Thee DocKtor's Blog

All About Docks

Passive VGA Adaptors Not So Passive

Recently I was asked if I could help with an IT issue that could not be resolved by the contract desktop support team for our Sydney office. An application was not working when the dock was connected.

I noticed straight away there was a passive DVI to VGA adaptor connected to the dock without a display connected, and removal of the adaptor solved the problem.

If you leave a passive DVI to VGA or HDMi to VGA adaptor plugged into the video out port of your dock or your computer, without an active monitor connected to that adaptor, Windows will create what is essentially  a ghost monitor. An HDMi to DVI adaptor will not create this effect.

This can mean an application may seem to fail when the dock is connected and work with the dock disconnected. The last time the display was connected the application was being used on the external display so when the external display is detected, the application opens on that display.

When the application icon is showing in the task bar but the application Window never shows,  the application is actually opening on the ghost monitor. If you watch closely when you repeatedly click the taskbar application icon you will see the application window whisking off to the side of the laptop desktop where the ghost monitor has been created.

You can see the ghost monitor in Control Panel\All Control Panel Items\Display\Screen Resolution. For the following examples I have used a Dual video docking station – ACP71xx

Two external monitors connected to the dock (one turned off) – This is the same as one external monitor connected and turned on plus a passive VGA adaptor in the remaining video port.

 2 External Monitors (0ne turned off)

For comparison this is one external monitor connected to dock and neither active monitor nor passive adaptor in the remaining video port.

 One External Monitor and no Passive

The same effect is created when plugging a passive VGA adaptor into a HDMi or DVI port on your laptop.

My advice is “remove any unused passive adaptors from the dock video ports, and if you have an external monitor attached to the dock, why not use it”

DocKtor Aus

Categories: Usage

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