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August 2, 2010 8:32 PM   Subscribe

Can Windows be persuaded to ignore lies the BIOS tells it about what video monitors are connected?

One of my classroom computers (Acer desktop, Windows XP, Intel video) has a data projector connected via VGA, and a flat panel monitor connected via DVI. These two devices are supposed to operate in Intel Dual Display Clone mode.

Intermittently since first set up, and increasingly frequently over the last year, the computer has failed to detect the presence of the data projector on morning startup. This happens whether or not the projector is powered up before the computer, and whether or not the computer or projector or both has been physically unplugged from the mains supply overnight.

The result is that only the flat panel monitor gets a display, and Dual Display Clone mode is not offered as an option by the Intel add-ons to the desktop right-click menus.

The workaround we've been using so far is to restart the computer, at which point Dual Display Clone becomes an available option, and then selecting it. This works every time, but needing to restart is stupid and irritating.

I would like to add some startup script commands to force both VGA and DVI outputs to be active and automatically select Dual Display Clone mode. Could one of you kind folk point me to some XP Intel video driver documentation that would help me do that?
posted by flabdablet to Computers & Internet (8 answers total)
This sounds like it's the projector's fault. The cables that people use to hook those things up inside the wall are usually out of spec, so sometimes the DDC data (which tells the computer what sort of display is attached) doesn't make it back to the computer, and the computer assumes nothing is attached. Also, sometimes displays don't send the DDC data unless they are turned on, which confuses the computer.

The first step is to make sure the cable connections are tight and that the cables aren't looped around any radio transmitters (or power cords). The second step is to turn the projector on before you start the computer up.

See if this improves anything; if not, the cable may be to blame. Debug that by connecting the projector directly to the computer with a short, in-spec cable. If this works, the cable is the problem. If not, it's a video card or software problem.

I don't use Windows, so I can't help you there. It's easy enough to force the display on in Linux, so it's *possible* with Intel's hardware. But you might not get anything to work if the cable is just flaky.

(Why does it work sometime if the cable is bad? Randomness. Out-of-spec doesn't mean "guaranteed to not work", it means "not guaranteed to work".)
posted by jrockway at 9:30 PM on August 2, 2010

Response by poster: Yeah, I'm taking it as a given that something is going wrong with DDC (in my experience, something often goes wrong with DDC). This is a 5 metre VGA cable, which is clearly the Wrong Thing (though there is no visible fuzziness or ringing at 1280x800, so it's not a terrible cable) and it's routed through same 1" square plastic wall duct and tubular steel mounting arm as the projector's power cable.

I have recommended that the teacher always

1. Turn the computer and projector off at the wall.

2. Turn the projector on at the wall.

3. Turn the computer on at the wall.

4. Turn the projector on with its power button.

5. Turn the computer on with its power button.

This doesn't seem to help. So I'm pretty much resigned to needing a workaround for intermittently broken DDC data.
posted by flabdablet at 9:43 PM on August 2, 2010

Try installing a driver that has its own control panel e.g. in the tray (so not just the driver). Some of these driver tools have an option to redetect monitors.
posted by oxit at 10:28 PM on August 2, 2010

Response by poster: The Intel one doesn't seem to.
posted by flabdablet at 11:55 PM on August 2, 2010

Does the projector have a DVI or HDMI connector? If so, you could try connecting that one via a digital connection and the monitor via a shorter (I assume it's close to the computer) VGA cable.
posted by Magnakai at 3:45 AM on August 3, 2010

Response by poster: No, the projector's computer inputs are both VGA.
posted by flabdablet at 5:35 AM on August 3, 2010

I had a similar problem where anytime my hdmi connected monitor went to sleep Windows would no longer recognize it. I found a utility program that I could run from a hotkey to force a reset. Not sure if this will fix your problem, but it's worth a shot, and the linked page also lists the (very short) source code for the utility which could be a starting point for something that works for you.
posted by doctord at 6:45 AM on August 3, 2010

Response by poster: It was indeed worth a shot, but it didn't fix the problem.

When I came in this morning, the PC was already switched on, and was still in Single Display mode and refusing to offer Dual Display Clone as an option. Today's quirk was that the VGA output was alive, but the DVI one wasn't.

Anyway I tried that tiny utility but it didn't change anything; it ran, it made the VGA display blink, but Single Display remained the only mode offered by the Intel control panel, and the display that was in use remained the only one on offer. I also tried stopping and restarting igfxsrvc.exe, igfxpers.exe and igfxtray.exe which didn't achieve anything either.

So I eventually restarted Windows.

Interestingly, both screens were active and showing the same image during initial POST and Windows pre-boot (the Windows logo with the throbber bar beneath it) but at the point where the Windows background changes to blue, the DVI panel declared itself to have no signal and went to sleep while the Windows boot sequence continued on the VGA projector. However, Dual Display Clone was then offered as an option after Windows logon, and selecting it brought both displays back into use.

I think what I need is a way to tell the driver to redetect connected monitors or, preferably, unconditionally enable both DVI and VGA outputs. Seems to me that all the things that have failed so far have been fiddling about with app-level stuff that relies on what the driver reports, and not actually making the driver do what I want it to.

Using "Scan for hardware changes" in the Device Manager also has no effect.

The really annoying thing about this fault is that once I've made the displays work on any given day, I cannot get them to misbehave again until the computer has been shut down overnight. Sigh.
posted by flabdablet at 7:00 PM on August 4, 2010

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