DVI-D and DVI-I output to VGA monitor?

[ffutures]

Another computer thing, not at all urgent but all suggestions very gratefully received...

My desktop PC has a graphics card with DVI-D and VGA ports. My big widescreen monitor has a VGA port only, and works very nicely on the card; the snag is that I would also like to run a cable to the TV for those occasional moments when it would be useful. Needless to say, the TV is also VGA only, and lower res than the monitor. I REALLY don't want to mess with splitter cables or boxes since they usually screw up the graphics on both screens to some extent, and because this may only see use once or twice a year. Another complication is that the shortest cable run for this is about 20 ft

My idea was to use a DVI-D to VGA adapter and VGA over CAT6 ethernet cable adapter.

VGA over CAT6 worked brilliantly - I can connect e.g. the iBook to one end and the TV to the other and get a perfect picture, got a 15 metre VGA lead for about a tenner. You use CAT6 to get a better signal, CAT5 allegedly deteriorates past 10 metres.

Unfortunately a DVI-D to VGA adapter does not seem to work at all. Not to my monitor, not to the TV, etc., regardless of the cable used. The computer behaves as though there is no monitor present at all.

Before anyone asks, the DVI-D output IS working - if I plug in a monitor with a DVI port and cable it works fine, but that monitor is crappy in other respects so I keep it as an emergency backup. When I try it with the adapter and the VGA port of a monitor it doesn't know it's there.

I'd assume that the adapter or card is borked in some way, but the little netbook I bought recently has a DVI-I dual output; to test it I borrowed a DVI-I to VGA cable from work, we ended up with several spare when we bought some projectors years ago, but that doesn't want to work either - again, it's fine if I connect the netbook directly to the DVI port of the monitor with a DVI - DVI cable.

So... if my experience is typical, DVI output to VGA doesn't appear to work at all, except for things like Ibook adapters which have this sussed in some way. I can only assume that the cheap adapters are intended for plugging a VGA source into a DVI socket, and you need something better to do it the other way. This begs the question of what the netbook guys thought they were doing putting that port on it rather than VGA, but it's far from the only bit of weird design in that netbook.

Anyone got any suggestions?

Comments

[nojay.livejournal.com]

One problem with DVI output (and modern VGA devices too) is that they usually want a handshake between the display and the sending device to sort out resolutions and timing (and possibly HDCP). If the video source doesn't get a handshake then it assumes there isn't any device out there at all and won't attempt to drive it. I had to hook a second monitor up to my desktop PC's VGA output to get the video card to allow me to configure a second display as the driver's configuration system wouldn't let me create it otherwise. Once the device handshakes it only allows resolutions and refresh rates suitable for that monitor but there may be expert-mode overrides if you dig around the configuration windows.

It may be the Ibook is old enough that it doesn't do this sort of handshake and that's why it works over the Cat6-VGA system you've got.

Analogue switchboxes and KVMs limit out at about 1280x1024 due to noise and crosstalk, some better ones with active signal switching and timing signal regeneration will do higher resolutions but cost more. My solution was to source a decent-quality short VGA plug-socket cable and leave that hooked up to the monitor with the socket end dangling. If I want to switch sources I plug and unplug the cables there -- it saves the monitor socket from possible damage and it's easy to access on the desktop rather than fumbling behind the monitor itself.

[ffutures.livejournal.com]

I can understand that - what I can't understand, given that, is why Packard-Bell gave the netbook I bought a DVI socket only! I'm sort of wondering if someone sells a DVI to VGA adapter with configurable resolution and refresh, as with the old Apple monitors.