If you use an external display connected to your Mac, and if you’ve updated to Leopard 10.5.7, you may experience problems running your external display at its optimum resolution. Problems include the inability to select the correct resolution, blurry text, and in some cases, default video modes that your monitor can not even accept. Plus, you may notice your external display going off every few seconds. Read on for a solution.

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First, keep in mind that there is probably nothing wrong with your external display. And note that these problems affect many displays connected via HDMI or DVI. The problem has to do with video code in 10.5.7 that is incorrectly interpreting your monitor’s capabilities (which are sent from the monitor to your computer). So, erasing your low level video preference files in Leopard will not help because your Mac will simply rebuild those files with the wrong information about your monitor again.

Apple is aware of these problems and is working on a solution which will likely arrive as a Leopard update. In the meantime, here is a simple way to get the correct resolution locked and loaded on your external display.

First, you will need to download SwitchResX Control Panel which you can get here:

http://www.madrau.com/switchres/SwitchResXControl.zip

You can install the control panel application into your Mac settings, or you can simply run it off your desktop. Since you will really only use it once (hopefully) for our purposes, you can put it anywhere.

After you launch SwitchResX Control Panel, make sure you are working with the settings for your external display. At the top of the window, “Settings of:” should be set to your external display.

Next, click on the “Custom” tab/segment. Enter in your desired Horizontal and Vertical resolution settings under the “Active” settings. I would recommend that you leave the rest of the settings untouched unless you know what you are doing with them. Click “Ok” and you’ve just added the custom resolution to your external display. Save/Apply your changes and exit SwitchResX Control Panel.

You will need to restart your Mac in order for the new resolution settings to be available. After restarting, use your normal “Displays” settings in Leopard to select the correct resolution which should now be listed for your external monitor. Keep in mind that Leopard stores your resolution preferences for dual display, mirror mode, and single external display mode separately, so you may need to select your resolution again for each of those modes that you use.

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