View Full Version : The vanishing DVI transmitter

07-04-04, 12:46 PM
The GeForce 6800 Ultra reference boards had two Silicon Image Sil178 TMDS chips - one on the front side and one on the back side. To cut costs, it looks like most or all of the 6800 Ultra boards which are actually being sold have only one TMDS chip - there's one on the front side; the back side isn't populated. However, these cards still have two DVI ports.

Does anyone know how this works? Does the NV40 have an integrated TMDS on the chip itself which is connected to the second DVI port? I also noticed that in shipping 6800 GT boards the TMDS chips aren't populated at all. Still, these boards have one DVI port. The only conclusion I can draw is that the NV40 has an internal TMDS.

I wonder if this internal TMDS is good. This is critical for anyone who plans to connect 1600x1200 or 1920x1200 LCDs to this port. In the past, the integrated TMDS in all NVIDIA chips which had them didn't provide the appropriate signal quality for these resolutions.

I'm now thinking that even on the reference boards, the two TMDS chips were actually connected to the same DVI port to achieve a dual-link DVI port (330 Mpps instead of 165 Mpps). You need two Sil178 chips per dual-link DVI port. I noticed that both TMDS chips were located close to the bottom DVI port, so that's probably a dual-link port. The other port was probably connected to the internal TMDS even on the 6800 Ultra reference board.

I'm trying to find out if the 6800 Ultra boards can support two 1600x1200 or 1920x1200 DVI flat panels. I'm not sure because of the likelihood that an internal TMDS is used for one of the ports. Right now I'm using an MSI TI4800 with two Silicon Image TMDS chips (one per port) and it works great, but I would like to upgrade to a faster board. I wish there was a PC version of the new Power Mac G5 Ultra 6800 DDL board. That board has two dual-link (330 Mpps) DVI ports. It costs $599. To get this for the PC, you would need to spend $1600 on a PNY FX 4000.

07-04-04, 03:04 PM
I, too, suspect the 2 Sil178s on the reference board are for a dual-link DVI. From the Quadro FX 2000 on, nVidia has been using a pair for dual-link. At this day and age, I'd think that the internal TMDS should be able to get fairly close to 165MHz.

You may want to try the PNY version, not because it's better but their website claims that: "Dual Single-Link DVI Support
Able to drive the industry’s largest and highest resolution flat-panel displays." At least you'll have someone to blame if it doesn't work for you.

07-04-04, 04:59 PM
Unfortunately, the FX 4000 costs more than I'm willing to spend on a video card.

I agree that it should be technologically feasible to have an integrated TMDS which runs at 165MHz with a good signal. However, neither ATI nor NVIDIA seemed to care much about this so far.

I hope the NV40 has a better TMDS. There's also the issue of the design and the quality of the board, traces, and electronics that sit between the GPU and the DVI ports. The signal can get messed up there. External TMDS chips are typically placed close to the DVI ports. The GPU is further away.

I think this is of particular concern to buyers of the 6800 GT boards since they have only one DVI port which is connected to the internal TMDS. This may not work well with 1600x1200 and 1920x1200 flat panels, and these panels are becoming increasingly popular.

07-04-04, 07:09 PM
My quote is from the PNY Geforce 6800 Ultra. If they claim they support the highest res panel, you should be safe.

Unfortunate for me, nVidia cripples the driver so that I can't use Geforce to drive my T221.

07-05-04, 01:16 AM
I'd love to see an internal TMDS that works well at high bandwidth. Unfortunately, I'm yet to see good stable output from anything other than Silicon Image and Thine TMDS chips. However, I'll give the 6800 Ultra a try.

I hope that the DVI implementation in video cards will improve as high resolution panels become more popular. 2560x1600 30" panels are starting to appear...

07-05-04, 02:51 AM
I hope that the DVI implementation in video cards will improve as high resolution panels become more popular. 2560x1600 30" panels are starting to appear...

What needs to be improved? Dual-link DVI is already here like you said. 2560x1600@60Hz is clocking the links at 130MHz or so which is not that high.

07-05-04, 11:56 AM
The technology is here, but it's either not implemented or not implemented well in most video cards. You need to spend $1600 on an FX 4000 to get two dual-link DVI ports for the PC. The actual TMDS chips are cheap, so this is really annoying.

You have a similar problem if you want to get a card for two 1600x1200 or 1920x1200 panels. This doesn't require dual-link DVI, but it does require a good implementation of two ports of single-link DVI. That's why I've been stuck with a TI4800 all this time, and even this card was rare and extremely hard to get.

07-05-04, 01:43 PM
Tell me about it. All I need is two single-link DVIs at 130MHz or so but they have to be *genlocked*. nVidia cripples the Geforce drivers so that the 2 heads are not synchronized!

I posted here about the reference GF6800 board and the production BFG card. The latter has 1 of the transmitters missing.


09-10-04, 04:28 PM
Might I be a victim of this cost-cutting measure?

After a while (about 1hr) the very black end of the DVI signal (like setting the desktop bgcolor to black) will start showing blue hissing noise/pixels and streaks of blue pixels.

They are NOT memory errors as you cant take a screenshot of them and they only show in the darkest end. For instance, setting the desktop to black and then adjusting brightness by 101% (ie 1%) brings the black up enough to make the hissing disappear. Also it doesnt appear in dos resolutions (bios, post, boot screen etc) or when the nvidia driver is uninstalled and "default vga adapter" driver is loaded.

I can also play games like doom3 at 1600x1200x32 with ease for hours.

I mailed MSI but got no reply.

I looked at the MSI manual and saw they state the "DVI Chip #5" is a little way upleft of the fan connector under the heatsink. Looking into the card I can see that chip is not touching the heatsink AND it has some yellow paper sticker on it! It's a tall chip and perhaps meant to touch the heatsink but the MSI custom copper cooler has dents in it that reach down to the RAM chips and no dents for the two small chips (unknown chip and DVI)

Maybe I could try some DIY fingernail to the sticker, and thermal paste?

The IMPORTANT factor here being my 21" TFT is 1600x1200 native. The chip can prolly handle 1280x1024 even with a damn sticker on it!

ADD: In the pictures here http://www.avsforum.com/avs-vb/showthread.php?postid=4017927#post4017927 the DVI chip is about 2X the size of the MSI DVI chip, and does it indeed have some paste on it?

So far I've used this panel without problems with:

2 different Ti4200

09-10-04, 07:25 PM
Here's a review of the state of TMDS from 2003.10.23.
DVI compliance shootout (http://www.extremetech.com/article2/0,1558,1370516,00.asp)

Essentially this confirms that NVIDIA GPUs have integrated one dual-link and one single link LVDS/TMDS transmitter, and that NVIDIA uses SiI transmitters on reference cards when quality is an issue (they don't trust their own transmitters!)

09-10-04, 07:32 PM
I dont think the tiny silicon chip is a dvi chip at all. There is no dvi chip on the GT I think?

ricercar: do you think a future BIOS upgrade might fix the noise problem I have? I mean it's a relatively marginal problem.. appears under stress/time and in a narrow range of the signal. It's still pretty annoying that my 470€ card has this sort of problem, when my old-a** Ti series worth 30€ has a huge lovely DVI chip and no problems at all.

Right now, after taking the sink off and putting it back, there is no noise again. But after about 30min it starts creeping in again I'm sure.

Edit-- after reading that link I can imagine why MSI wont respond to my inquiry.. they cant offer a product that can handle 1600x1200x32 DVI I bet :lame: