I have spent the better part of today trying to get an answer to my question through Alienware/Dell, but they are useless. So I am going to try here. I am a computer tech and I am working on an Alienware desktop. It has 2 ATI Radeon HD 4870 X2 video cards installed. When you connect a monitor to the top card and power on, there is no video. Eventually, the video comes up and there are lines through it. After a while, the video goes away (although the monitor light stays green). There is no video on a second monitor attached to the bottom card. The 2 cards are internally connected by a flat cable. I have tried taking 1 card out to see if I can get video on the remaining card, but it didn't work. I can get video if I remove both cards and install a totally different card. So it is obvious to me that one (or both) of the Radeon cards is bad, but it isn't obvious if I need to replace just 1 or both. I have found some on ebay, but they are expensive and I don't want to have the client buy them if it isn't going to work. Dell (in their infinite non-helpful way) said that I could upgrade the video card, but didn't have suggestions as to what. I am not a gamer and I rarely work on gaming systems, so I don't want to recommend a different video card and have it end up not working as well. Is there any way that I can tell which card is bad? I noticed there are lights on the back on the cards, so maybe someone could tell me what they mean and that might help? I appreciate any help I can get. Thank you.

Shouldn't as a computer tech you need to know how t ofix it already instead of asking people on the forums? These kind of people annoy me when they have no knowledge in their job whatsoever.

I would like to thank you from the bottom of my heart for your helpful comment. As a matter of information, I have 17 years experience as a tech and I own the company. However, I don't spend my life in front of a computer screen playing video games. I am not an expert on all things related to computers (and would never claim to be) and I'm certainly not an expert on over-priced video cards. That is why I came here - I was hoping that someone who has a lot of knowledge about this particular card would be able to share some insight into how I can be certain of which card is bad. Because ultimately, I want to do what is best for my client and not waste his money when I should be looking at a different product. I thought that is what these forums are for. Obviously, I was incorrect and they are just places where people can make negative comments about things they probably know nothing about. Thanks again for your help and have a great day.

Well it doesn't really take alot of experience to know the basic knowledge of a broken gpu, which is by the way isn't expensive anymore, just outdated.

But maybe I will try to find some salvation for you and tell that those gpu's are fried and probaly a professional reballer of the chip would do the job quite nicely. Another risky option is just to put heat on the chip which is either using a heatgun directly on the chip or the primitive way on putting it wrapped in tin foil (exluding the chip) in a oven at 200C for 8-10mins

Try each card in the system individually.  Neither requires the other to function. 

Any replacement card that matches their performance will be expensive.  A single 7970 would be largely better in most cases, and runs around $450.

 

Solution:

1. Try the computer with only card "A". Does it work? If yes, it's not broken. If not, it's dead.

2. Try the computer with only card "B". Does it work? If yes, it's not broken. If not, it's dead.

3. If one of the cards work, and the other doesn't, ask the customer if 1 card is enough for them. If not, ask them about the overpriced one on eBay.

4. If both are dead, they should be replaced with

a) One recent, very powerful card

b) 2 recent, whatever cards.

Just forget about replacing both to the same type. It's not worth it. Maybe it's not worth even if one of them is still working. It could be sold.

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CPU: AMD Phenom II X4 810 @ 3250MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 850/1100MHz | Display: Chili Green Vision L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 95 x64 Edition

CPU: Pentium 4 Northwood S478 @ 3200MHz | RAM: 1,5GB DDR 400| MoBo: Gigabyte GA-8S661FXMP-RZ | GPU: Abit Geforce Ti 4200 | Display: Dimarson 19" CRT | PSU: Noname 400W | OS: MS Windows XP Pro, Fedora 18

You could actually end up with the same or greater performance from a 7870, Crossfire/SLI scaling varies widely from 0% to around 90% depending on the game. The third GPU usually adds more to the fluidity than performance. The fourth GPU usually just adds more heat and power consumption than to actual performance. But at four years of extreme heat cycling with a Dell power supply, it's getting about its time.

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Crosshair IV Formula, Phenom II x4 965 w/ Corsair H60, 8 GiB OCZ Platinum DDR3 1600, XFX HD 7970 Ghz, 512GB Vertex 4, 256GB Vector, 240GB Agility 3, Creative X-Fi Titanium w/ Creative Gigaworks S750, SeaSonic X750, HP ZR2440w, Win 7 Ultimate x64