Recently, I built my first computer:

After confirming the computer boots/POSTs fine, I attempted to install Windows 8 Dev Preview, x64 via USB, and it was extremely slow (i.e. taking many, many hours to install). I tried a number of things, eventually taking out all but 1 stick of RAM, and Windows Setup proceeded much faster - however, when Windows went to logon, the screen starts to fuzz/zig zag*, it only happens when the resolution is above 800 x 600 resolution; the monitor is set to use 1024 x 768 pixels. I first used the drivers from the CD, then went and downloaded AMD's latest drivers specifically for Windows 8. Nothing helped, not even uninstalling completely and then reinstalling the drivers.

Next, I decide to install Windows 7 Home Premium on a different partition. Same scenario with the RAM, had to take out all but one stick. Installed quickly with no issues, I even booted into Windows with no fuzzing/zig zagging issues, but couldn't use Aero, since there were no drivers installed for the graphics card - so I downloaded the latest drivers for Windows 7 x64 and rebooted, and got the exact same problem, the fuzzing/zig zagging.

I've tried all kinds of things, from installing all the latest updates in Windows (including SP1), unplugging different devices (such as the IDE DVD/CD drive), double-checking the GPU PSU connection, etc.

My question: Why is this happening at resolutions higher than 800 x 600 and what can I do about it?

*By fuzzing/zig zagging, I mean this, but vertical, and you can still see the image the entire time, it just blurs/fuzzes quickly, and then clears, and then fuzzes again.

Update (12-29): I swapped out my Corsair 400w PSU for a Corsair 650w, and when I boot Windows 7, the fuzzing/zig zagging is still present.I'm suspicious of my DisplayPort -> VGA adapter, should I try a DVI -> VGA?

Message received from XFX Support:

Why are you using Displayport to VGA adapters? A DVI to VGA adapter is much more natural since it isn`t really adapting anything. I think that the fuzziness is being cause by the adapter that you are using. Most 6770s ship with one DVI to VGA adapter. The power supply that you are using is fine for this card and that computer. Thank you.

Is this true, that a DVI -> VGA is more natural? Should I try a DVI -> VGA next?

  • 2
    Running Windows Memory Diagnostics Tool now. – studiohack Dec 23 '11 at 18:15
  • +1 For once a troubleshooting question that shows the user didn't come here unprepared. – Daniel Beck Dec 23 '11 at 18:50
  • So it looks like "video transmission" in computer games and movies, with intermittent artifacts? The link is only the pattern of how the pixels are moved around? Have you tried a Linux live CD with resolution >800x600? – Daniel Beck Dec 23 '11 at 18:53
  • If available, try a new power supply, and then a new graphics card. – Ƭᴇcʜιᴇ007 Dec 23 '11 at 18:58

The type of noise you're getting is consistent with analog noise. Analog noise can be introduced from poor grounding, poor wires, and poorly grounded wiring, poor connections, or a *Ground loop***1**. Ground loops can often be resolved by getting AC wall power from the same place at the same distance.

The noise could be coming from any interference from another device that gets induced into the wiring, or circuitry areas. There is a lower possibility that the noise could be generated at the chip itself making the analog signal, when it is under-powered, or getting noisy or dirty power, or just from generally poorly done electronics.

Changing the "adaption" might help. With DVI-to-VGA simple adaption, Digital DVI is not "converted" to VGA analog. Generally there is an analog signal THERE in the video card, at the DVI connection port. DVI-to-VGA simple adaption will not even work if the video card itself did not have the analog signal available at the DVI port.

The DVI to VGA (simple) adapter connects the VGA output that exists on the card. It is possible to do a DVI-to-VGA analog conversion, but it's usually unnecessary, and doesn't exist with cheap simple adaption.

On some Dual DVI ATI card, VGA is available on only one of the ports. The primary port had the VGA on my card.

DVI port designations: DVI-I stands for DVI-Integrated and supports both digital and analog , so it works with both digital (DVI) and analog (VGA). DVI-D stands for DVI-Digital and supports digital transfers only.

An "active" adapter, or one that needs powering, or has circuits, is often a "converter", not just a connection. A good conversion from digital to analog can be very expencive $$$. A bad conversion will make analog look much worse than it is, with noise, fuzzy picture and bad interpolations. . A cheap analog-to-digital conversion will look worse at higher resolutions, and sometimes not even do higher resolutions. Bad conversions lead people to believe that analog is worse than it actually is.

If the display port does not have a built-in analog output, and it is being converted from a digital signal then it is going to look like it was processed with a 12$ chip in the cheap converters. The analog signal that is available (via the DVI port) on cards like the ATI $$$ cards is usually much better designed and protected than any $30 adaption methods.


1 Ground loops are not really ground loops! They are power differentials between two devices that end up passing power between the two devices in a incorrect way. They were probably originally named "ground loop" because proper grounding of everything solved the problem.

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Bigger power supply. Minimum of 500W is recommended by the manufacturer. Although power supply calculators say it will work with lower units, I have found by experience that you get better results going to at least the minimum. When planning out systems for my customers, I usually go 10-15% higher then their minimum requirements

Usually that fixes it... But Psycogeek has the right idea: With DVI to VGA, it doesn't convert the signal. It simply re-routes the pins into a VGA form

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  • Luke: I've accepted @Psychogeek's answer, as this has fixed the problem. +1 to you as well. Cheers! :) – studiohack Jan 13 '12 at 20:35

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