vga to dvi converter: did I buy the wrong one?
September 21, 2013 9:58 AM   Subscribe

Need help troubleshooting my new monitor set up. Problem is my new VGA to DVI adapter

I have:

XFX Radeon HD 7870 2GB GDDR5 Video Card
4+ Year Old VGA Acer Monitor with this VGA->DVI adapter (Let's call him Bob) connecting it to my video card. Works well.
7+ Year OLD VGA Dell Monitor with newly purchased this VGA->DVI adapter (Let's call him Dan) for. This does not work.

Couple of things:
Dell works with Bob (in the DVI slot that Acer and Bob normally use)
Acer works with Bob
Dell doesn't work with Dan
Acer doesn't work with Dan
Bob is old, older then either monitor. Have had Bob for a very long time.

My questions:
Dan was an ebay purchase. Seller listed item as new but it came as is, with no wrapping or packaging of any sort. Is Dan just borked?

Does Dan not work because he has more pins then Bob? Does the pin count in this matter?

Do you think that I bought a defective product, or did I buy the wrong product altogether?

Answers depend on if I ask for a refund or not from the ebay seller. You'll also be pointing me in the right direction of buying yet another vgi->dvi adapter. Thanks!
posted by royalsong to Computers & Internet (5 answers total)
 
There's an analog vs. digital thing going on here. Pin count matters very much.

Here are the adapters that DVI supports. Bob is a DVI-D Dual-Link, where the D is for digital. Dan is a DVI-A, A for Analog. The Graphics card is sending a digital signal. So yes, you need another Bob in your life, as Dan is obsolete as far as your graphics card is concerned. It's time to break up with Dan, or at least put him in a drawer somewhere.

(Don't put him in there with another Dan-- adapters and cables you'll never need anymore, once left in a drawer, will start to either breed or attract more of their kind-- I don't know the mechanism exactly, but it's a real phenomenon.)

Monoprice.com is the place to buy cheap (affordable, not cheap borked) adapters. Use this as an opportunity to save on shipping by ordering all the other cables you need: backup USB cables, extension cables, male-to-male miniplug cables for plugging music into things, etc.

I think you got the wrong product, but I wouldn't put any stock in the lack of packaging on Dan-- it's not uncommon to buy these loose.
posted by Sunburnt at 10:17 AM on September 21, 2013 [1 favorite]


Best answer: Sunburnt's has these a little mixed up. Bob is DVI-A for DVI plus analog VGA. See those four pins on the end with the ground blade between them? Those are your analog VGA signals. Your graphics card has has one connector that will drive both VGA and DVI. You are currently using this for Bob. The other connector on your card will only drive DVI, not VGA.

So the Bob adapter works on the first port which outputs VGA but not the second port if you are driving a VGA monitor.

The question is why are you using adapters at all. I assume that both monitors have DVI inputs. In that case you should just connect DVI directly from the card to the monitors. Don't use the VGA connectors on the monitors.

Now it might be possible that the older monitor only has a VGA connector and no DVI connector. In that case connect the VGA-only monitor to the first port using Bob, the DVI-analog adapter. Then connect the newer monitor, which presumably has both DVI and VGA connectors, directly from DVI to DVI with no adapter.
posted by JackFlash at 12:43 PM on September 21, 2013


It would help to straighten things out if you provided more information.

There are three basis connector types:
Big 28-pin DVI connector
Medium 15-pin VGA connector
Small HDMI 19-pin connector

Can you tell us which of these connectors you are plugging into on the video card?
Which of these are on both ends of your adapters?
Which are available on the two monitors? Is more than one connector on the monitor?
posted by JackFlash at 2:42 PM on September 21, 2013


Best answer: Since the signal comes from your video card and goes to your monitors, it's customary to designate the adapters the other way around: DVI-to-VGA. What the adapter you want does is simply connect some pins from the DVI connector to the right pins on the HD-15 "VGA" connector. Which pin to connect to which pin depends on the pinouts defined in the relevant standards. "Bob" is a DVI-A ("Analog") to VGA adapter. I don't know what "Dan" is supposed to do. It doesn't have the right pin on its DVI side, so there's no way it could pass the signal correctly.

Unfortunately, your graphics card can only create the required analog "VGA" signals on the DVI port marked "VGA" underneath it. The other DVI port cannot produce these signals; this is a common limitation on video cards.

If you want to connect the two monitors to your video card, you will have to connect one of them with a digital connection, either DVI-D (maybe your 4-year-old monitor will have one?) or HDMI (or DisplayPort, but that's a newer standard). If neither of your monitors has a digital input, you're likely SOL; your cheapest option to do dual monitor is likely to be to buy a new one with a digital input (HDMI, DVI-D or DisplayPort/mini-DisplayPort); connect one of your old monitors through "Bob" to the "VGA" DVI port on your card, and connect the new one with an HDMI, DVI or DisplayPort cable.

If you ever need to get another DVI-A-to-HD15 adapter, you can get this one from Monoprice. But with your current video card, it wouldn't do you any good.
posted by Monday, stony Monday at 8:47 PM on September 21, 2013


Response by poster: getting a DVI-D cable for the younger monitor was the solution. Thanks!
posted by royalsong at 5:42 PM on September 25, 2013


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