Solving glitches on a HIS Excalibur Radeon 9600 Dual DVI

video card flicker capacitor

===== Introduction =====
This posting shows a solution against glitches or disturbing horizontal lines on an agp HIS Excalibur Radeon 9600 Dual DVI graphics card and maybe applies to other cards as well. The card produces on the display, attached to the second output strong artifacts while playing a video or even just by moving a window at one of the two screens. The problem is worse in Linux (Ubuntu 8.04) than in windows XP. Note that the second output is the DVI connector, situated closest to the THine THC63DV164 DVI transmitter.
Some people say it's driver and timing related. While this may be true and solved with other settings or drivers, the real problem is the graphics card is fed with a too electrical noisy power supply. Therefore, a true solution is improving part of the power circuit at the graphics card. Where the electrical noise is coming from is not being covered in this thread, but it probably has to do with the motherboard architecture and chosen components. Please see below for more details.

===== The card and maybe similar cards to which the problem applies =====
* His Excalibur (Platinum) Radeon 9600 Dual-DVI 256MB Videocard with AGP slot. Other spelling variants of the same card are: HIS Excalibur Radeon 9600 Dual DVI, HIS 9600 Dual DVI


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Image showing the concerning graphic card


===== References to this radeon card and some variations =====
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* General info
* Active cooling: **broken link removed** (Cooling is only present on prototype/pre-series production models)(See: His-R9600-Dual-DVI-Seite1.shtml)
* Passive cooling with a Silicon Bridge DVI compliant transmitter: SB10172AB. See: His-R9600-Dual-DVI-Seite1.shtml (Transmitter is only used for the 2nd DVI output)
* Passive cooling with a THine Electronics DVI compliant transmitter ic from THine Electronics: **broken link removed** (Datasheet; Transmitter is only used for the 2nd DVI output)

===== Searching the internet for clues =====
Before experimenting myself, I searched the internet for solutions from others. It showed several people had the same issues with their graphics card.

===== References to card related problems =====
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* radeon; can't do dual-link tmds, or second tmds transmitter ...I have a picture over the DVI now, but it flickers pretty badly...
* ...The LCD still displays the vertical lines but I'll assume that goes away once loaded into and OS...

===== Related references to cards from other brands =====
I found this problem is not only ATI/AMD related, but NVidia chipsets also seem to suffer from this problem, according to a google search with the following terms: "dvi output" "horizontal lines" "dual dvi"
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===== Linux =====
The artifacts with the HIS videocard with RV350 chipset, tested with Ubuntu 8.04, are worse than under windows. While playing a video file on the first screen, the 2nd screen is showing artifacts quite heavily.


===== Experiments =====
Below you can find the steps I took to tackle the problem.

===== Video memory decoupling =====
Initially I suspected glitches were caused by jitter on data from video memory. At resolutions below 1600x1200 the video was fine on both outputs. The glitches would only manifest at high resolution at or above 1600x1200 pixels. Because at higher resolution, bandwidth is higher, memory timing might be more critical. If so, a cleaner power may solve the problem. So I added extra 100nF decoupling capacitors on top of 4 of the 8 memory chips.

===== Increasing video memory voltage =====
As decoupling did not change anything at all, I had to look further. A second experiment would be slightly increasing the memory voltage, which might give the memory chips faster access. I increased the voltage from 2.50 Volt to 2.55 Volt, by adding a resistor divider at a LM431 reference voltage ic (SOT-23). However, after testing, it seemed the voltage increase did not improve anything at all.

===== Inspecting DVI transmitter =====
Because from the two DVI outputs, only the second one had problems, it crossed my mind that somehow a memory timing issue would not be a logical explanation. If it would be, then likely both outputs would suffer and not only one of them. Due to the differences in the DVI output circuitry, it made even more sense that the problem would be in something specific one of the circuits had which the other didn't have.
So I started to measure power supply voltages around the DVI transmitter, a THine THC63DV164. At the closest capacitor (C1421), I measured 3.3V with about 200mV noise, which was far too much in my opinion.

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Location of THC63DV164 DVI transmitter and capacitor C1421


===== Solution =====
To solve the problem with glitches, reduce the noise at the 3.3V power supply, being fed to the DVI transmitter. The easiest thing is to replace 47uF capacitor C1421 with a larger one. Please note the small yellow arrow, pointing to this capacitor at the picture below.


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Modification of C1421

I tried several types of capacitors and it seemed that at least a capacity of 470uF was necessary. The voltage across the capacitor is only 3.3V, so most capacitors will be fine. It's very critical that the capacitor should be a low-esr type. Smaller capacities and other kind of capacitors may not filter the power supply enough -I tried several ones, and they simply did not work-.
You may even improve filtering slightly, by adding a small smd ceramic capacitor (at the bottom) of about 100nF. The easiest replacement capacitor I could find and which would fit as well, was a 1000uF 6.3V capacitor from an older motherboard. The noise I measured was now less then 10mV.

Although this card is a bit dated and this article may therefore appear a few years late, I hope this information may be still helpful.