Win 7 Machine resets resolution on KVM switch

I have several computers connected via a KVM.

When I switch between machines, machine A) changes resolution from 1280 x 1024 to 1024 x 768. The other machines (one old XP and the other W7) both hold their 1280 x 1024 resolution.

I have been into the registry and set the

HKEY_LOCAL_MACHINE\CurrentControlSet\\Control\GraphicsDrivers\Configuration

Then under the entries there drilled down through 00 and again 00 and set 1280 x 1024 throughout.

It still does it.
Mark PrestonSystems EngineerAsked:
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rindiCommented:
The display resolution is usually set to what the monitor tells the PC it's max resolution is. The problem with many KVM switches is that it hides the monitor from the PC, so the info the PC gets from it is either inaccurate, or nothing at all. If it is nothing, then the PC's resolution is set to a low one which is assumed to work with most displays.

You'll either have to live with this, or find a KVM switch that passes on the display's info to the PC.
Mark PrestonSystems EngineerAuthor Commented:
Yeah, I have read a bit about that, however when the other PCs running through the KVM hold their resolution I presumed that it must be a setting or registry value?

If one PC running W7 holds it's value that surely another running in the same way through the same KVM should be able to?
rindiCommented:
No. it has something to do with the sensitivity of the PC's video card. Some are better at recognizing the display, while some others have a lower sensitivity. With Digital systems (DVI/DVI KDM switches for example), you are less likely to have that issue, than with analog systems (ie VGA/VGA KVM switches).
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Mark PrestonSystems EngineerAuthor Commented:
My system is VGA. But seriously I am trying to suspend disbelief. I have been 'forced' to move on from a perfectly satisfactory XP setup to a W7 setup and find that I have actually gone backwards in that I cannot check my backup and web servers without having to reset resolutions.

Jees, which pins do I have to cut from the VGA cable to stop this 'helpful' communication?
rindiCommented:
It is just how it is. Cutting pins won't do any good.
Mark PrestonSystems EngineerAuthor Commented:
http://en.wikipedia.org/wiki/Display_Data_Channel

That seems to have some info

and specifically:

Disabling DDC
Some KVM switches (keyboard-video-mouse) and video extenders handle DDC traffic incorrectly, making it necessary to disable monitor plug and play features in the operating system, and maybe even physically remove pin 12 from the analog VGA cables[7] that connects such device to multiple PCs.
Mark PrestonSystems EngineerAuthor Commented:
I'm not giving up on this one, there ARE ways to defeat it I'm positive.

There are EDID emulators - but they are pricey. I'd really need to borrow one and verify that it works before going that route.

However VGA connection has R,G & B and their returns, H sync and V sync. So with those connections intact and all others cut the resolution STILL resets!

How does the computer 'know' that anything has happened when all the other lines are cut?
marsiliesCommented:
Is this the same hardware that had Windows XP on it? It's likely a hardware issue, not an OS issue, although it could be a driver issue.

I'm guessing the video adapter is detecting the Monitor "disconnecting" when the KVM switches to another PC. It's losing a signal on all the pins, so it thinks there's no monitor attached, and drops to the lowest resolution. This would happen on a "passive" KVM.

You can try making sure the drivers for your video adapter are up to date. What is the brand/model of the video adapter on the problem PC? You could also try installing a graphics card, so that the PC is using different hardware that may behave better.

You could also try getting an "active" KVM that emulates an active monitor even when switched away.
http://en.wikipedia.org/wiki/KVM_switch#Passive_and_active_.28electronic.29_switches
Most active (electronic rather than mechanical) KVM devices provide peripheral emulation, sending signals to the computers that are not currently selected to simulate a keyboard, mouse and monitor being connected. These are used to control machines which may reboot in unattended operation. Peripheral emulation services embedded in the hardware also provides continuous support where computers require constant communication with the peripherals.

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Mark PrestonSystems EngineerAuthor Commented:
Thanks..

No it's not the same hardware as the XP machine. This is a new PC running W7 although another PC on the system is a new W7 PC and that doesn't suffer the same problem (different manufacturer though).

Interestingly the resolution doesn't change if I pull the cable out of the back of the PC.

I'll check on the manufacturer of the video tonight.

Installing a different video card is also a good idea. I'll check what slots are available tonight also.

Thanks for responding and sorry for my delay in getting back to you. I was away over the Bank holiday weekend.
Mark PrestonSystems EngineerAuthor Commented:
Result!

I found a GeForce video card in the 'recycling' pile of the IT dept.

Installed it and after some reboots and the like it works!

No resolution changes and the display is a little crisper to boot.

Thanks for the great advice.
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