DVI Hotswap; Blank Screen / No Signal (also KVM switch)

Per Hansson

Hiya, most gfx card manufacturers have as far as I know in their infinite wisdom introduced a feature that disables the DVI port of the graphics card when you remove the DVI cable

It also does not enable it when you reconnect the cable, to give a cenario;
To my 8800GTS 512 I have both a TV connected via composite out and a LCD monitor connected through DVI port 1

If I remove the DVI cable, while not even having the TV out activated the TV is made the default monitor, the resolution changed to affect this and usually it messes up and manages to change the display mode from PAL/B into something my TV has problems rendering so I get a black and white picture

Reconnect DVI cable from LCD monitor and I get no signal at all

Things get even funnier in when installing some drivers, example;
I do a fresh Vista x64 install, it's working ok and supporting my LCD's resolution but of course it is dead slow since the standard drivers are crap

We install the latest drivers on nVidias site, it asks us to reboot,
We get the "Microsoft Corporation" start logo, and then bam "no signal"
The very intelligent people at nVidia have now decided that my TV should be the primary monitor and that the DVI output should not even be enabled!

Ignoring this (because it could be a driver bug that nVidia will solve in like 20 years, not at all noticing the dozens of threads that can be found about this with some google searches)
Instead lets think of it this way, we have a DVI KVM switch, and just two PC's conencted to it
We switch the KVM switch from PC1 to PC2, PC1 notices that there is no longer a display connected and disables it's DVI port. ya, for real!
There is a company selling KVM switches that have this problem, they designed a small device that continously sends a EDID signal to the graphics card, so even if a monitor is not connected the graphics card will still think it is, you can see it here;
http://www.microwarehouse.co.uk/catalogue/item/GEFEN087

Now, in Windows XP and 2000 this issue is quite easy to solve I found out, atleast for nVidia users
Under services in Windows disable the "Nvidia Display Driver Service"
The PC will no longer notice that the DVI cable is removed and hotswap, KVM switches etc work just as they should...
This service is linked to a file called "nvsvc64.exe" or "nvsvc32.exe" depending on if your OS is 32bit or 64bit
This file has the description "NVIDIA Driver Helper Service, version 174.31"
Last numbers of course corresponding to your installed driver version. Quite some help this little file provides...
But infact I think it does more, on laptops I think it's responsible for dimming the display when you run on battery etc, but that is of no use for me and my desktop machine...

Anyway, with this in mind I set out to simply do this fix in Windows Vista x64 too... Problem; there is no such service, or for that matter file in Vista.
After some digging around I find out that in Vista this file is instead "nvsvc64.dll" or "nvsvc32.dll"
it has the exact same description as the .exe in XP...

It is called under the registry here;

Code:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
"NvSvc"="RUNDLL32.EXE D:\\Windows\\system32\\nvsvc64.dll,nvsvcStart"

Now I thought that removing this key would disable this "feature"
I was wrong... So I thought maybe it is called from somewhere else, so I removed the file. It didn't help
Windows Vista still notices when I remove the DVI cable and disables it's DVI output!

Now if it wasn't for the fact that my TV that becomes the default monitor is located in another room, with no keyboard or mouse, this might not have been so problematic to troubleshoot further, but it is

So I now ask for your help, have anyone got a clue on how to disable this crap in Vista? Or is it just another thing to add to my list of stuff I hate about Vista?

Per Hansson · 03-22-2008, 14:15 | posts: 86 | Location: Sweden

So, I take it from the many replies that no one else feel this is a big problem?

argobod · 01-25-2009, 17:00 | posts: 1

I just hit this problem, or something similar. DVI/VGA KVM, Vista PC with DVI (only), XP Pro laptop with VGA (only). Monitor supports both (and KVM doesn't convert VGA to DVI) so I use both DVI and VGA cables to the monitor from the KVM console ports.

It worked fine (switching between PC and laptop) when I connected things AFTER bootup, but if PC is rebooted the display goes blank after Windows starts it's boot (BIOS displays fine). Have to hard reset the machine while the monitor is directly connected to get the display back. But the VGA laptop works fine all the time.

So I'm reduced to using the KVM for keyboard and mouse only, and leave both PC and laptop directly connected to the monitor. When I switch between them I have to manually switch the monitor source.

