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Screen flicker issue

Last response: in Graphics & Displays
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April 9, 2010 2:29:15 PM

Hi,

Let me start with some background information;

This is a pc built into a public kiosk. The pc is on a motherboard tray that is mounted inside the kiosk without a case. Could this be an issue? Interference from electronics or electrical wiring? The screen is also opened at the back with wiring on show, as that is how it fits the kiosk.

The graphics card is Sparkle Nvidia Geforce 9800GT Low Profile. It's connected to the screen via a shielded VGA cable with a DVI to VGA adapter on the card. The screen only has VGA and DVI ins.

The PC OS is Windows XP.

Now, here is the issue;

The screen has a constant flciker/wave/wobble going on it the background. Kind of like what you would see on screens when you filmed a screen and then watched back the footage of the screen.

I have done some research and at first thought it might be a 'ground loop'. They say this is caused when you have the screen and pc plugged into the same plug board with both plugs being earthed. Also, the screen and pc hooked up via VGA cable. It creates an interference loop that causes the screen to flicker/be wavey.

But I tried a new plug without an earth for the pc and it was still there. Also tried the non-earted plug for he monitor, still no joy. So I'm ruling that one out.

I have also read a thread on here about a similar problem for ATI cards, but as it suggests in that thread, I won't try the fix in that thread for an Nvidia card, without asking here first. The problem in that thread was the card being overclocked and needed to have the frequency cut back. Could that be what's happening here too?

Other things I have tried;

Hooking screen to pc directly with DVI cable. Nothing will come onto the screen whatsoever when I do this. Just says no VGA plugged in and goes black. Do you have to activate DVI on the card or Windows? I thought it would just auto switch once the cable is in.

I also tried upping refresh rate to 75 and also upping the resolution. This helped a small bit but there was still waves.

Does anybody have a clue what could be causing this? How I could fix it?

Cheers.

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a c 1410 U Graphics card
April 9, 2010 9:48:04 PM

Ground the motherboard tray to the PSU. (they are grounded together through the case in normal cases). On the DVI issue you might have to change input mode on your monitor, see if you have a mode selection in menu.
April 10, 2010 11:54:52 AM

Thanks for the suggestion rolli.

How best would you recommend me to ground the motherboard tray with the PSU? They are seperated by about two inches.
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