RE: re: Monitor Choice (Poll), now Monitor "ringing"

["gary" <gsellani@accesscom.com>]

I would do this gradient test on the primary colors. You're ringing might be
related to some funny convergence problem.

When someone mentions changing the cables, it is only for monitors that have
the BNCs. The BNC connector has a better controlled impedance than the
d-sub. The impedance mismatch causes a reflection on the line, which then
shows up on the screen. I would not advise changing the wiring inside a
monitor.

When I had to test video dacs, I would build a custom PC board with SMAs and
custom matching circuits right on the PCB. [The scopes are 50 ohms, and the
video is 75.] The interface to high speed circuits is critical to meeting
the best performance (i.e. something you would publish in a datasheet even
if you never achieve the same results in real life.)

If you have access to the TDR (time domain reflectometer) with a
sufficiently narrow pulse generator, you can see these impedance mismatches
on the scope, and even locate the impedance mismatch based on the time where
it occurred.

In the dark ages when I was doing these kind of tests, none of the DACs ever
settled to 8 bits in one pixel worth of time. Just another little lie the
manufacturers never talk about.



> -----Original Message-----
> From: owner-scan@leben.com [mailto:owner-scan@leben.com]On Behalf Of
> Hull, Mitchell
> Sent: Thursday, November 15, 2001 11:17 AM
> To: 'scan@leben.com'
> Subject: Was: re: Monitor Choice (Poll), now Monitor "ringing"
>
>
> I have this problem pretty badly-using a G450 graphics card, first with a
> Cornerstone (shadow mask)   , then with my current KDS AV95T (aperture
> grille) monitor.  Most notable with a pure black image-the white
> scroll bars
> on the edge of the Photoshop window (for instance) ghost pretty badly into
> the black.  Its far worse on the left side of the monitor-which is next to
> an old monitor I use for my PS palettes, running off the G450's dualhead.
> Tried moving that monitor some and got no effect on the main monitor
>
> I tried two Cornerstones before sending getting a refund from
> MonitorsDirect
> (nice people), and the KDS didn't do it so badly at first, but 6 months
> later its annoying me quite a lot.
>
> What's the cure-new cable?   I don't think I can swap the cable out of the
> KDS, its hard-wired.  Of course, I DO know a skilled video technician who
> could probably fix something up for me, voiding the warranty in the
> process....
>
> Mitch, on the digest
>
> Date:	Mon, 12 Nov 2001 10:00:17 -0800
> From:	"Paul D. DeRocco" <pderocco@ix.netcom.com
> <mailto:pderocco@ix.netcom.com> >
> Subject:	RE: Monitor Choice (Poll)
> 	> From:	Raphael Bustin
> 	>
> 	> Just out of curiosity, for those of you now
> 	> agonizing over BNC vs. D-sub cables... do you
> 	> have any idea of the video bandwidth that you're
> 	> actually using, or the bandwidth spec of the
> 	> monitor you're using?
>
> I'm using a 21" Nokia with a Matrox Marvel G450 graphics card.
> The card has
> a 300MHz DAC, I believe, and I'm running 2048x1536@71Hz
> <mailto:2048x1536@71Hz> . With conventional cables, I can see the ringing,
> slightly. For instance, if I open a Notepad window, and look at the left
> edge of the white background, I can see a couple faint vertical lines that
> are ghosts of the window's border.
>
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