ODD T30 DVI Problem

Message

#1 Post by **Harryc** » Sat May 17, 2008 3:21 pm

I am seeing intermittent flashing pixels or random noise on my 19" DVI LCD when the T30 is docked and connected via DVI single link. It literally looks like several bad pixels, but that is not it because I know for a fact this LCD does not have bad pixels, and I am not seeing this phenomena on any other attached Thinkpad, Macbook Pro, or my desktop. There is no such noise on the T30 LCD itself. I am using a DVI/USB KVM with 6 foot heavily shielded cables. At first I thought I had a bad cable but I swapped those and the problem remained. Now here's the kicker... if I attach the LCD to the T30 directly it works fine, crystal clear. I can obviously get a shorter DVI cable to circumvent the problem, but I was wondering if anyone ever ran into something similar. It's almost like the T30 is putting out a weak DVI signal/s or is not designed to DVI standards. I guess the KVM could also have something to do with it, but then I'd expect to see the problem on all attached devices. DVI is supposed to work on cables up to 25'. I tried (2) different model Docks, same problem. If I set the color depth to 16 bit vs 32 bit the problem disappears. The T30 has an ATI 7500 GPU. I'd try ATI XP drivers but the problem also shows up in OpenSUSE Linux. The problem does not show up if I connect the T30 to the Analog port on the LCD, but again that is not through the KVM, it is a direct connection. I dunno, maybe I am expecting too much from a 5 year old machine, plus the fact that the T30 and similar vintage machines were the first Thinkpads to support DVI and my KVM was produced within the last year. Obviously IBM would not have had an opportunity to test with it.

#2 Post by **RealBlackStuff** » Sat May 17, 2008 5:14 pm

I thought you'd know that the T2x and the T30 do not support DVI.
Even if there is a DVI-port on the dock, the TP still only outputs a VGA signal.

#3 Post by **Harryc** » Sat May 17, 2008 6:40 pm

Well that's an interesting statement seeing as how the T30 outputs a digital signal to my DVI LCD through a single link DVI cable connected to a dock. How could that be? Also, it is listed here as having DVI support -
http://www-307.ibm.com/pc/support/site. ... MIGR-43994
I am running 1280x1024 by the way, and I'm suspecting that even 1280x1024 is pushing the limits for no video noise...

Peter_Peril · #4 Post by **Peter_Peril** » Sat May 17, 2008 9:00 pm

Your reasoning and evidence are pretty strong HarryC; I think you nailed it. Well at the very least you can stick a decent PCI card in your dock and get on with your life. Push that 7500 any harder and you'll be swapping parts

#5 Post by **RealBlackStuff** » Sun May 18, 2008 5:30 am

My understanding was that DVI needed to be supported on the laptop, in order for the DVI-port on the dock/replicator to work.
Guess I was wrong.

Harry, I've hit the jackpot for you!

You want to display at 1920x1200? You apparently CAN!
http://web.mit.edu/~joncox/www/dvi.html

#6 Post by **Harryc** » Sun May 18, 2008 6:22 am

RBS, thanks for the information. It looks like a possible fix for Windows which is good news. Ultimately the fix will be a shorter DVI cable. This is what I will try next because I spend most of my computing time in Linux. The cables that came with the KVM are single-link DVI...19 pins I think. I'll try to find one of those in a short length.

Maccess · #7 Post by **Maccess** » Mon May 19, 2008 2:10 am

The T30 (and T4x) have weak TDMS transmitters. Officially, IBM only supports resolutions up to 1280x1024 with good quality cable.

I've run both a T30 and T43 through a port replicator DVI dock at 1600x1200 resolution. You need to install the latest version of Catalyst control center from IBM and tweak DVI settings.

It might also help to use ATI tray tools to tweak settings, like enable large panel support, which boosts the signal somewhat.

You'll still need a good quality DVI cable, preferably 3ft instead of the usual 6ft.

#8 Post by **Harryc** » Mon May 19, 2008 4:48 am

Maccess, I agree with the weak TDMS transmitter issue. I have a 3 ft. DVI Monster cable on order....we'll see.

#9 Post by **Harryc** » Wed May 21, 2008 9:49 pm

10 hours of straight operation with a 3 ft. Monster DVI cable and the external DVI LCD display is flawless. I'll run it all day tomorrow just to be sure but that looks like the fix.

#10 Post by **RealBlackStuff** » Thu May 22, 2008 6:41 am

Sounds very promising! What model dock/replicator are you using?

#11 Post by **Harryc** » Thu May 22, 2008 6:47 am

It's a mini-dock 2878-10U. I think any dock that is compatible with the T30 that has DVI pass-through would work.

#12 Post by **Harryc** » Thu May 22, 2008 10:27 pm

Day 2, the LCD display is perfect. I'm declaring it fixed and also that you can do DVI very nicely on a T30.

#13 Post by **RealBlackStuff** » Fri May 23, 2008 5:01 am

ODD T30 DVI Problem

ODD T30 DVI Problem

Who is online