below.

    The monitor displays the image from pc (VGA) but it shakes it horizontally. There are horizontal lines all over the image that move left-right for approx. 1-2 centimeters, vizible at the side. Basically, the entire image is moving left and right line by line simultanously.

    The monitor itself is a Samsung SyncMaster 720N, 17 inch, 3 years old.

    The most interesting fact is that the OSD of the monitor is displayed correctly, without any distorsion. So only the image that comes from pc is displayed wrong.

    Now, regarding the tests i've made:
    - i've tested on 2 latops and 2 desktop computers
    - i've tested using 2 different VGA cables
    - i've tested using different resolutions and refresh rates (from 800x600 to 1280x1024 and from 60Hz to 100Hz). the effect is the same, only on 100Hz refresh rate the horizontal shake of the image is much more strong, the lines move faster and longer.
    - i've tested with different power lines and outlets, one in my house, other in a friend house (i've read some forums where they've suggested that).
    - the autosetup function of the monitor doesn't change anything
    - i've opened the monitor, i've checked the capacitors and the other components, they do not present any visual sign of malfunction (like leeky capacitors or exploded), some say that an electrolitic capacitor may be dead, but i dunno how to test for it (all i got is a MAVO)
    - i've measured the voltage on the power supply board, there are 2 wires for +5V, one for +2V, ground and sleep, all measure ok.
    - the chip from the logical board is tsum16al-lf. i've googled it but found nothing other than it's made in China and costs approx 40 euros (which basically, if this is the damaged component, would make the replacement unpractical, the cost of the chip is almost a third from the price of a new monitor)

    I am curios to know what can be the problem, especially because the OSD is displayed correctly. So maybe somenthing in the analogue-digital convertor? (from VGA to digital).
    I am more interested in knowing the cause of this malfunction for pedagogical reasons.

    myke.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,251
    2,704
    Jan 21, 2010
    All of your attempts to isolate the problem seem sensible, and would certainly indicate the problem lies with the monitor.

    I had a similar problem with a monitor some time ago. It's colour had gone way off. It looked like it was set for a colour temperature of about 1000K or that the backlight was red.

    However, as in your case, the OSD was perfect, showing up in the bright and clean colours I expected.

    It was sent back under warranty and the fix was that an eeprom was reprogrammed.

    In my case it was a software fault that had caused an issue which looked *exactly* like a hardware fault.

    In your case too, the OSD is perfect...

    It is certainly possible that the fault is in the analog circuitry, but the problem appears to be more about the timing of the start of each scan line. If you could isolate how the start of each scan line is signalled, that may be a place to start.

    Oh, if you can check the clock used by the processor in the monitor. If that has become very unstable, it might also cause problems (although I'd expect it to change more than just the start of each scan line)
     
    Last edited: Feb 4, 2010
  3. myke

    myke

    3
    0
    Feb 4, 2010
    Hello, thank you for replying me.
    It is really interesting what you are saying about the problem you had and if that is the case on my monitor too, then there's pretty not much to do.
    I don't have the equipment, nor the datasheet for the processor inside the lcd to isolate how each line is signaled.
    I have a frequencemeter though and i've checked the clock, it is at 22MHz and it goes down to 21,9MHz from time to time (at intervals of about 30s).
    I've replaced some capacitors in the psu unit, i was adviced by a moderator from another forum, but still nothing.
    Anyway, I'm affraid that's pretty much it, since i don't have all the equipment i would need to make all the neccessary tests.
    Thank you for your help, if you have any other ideas i'm open to listen them.
    Myke.
     
  4. myke

    myke

    3
    0
    Feb 4, 2010
    this is how the image looks

    I wanted to post a photo taken of the monitor in cause, just so you can see how the image looks like (remember that the osd is fine if showed, no distorsion), just in case smb else will have a similar problem to find this thread.
    myke.
     

    Attached Files:

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,251
    2,704
    Jan 21, 2010
    You know, on the basis that a man carrying a hammer will see every problem as a nail, I would be inclined to have a look at the power supply and check the capacitors for signs of swelling.

    If you look for faults in LCD monitors it seems a huge proportion of them are related to bad capacitors.

    I could envisage that the additional ripple (at the power supply switching frequency) could interfere with the timing the monitor does to know when a scan line starts. I'd assume this is done digitally, but if it still relies on a ramped voltage, the ripple could interfere with this.

    If you don't want to go removing and replacing all the caps, you could temporarily add some additional filter capacitors to the PSU output and see if it makes a difference.

    Edit: I actually came across this while trying to figure out how to open my monitor. The problem this guy has seems very similar to yours. And his OSD is also perfectly formed. This suggests to me that the fault is not something really weird and bizzare. At least you're not alone :)
     
    Last edited: Feb 6, 2010
  6. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    I second steve. Sync circuits are often voltage sensitive and so can make horizontal shifts to the picture when there's ripple on the supply.
     
  7. jerryg50

    jerryg50

    57
    0
    Apr 18, 2010

    The fault is most likely in the input processor board. The input processing is not having steady clocking. Without the proper scope and knowing the proper test points you will not be able to see this in the circuit.

    A fair number of times I found the decoupling and coupling capacitors on this board to have high ESR from age and heat. After changing the caps the problem was fixed. You should use an ESR meter to test the capacitors. These should be the metal colored surface mount electrolytic caps on the board. Some of the older series used standard looking electrolytic caps.

    Also, it is important to make sure the caps in the power supply are not high in ESR. The power supply caps if not in spec can cause noise transfer through the power distribution to the various areas of the monitor.


    Jerry G. :)
     
    Last edited: Apr 21, 2010
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