Has anyone found a solution?

viperracing · *Last edited by viperracing; 02-07-2009 at 14:29.*

I have exactly the same problem since a few days since the upgrade to Nvidia ForceWare 181.22 Windows Vista x64

I have these components.
Nvidia XFX 9800GX2 XXX G92
LG 42 "Plasma TV Model: RZ-42PX11
NEW Linkskey KVM-LDV 212ASK: http://www.linkskey.com/detail.php?P...ame=LDV-212ASK

I never had this problem until you connect the Switch KVM for the first time, since the EDID of my TV has gone mad, Now in the Nvidia control panel with only a DVI cable connected me show two monitors/signals analog and a digital sent incorrectly from the EDID of my Tv or poorly received by my Nvidia graphics

I have found that:
-Windows XP 32/64 with 181.22 drivers and this does not happen

-During the installation of Windows Vista does not happen

-Only happens once I've installed the driver Nvidia and is recognized the graphics card, but not when the graphics card is recognized as VGA Standard

-After installing the Nvidia drivers, my monitor looses signal just after the loading screen of Windows Vista in time when enter on the desktop and resolution changes the black screen with no signal until I need disconnect and reconnect cable DVI-DL manually to recover the signal (This is a real nuisance)

-If I leave the windows ready to open the nvidia control panel to when start the system recognizes that I see the display as "Analog Monitor" = Black Screen / not signal but (The system boots but I do not see anything until I connect/reconnect) when Connect/reconnect the DVI to restart the control panel appears as the " Digital Monitor "= Signal correct and functioning properly

-I have proven again to previous versions of Nvidia with which he had never had problems before but I do not solve the problem, I think the KVM switch has been damaged something in my TV

-In addition to all this the Switch KVM then turning off the computers not returns to retrieve the DVI signal and the screen stays black and no signal

-I saw the solution of the Gefen DVI Detective a "scam" because I think that a new switch KVM Linkskey KVM-LDV 212ASK MADE in 04-2008 should be come prepared for this not happen, this option would be acceptable to older KVM-DVI switch but not for new products recent

Thank you very much to "Per Hansson" you have been very helpful to me hope that between us we can find a solution because this is a big problem

Thank you very much, Best regards and please excuse my English

AminoSC · 02-09-2009, 14:54 | posts: 5

I'm having a similar problem. My EDID in my Viewsonic monitor was screwed by a set of Nvidia drivers. now I can't run my monitor with DVI cables anymore. Truly SUCKS! I've tried a million fixes and nothing works.

Hope you have better luck.

yleclerc · 02-09-2009, 15:18 | posts: 617 | Location: CANADA

There is a tool which you might be able to see what is going wrong with the EDID of your monitors

http://entechtaiwan.com/util/ps.shtm

NetSpace · *Last edited by NetSpace; 02-13-2009 at 16:23.*

Quote:

Originally Posted by Per Hansson

So, I take it from the many replies that no one else feel this is a big problem?

Not true. I am having a similar problem. Too bad there are no solutions except to go back to XP. I will do that if I have to.

I hope you read this, my situation.

I have two computers, one has a 9500gt, the other a 7300 nVidia card. I am running dual monitors thru a Startech KVM switch. The second monitor disappears after a reboot and never is seen again unless I remove a cable from the KVM and direct connect to card. then I can switch it back and it works until I need to reboot or somehow loose the dV signal. So if you have found something to fix this, besides the "Gefen ex-tend-it DVI Detective" there is also one made by Startech. I would need 3 of them and at 99$ that is way to expensive after spending 400 on a 4 port dual DVI monitor switch.

I spoke to EVGA and was basically told they did not care and had no plans to support that feature. nVidia has yet to respond and I doubt they will.

I wonder if Riva Tuner has a way to force the DVIE signal to be sent when switching.

Per Hansson · 02-13-2009, 23:18 | posts: 86 | Location: Sweden

No, I found no solution at all
But it is obviously a software issue, since only Vista is affected
Probably due to the DRM crap checking all hardware all the time!

NetSpace · **Tried it! -** 02-15-2009, 16:17 | posts: 3 | Location: Sautee Nacoochee

I looked for that entry in the registry and it was no where to be found. Could later Service packs made this entry obsolete?

Per Hansson · 02-15-2009, 17:55 | posts: 86 | Location: Sweden

No, the nVidia display driver adds that key, maybe they changed it in later versions

I use the driver included with Windows in Windows7, v179.23
With it there are no problems at all to remove and reconnect the DVI cable (in Win7)
I have not tested any other driver, because this is the only one that is WDDM v1.1 capable (you can only get it from Windows Update when running Win7)

Per Hansson · 08-15-2010, 22:53 | posts: 86 | Location: Sweden

I just tested this in Windows 7 x64, the final relese, not an RC like last time
They have now "upgraded" it to work like in Windows Vista

It's impossible to get rid of the behaviour too, simply disabling the service does not help
This time I had two monitors, I turned off the primary one, it worked one or two times, but then it went all haywire, I could hear the device "disconnect and reconnect" sounds playing over and over...
As soon as I turned on both monitors I did get a picture back
This was with a fully patched Win7 machine as of today, with nVidia driver version 257.15
GFX card same as in first post