Mike J.S. wrote:
> Okay, something weird is going on right now. I don't know what triggered it
> but I've been doing a lot of troubleshooting lately, before giving up and
> reformatting my HD (because of another unrelated issue).
>
> The monitor (a "Dell 2407WFP-HC" LCD screen) gets no signal on boot-up until
> Windows is loaded. Only then does it turn on. The screen is connected via
> DVI (looks noticeably better than VGA).
>
> MB is Asus A8N-SLI Deluxe, running latest Asus BIOS for this MB.
>
> Video card is Asus EN6600GT.
>
> ---
>
> Troubleshooting :
>
> When I plug a second simultaneous monitor in the video card's VGA slot (a
> BenQ CRT), BOTH the CRT and the LCD display the full boot-up routine (DOS
> visuals). And of course, the Windows portion.
>
> Leave the VGA slot unplugged (with only the DVI plugged-in), and the whole
> DOS boot-up routine is bypassed by the monitor again. It gets no signal
> until Windows is loaded.
>
> Loading BIOS defaults solves nothing.
>
> What gives? Why can't the DVI slot emit anything until Windows is loaded,
> unless something is plugged into the VGA slot? I need to plug in a 2nd
> monitor each time I want to boot in Safe Mode, or else I can't see the
> menus.
>
The video card has a BIOS add-in module. When the computer POSTs, all of
the add-in modules are loaded. In the motherboard BIOS flash chip, there
might be three add-in modules, for things like PXE boot (network booting),
RAID add-in ROM, and so on. The chip on the video card, also contains
code, and that code is also an add-in ROM. 64KB of memory is allocated for
its use, in low memory.
One of the things the video card BIOS code should do, is initialize the video
card and configure it to support a certain small set of VESA modes. The
BIOS wants to drive the screen at 640x480 or whatever, and there needs to be
a way to load the registers in the GPU, to support that mode.
Now, part of that sequence *could* include the video BIOS code, reading the
EDID information from the monitor. There is a serial EEPROM (electrically
eraseable programmable read only memory) inside the monitor. It is connected
to a serial clock and data interface on the cable. The VGA cable has this
serial DDC interface and so should DVI. As part of the BIOS code loading, the
BIOS code may expect to see sane EDID info, before proceeding. Part of the
purpose of EDID, is so that the video card won't use illegal resolutions or
refresh rates.
Now, there have been cases, where certain monitors and certain drivers, have
resulted in the EDID chip getting corrupted. On the one hand, it would make
a lot of sense, if the EDID chip was read only. The difficulty with that, would
be if the manufacturing people wanted to put a custom serial number, electronically,
for each monitor made. To support that, the manufacturer may leave the chip
read/write. There have been tales of the EDID being corrupted. Once the EDID
is corrupted, connecting your monitor is a lot like connecting your projection
system to the computer - the computer hasn't a clue what is safe. The video
BIOS policy might vary from design to design, as to what to do.
http://www.rage3d.com/board/showthread.php?t=33779480
(More fun with monitors here. Save this one for later)
http://www.geocities.com/jgeneedid/
That is about the only explanation that makes any sense to me, because the
BIOS sequence is not a function of the OS used or any OS settings. Changing
something in the Display control panel, installing a Microsoft Service Pack
or the like, is not going to affect the Video BIOS, motherboard BIOS, or
hopefully, the contents of the EDID chip. They are part of a more primitive
subsystem, that makes decisions before the first sector of the boot is read
off the hard drive.
At the OS level, the OS has a couple choices of info to consult. The OS
can look at the EDID. If the EDID is missing, a second opportunity (for
max res and refresh) can come from the "monitor driver". The "monitor driver"
file is not available from all manufacturers, and an example would be people
who buy 42" LCD TV sets and expect their VGA option to work. TV makers aren't
likely to have a download page with the tiny monitor driver needed.
This utility, will attempt to read the EDID. The above rege3d thread also has some
suggestions.
http://www.entechtaiwan.com/files/moninfo.exe
This is what moninfo reports for my 17" LCD. I presume my EDID is working.
Standard timings supported
640 x 480 at 60Hz - IBM VGA
640 x 480 at 67Hz - Mac II
640 x 480 at 72Hz - VESA
640 x 480 at 75Hz - VESA
720 x 400 at 70Hz - IBM VGA
800 x 600 at 56Hz - VESA
800 x 600 at 60Hz - VESA
800 x 600 at 72Hz - VESA
800 x 600 at 75Hz - VESA
832 x 624 at 75Hz - Mac II
1024 x 768 at 60Hz - VESA
1024 x 768 at 70Hz - VESA
1024 x 768 at 75Hz - VESA
1152 x 864 at 75Hz - VESA
1152 x 870 at 75Hz - Mac II
1280 x 1024 at 60Hz - NEC
1280 x 1024 at 60Hz - VESA
1280 x 1024 at 75Hz - VESA
So, that is my theory, that something has affected the EDID. You'll be able to
verify that pretty quickly, using the above utility.
Finally, if you don't want to screw with the EDID, or contemplate this
problem any longer than necessary, there is another alternative. You mentioned
that connecting both the VGA and DVI, allowed the DVI to work. You can make
a "dummy" VGA connector, to convince the monitor detection feature of the
video card, that a monitor is present. I've done this on another computer,
where the computer would freak if you wake it from standby, and the monitor
happens to be disconnected. I built one of the following, without consulting
this web page, and it worked for me. I didn't need to do more, than terminate
the three color signals, with 75 ohm resistors to ground. The video card
thinks a monitor is connected, although it won't get any EDID from this
"dummy"
http://www.soerennielsen.dk/mod/VGAdummy/index_en.php
HTH,
Paul
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