marc said:
Hello everybody,
I was wondering whether someone could help me figuring out why I can't
get the second monitor of my system working. The system is a modern
pc, dell 3GHz, with a radeon x600 videocard, running windows XP sp2.
Two monitors are connected to the videocard (one videocard), using one
cable which splits into two connectors. The system recognizes that
there are two monitors, but the second monitor remains blank. I have
switched the connectors and both monitors are working. I have run the
windows troubleshooter and addressed all points but to no avail.
Display drivers are installed and the connection type is pci. Any help
is much appreciated.
Best regards,
Marc
That cable sounds suspicious.
First, there is some background info here:
http://www.playtool.com/pages/dvicompat/dvi.html
Here is a sample picture of an X600:
http://www.ateck.com/catalog/r38-td3b.jpg
The bottom connector is VGA (analog) and there is definitely
only one monitor interface on that connector.
The top connector looks to be DVI-I.
DVI-I consists of two interfaces, a digital interface and
an analog interface. If you connect a "VGA dongle" to a
DVI-I connector, it is possible to extract just the analog
portion of the interface, giving the standard 15 pin VGA.
Functions on there, include the RGB signals that give you the
display, plus the SCLK/SDATA that the computer and monitor use,
so the computer can read the EDID from the monitor and understand
what resolutions it supports.
If you plug a DVI-D cable into the DVI-I connector, then
you gain access to just the digital version of the output.
On a DVI-I cable, normally you use the analog output or
you use the DVI-D output, but you don't use both at the
same time. At least, without deciding what to do about
SCLK/SDATA. I don't think two monitors can share the same
serial interface, but I could be wrong. (I cannot think
of a reason they'd want to support multiple devices on
the bus, but maybe they do.)
So, I'd try connecting one monitor to each of the
connectors shown in the atech.com catalog picture.
Using separate cables.
The video card has two logical blocks inside, for
driving the two monitors, and the faceplate
can have up to three connectors on it. Usually you
are limited to using specific combinations (2 of 3)
of the connectors. And on a DVI-I, you generally only
want to try to use one set of the output signals at
a time, as SCLK/SDATA may be shared, and I don't know
what would happen if you tried to use both. If SCLK/SDATA
only went to one monitor, and not the other, then you
could be in the dangerous situation of sending a higher than
acceptable resolution to one of the two monitors. (Like if
one monitor, the one with SCLK/SDATA, was a 1280x1024 LCD,
and mthe second monitor was an old 1024x768 analog CRT.)
Alternate names for the SCLK and SDATA, are SCL and SDA,
or in this picture, DDC Clock and DDC Data. The key in this
picture calls the DDC Clock and DDC Data, part of "Plug and
Play", as it allows the computer to figure out what the
monitor characteristics are, and I think it only expects
to find *one* monitor.
http://upload.wikimedia.org/wikipedia/en/0/03/DVI_pinout.png
OK, I found an example of your cable here.
http://www2.dvigear.com/dvmatodvfevg.html
I would use only one of those two interfaces at a time.
Actually, I wouldn't use that adapter at all, because it leaves
the signals an open stub, when one connector is not used.
If you need to extract the VGA analog signals, I'd prefer
to use one of the following, because it doesn't do anything
with the digital signals at all. This is a DVI-I to
VGA dongle, which typically comes packaged with certain
brands of video cards. The cheaper the card, the less
likely you are to find one of these included in the package.
I won't buy a video card, unless this is listed as being
in the box (because I hate having to buy one later).
http://www.smarthomepro.com/97346.html
By means of the VGA dongle, you can connect a VGA monitor
to the DVI-I connector. Or if you use a DVI cable, you can
connect a DVI monitor. I'm not really that crazy about that
Y shaped cable, due to the sharing of SCLK/SDATA, and
leaving the unused signals flopping around on the connector
that is not being used. (Maybe the video card is clever
enough to turn off the unused signals, but I don't know
that for a fact. At least with the analog interface, it is
possible for the video card to sense and detect that
something is connected to the analog RGB signal. Since not
all display devices have DDC on them, probing the serial
bus and looking for EDID info, is not a sufficient test
that a display device is connected.)
Paul
