lcd monitor showing horizontal shaked image but osd ok

[myke]

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.

 

[Nigel Goodwin]

Most likely cause is electrolytic capacitors having gone high-ESR - particularly common with Samsung, as they use cheap crap capacitors. You need an ESR meter to test them, or use a scope to measure the ripple on them with the set running.

 

[myke]

Hi, thank you for answering me. If it is an electrolytic capacitor who broke it's good, cause that's easy to fix. Unfortunatelly i don't have either an oscilloscope or an ESR meter at home. Tell me please, in which part of the monitor a damaged capacitor is most likely to cause this effect? The monitor has two PCBs, one for the power supply and one for the logical unit. The power supply has some medium to large electrolytic capacitors and the logical part has some smaller ones. If you could tell me where the damaged one is most likely to be, i could try to see if I have replacement capacitors and try to change them all (they are only a few).

 

[Nigel Goodwin]

In the PSU, usually in the secondary side.

It's essential to use 105 degree capacitors, and preferably low-ESR ones.

 

[myke]

Hello, thank you for coming back at me,
I've replaced some capacitors on the psu unit but the result is still the same.
I've checked the clock on the logical unit too (at the advice of a member from another forum) and it's at 22MHz and pretty stable.
Anyway, i gues this is it, since i don't have other testing equipment. If you have any other ideas i'm open to listen them, probably though it's the chip that's damaged somehow.
myke.

 

[myke]

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.

 

[mneary]

Try a new VGA cable. The shield/ground/earth line might be open.

 

[myke]

Thank you for your suggestion but i've already done that and the result was the same. Do you think it could be some sort of shiled malfunction inside the monitor itself? there are no coaxial cables or something like this inside, but clearly the problem is inside the monitor (and as I was adviced, only a specialized repair shop would be able to establish the cause of this).
myke.