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How to stop Vista from auto changing video resolution?

I use a Belkin KVM switch to share a Dell 2208wfp (22" monitor) with a desktop and a laptop.  The video cables from PC to KVM switch are VGA (not DVI), and also VGA from the KVM switch to the monitor.

I normally set the desktop PC to display 1680 x 1050 on the Dell monitor.  When I switch the KVM to the laptop, and then switch back, the video resolution is changed to 800 x 600.  I will then have to manually change it back to 1680 x 1050.  This is annoying enough.  Worse, sometimes, the max resolution is only 1600 x 1200, and I can't find 1680 x 1050.

I have installed the latest drivers from Dell and from Intel.  The Desktop PC is running Vista Enterprise SP1 32-bit, with Intel GMA 945.

Strangely, I don't have a problem with my laptop: when I switch away and switch back to the laptop, the video resolution remains unchanged, which is good.  My laptop is running Vista Business SP1 32-bit, but uses an nVidia graphics card.

I've tried turning off TMM on the Desktop, to no avail.  Would appreciate some help!  Thanks!

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dcscy
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dcscy
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2 Solutions
 
Gregg DesElmsCommented:
This is a well-known problem with KVM switches.  And it seems to only happen with some machines and not others... just as is happening to you.  Or sometimes it happens with one KVM but not others... which may also be happening to you, but you don't know it yet because you've only tried/used one KVM.  

The two most common culprits tend to be either:

a) video drivers (and having the lastest and greatest of them won't necessarily ameliorate this problem) ; or,

b) the KVM has DDC issues (probably in the form of that the OS wants to use DDC, and the KVM isn't configured to (or capble of) properly use(ing) it... isn't passing DDC back and forth, or caching it).  

There can be other culprits, however... including that one of the video cables isn't pinned-out right, or doesn't even have enough of its pins active.  That's a really common one!

You didn't say if it was a passive or active KVM.  Active KVMs are far more likely to be properly using DDC.

       SEE:  http://en.wikipedia.org/wiki/KVM_switch
       SEE:  http://en.wikipedia.org/wiki/Display_Data_Channel

You probably need to open a support ticket with Belkin.  It's not that you can't get an answer here... it's just that Belkin knows its product like no other... and most likely has encountered this before.  It's also a very fast way to learn, straight from the horse's mouth, if the KVM in question can even handle DDC and if that's the likely culprit.

       SEE:  http://www.belkin.com/support/contact/email/technicalsupport/

If it turns out that you need a better KVM, I'll tell you who knows more about this subject than anyone on the planet, and that's the good folks over at BLACKBOX   http://www.blackbox.com/    who have been making and supporting some of the most sophisticated (and often odd-ball) KVM-type devices for the longest time.  They're unbelievable.  You may (or may not, who knows) pay more... but whatever Blackbox sells you (that is, once you consult with them and they're crystal clear what you're trying to do, what equipment you have, and what you've tried already and has failed) will positively work.  Guaranteed.

Others here may have you check/test/try this or that... and who knows, you may find a solution... and maybe even quickly.  But what I've just suggested to you will "gir 'er done" the most quickly and directly.

For whatever that's worth.
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ndaryCommented:
Its all about how your KVM switch handles DDC, What model of Belkin KVM switch do you use? is it a CAT5 switch with dongles or has 3in1 cables from the KVM switch to the computers?

DDC is short form for Display Data Channel. It is a VESA standard for communication between a monitor and a video adapter. Using DDC, a monitor can inform the video card about its properties, such as maximum resolution and color depth. The video card can then use this information to ensure that the user is presented with valid options for configuring the display.  

If your KVM switch do not support DDC then what happens is when you switch to another port the PC may change his native resolution. on Windows XP & Above there is no option on the control panel to disable plug and play monitor detection, you may want to search the web for a work around of doing this.
PIN #12 on the monitor HD15 connector is responsible on the automatic monitor detection. i did not try to check yet how Vista will behave with PIN12 is missing.. but windows XP will disable its  plug and play monitor detection.

If your Belkin switch is a CAT5 switch with PS/2 or USB dongles then it support DDC programming, look in the user manual to find out how you can update your Monitor DDC information into the dongles..

i hope you will find the information above helpful.. Good luck...  
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ChazzFXCommented:
I'm having the same problem as dcscy...with a Vista-64 desktop and an XP-Pro laptop. I have a pair of Samsung 24" LCDs that I switch between the two systems using IOGear DVI kvms that I've had for about 6 mos.
I've talked to the tech support people at IOGear who recommended that I purchase newer more expensive kvms to resolve the problem.  The expense is not worth it, especially to replace devices that are as new as mine.
My question is...isn't there a way to get Windows to stop auto-reconfiguring my displays every time I swich between systems?
TIA...Chuck
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ndaryCommented:

Since dcscy is located in Singapore, I would recommend him to go to Simlim and get a VGA (HD15) cable extender for couple of dollars and try to remove Pin 12 from the male end.. this should remove the monitor plug & play signals.. more info can be found here: http://en.wikipedia.org/wiki/VGA_connector  
 
ChazzFX you are using a DVI connector i haven't tried this with a DVI connector, but if you use DVI-I or DVI-A you can go from DVI-I/DVI-A to HD15 then remove pin 12 and back to DVI...
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ChazzFXCommented:
Thanks ndary. Could you please clarify what I'm seeing in the WikiPedia?  In the location you cite, under "The pin 12 problem" it says:
"The solution is to remove the pin from one end of the VGA cable and to disable any plug and play for the monitor."
This would indicate that the hardware solution is not sufficient.
However, in http://en.wikipedia.org/wiki/Display_Data_Channel, the "Disabling DDC" section states:
"In these circumstances, it may be necessary to remove pin 12 from the monitor VGA cable, to disable plug and play monitor detection."
It then goes on to describe a software solution in XFree...leaving the impression that the hardware & software approaches are either/or solutions.
Can you confirm which is correct?
TIA...Chuck
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ndaryCommented:
You can tell Linux to disable the DDC with a software command (in xorg.conf script)...  

for windows XP or Vista i am not aware of a software hack (in the registry or other) that can do the same.. probably because its different for each Display card driver..
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dcscyAuthor Commented:
Thanks for all your comments and advice!  I was away on a trip and just got back, hence no reply from me.  Fortunately, my trip was devoid of that swine flu stuff....

Anyway, I'll check out all your advice to see what works for me.  Thanks again!
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dcscyAuthor Commented:
Ok, I've found out that mine is a Belkin Flip USB w Audio:

http://www.belkin.com/flip/

I've downloaded and installed Belkin's driver + software for this device.  It looks like an Active KVM.  The problem is now more inconsistent: whereas previously the resolution will go down to 800x600 every time I switch, now it does so only intermittently.  That is, resolution is unchanged some of the time, but is reduced at other times.  I don't discern any pattern to this.

Looks like I may need to try pulling out pin 12.....

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ndaryCommented:
I posted a working solution that require a hardware mod to the VGA cable.. the last post from the author is that he will try it (that was in May)!?
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