Laptop/VGA/DVI-D connection

June 3, 2006 7:55 PM

So I got a new LCD monitor as a second display for my VGA-outputting laptop, but I want to use the DVI-D in on the monitor, because the analog VGA-in flickers. Technical details inside.

I have an HP ZD7000 laptop with a VGA output to connect an external display. I do a lot of design work and needed a very large second screen for palettes, etc., so I got a 21" widescreen LCD, the Samsung 215TW.

When I connect the VGA out from the laptop to the VGA in on the LCD, I get a really annoying constant and random flicker on the LCD, particularly when there is nothing being displayed and the screen is black. I've taken to keeping my e-mail open on the second screen just so I'm not distracted by the flicker, but even that is distracting in a different way because it's so bright all the time.

The laptop runs at a native res of 1440x900 and the LCD's native res is 1680x1050. The video card in the laptop is an NVidia GoForce FX Go5600 with 128MB of RAM. Both the video card and display are set at the default 60hz, so I don't think that's the issue.

But even though the laptop can drive the displays at those resolutions, I can only guess that it just doesn't have enough juice to send a solid enough analog signal to the large LCD (the connection is fairly short, otherwise, so I don't think it's picking up interference along the way (I tried attaching some ferrite cores to the VGA cable with no effect.)

(feel free to offer alternative suggestions to this problem, as it's the fundamental issue at hand).

So, because the LCD also supports a DVI digital connection, I wanted to try using that, since perhaps a digital connection will not suffer from the same flicker as the analog -- digital should either be there or not, right? No flicker?

Therein lies the problem. I can find any number of cheap (< $10> VGA->DVI adapters. But, in my research I learned that there are actually several flavors of DVI (thanks, IEEE) and the particular flavor on the back of the Samsung is DVI-D Dual Link.

Of course, there are no cheap adapters for that, I imagine because it's not possible to just magically change an analog signal to digital with a $7 adapter.

I'm guessing at this point that I would need a ~$300-$400 VGA/DVI signal converter to use the DVI input on my LCD, which is of course not feasible since that's almost the cost of the monitor itself. Even if I did decide that it was worth it, I'd be buying it under the assumption that a digital connector would even solve the flicker in the first place, and likely have to return it (to an online retailer, no less) if it doesn't.

Is that the boat I'm stuck in?

I really like the resolution and form factor of the LCD, but I'm still within the return window at Best Buy. Should I just get a really large analog CRT instead, or will I get flicker on that analog connection too? Perhaps try a different make/brand of LCD that has a "regular" DVI connector?

posted by robbie01 to computers & internet (14 comments total)

You can get an external video card for your laptop with DVI out. That would be the only way to get a digital signal from laptop to monitor without hardwiring the monitor to your laptop circuit board. ;)
posted by ChazB at 8:09 PM on June 3, 2006

On closer inspection I believe I may have been wrong. I can only find USB to 15 pin HD D-Sub external cards. You may be SOL.
posted by ChazB at 8:15 PM on June 3, 2006

You could try a better quality VGA cable with more shielding.
posted by kcm at 8:22 PM on June 3, 2006

Sorry for the tripple post, but I found your solution. Its pricy but AFAICT it is the only solution. Linky.
posted by ChazB at 8:22 PM on June 3, 2006

Thanks ChazB. It looks like that VTBook device uses a DVD-I connector, which has four additional pins above and below the "blade" in the DVI connector. So I'm not sure even that would plug into the Samsung's DVI-D port (told ya there were a lot flavors! ;) )
posted by robbie01 at 8:33 PM on June 3, 2006

Getting the converter doesn't really help- it would just replace the A->D converter in your monitor, and might still flicker if the analog output of your laptop was the problem. If your laptop only has analog video outs (VGA), you can't get it to go straight to digital without some conversion.

Adding something like the VTBook is your only option, but first try a better/shorter VGA cable.

This assumes the problem is the VGA connection to the monitor. Have you tried other computers/laptops hooked up to the monitor? Have you tried hooking the computer to different monitors? Something could be broken.
posted by neustile at 8:45 PM on June 3, 2006

The DVI cables with the 4 pins around the flat one are "dual link" - AFAIK it provides higher bandwidth (more bits per time unit) and really isn't needed except when driving *really fricken huge* displays.

I agree with the others - does the monitor flicker when attached to a different computer at a different location or when the laptop/cable/LCD is at a different location?

Recently bought an inexpensive (read: cheap) Acer LCD and I get the same flicker. Being in a different location helps a little bit but there's still that random annoying flicker on dark backgrounds.
posted by porpoise at 9:12 PM on June 3, 2006

You should be able to get a cable that goes from DVI-I to DVI-D. Online somewhere. A quick search of google turned up a Dell OEM DVI-I to DVI-D/VGA splitter for about $5-$10. Also, the VTBook is available on ebay for about $240 new.
posted by ChazB at 10:25 PM on June 3, 2006

kcm is on the right track. I have had this problem with excessively long and badly shielded cables.. Try a better shielded cable and it should improve the situation.
posted by snarkle at 3:36 AM on June 4, 2006

The DVI cables with the 4 pins around the flat one are "dual link"

No they aren't. They're for the a analog (ie VGA) signals. A DVI-D cable will connect to DVI-I without any problems.

Your Samsung monitor is not Dual Link. It may have the pins in the connector, but that doesn't mean they're connected to anything. Again, a standard single link DVI-D cable will work.

A real VGA to DVI adapter costs $200. A $10 one is just routing the VGA signal into the analog pins of the DVI-I connector, and I doubt your monitor is designed to pick up signals from them.

In terms of solving your problem, you need to get the add-on graphics card or try different cables or even a different monitor.
posted by cillit bang at 8:19 AM on June 4, 2006

Interesting, I stand corrected cillit bang.

Is there a label on the DVI cables with the four extra pins? Neither of my DVI-I monitors have the extra 4 holes in them - I've only seen the extra 4 pins in DVI-D cables (having had to return cables a couple of times).
posted by porpoise at 9:25 AM on June 4, 2006

If your monitors don't have the holes, that means they're DVI-D, not I. Similarly, cables with those 4 extra pins present are DVI-I.

(This would all be a lot less confusing if DVI-I was called DVI-A&D, which is much more accurate)
posted by cillit bang at 9:40 AM on June 4, 2006

What it comes down to is the VGA port on your laptop is an analog output, and you're going to get the best results on that monitor with a digital signal. You would be far better served finding an expansion card of some kind (assuming your laptop will take them) that has a digital output, rather than trying to convert the VGA to digital. A VGA signal converted to digital will still have many of the characteristics of analog. Although it might not flicker, it will still be less crisp than a real digital signal. (VGA doesn't have explict pixel boundaries within a scanline, so the monitor and/or converter have to guess, and they don't always guess right.)

I'm with those who suggest trying a high-quality VGA cable first, you should be able to at least get rid of the flicker, but if that doesn't help, you should probably just return the LCD.
posted by kindall at 11:53 AM on June 4, 2006

In terms of testing, I'll try hooking up the LCD to a different computer, and try hooking up a different monitor to the laptop to see if I can isolate which device is causing the problem.

If that doesn't reveal anything, it sounds like the first thing I should try is a higher-quality VGA cable (though the one I'm using doesn't seem like it's particularly "low" quality). I did a Google search and it seems a little ambiguous as to when a VGA cable is significantly better than another, I can't really find an "expensive" one. Does anyone have a specific suggestion for a top-quality VGA cable?

If I can get ahold of one and it doesn't eliminate the flicker, I guess I'd have to return the LCD :(
posted by robbie01 at 2:30 PM on June 4, 2006