Troubleshooting monitor connections for Macs

As the monitor screen is the visual interface for your computer, it's obviously vital that it work properly and show the expected output from your system.

Often when a monitor doesn't display output properly it's because either the monitor or your computer's graphics system is not configured properly or is malfunctioning, but at times it may merely be a matter of an improper connection or a faulty adapter. If your monitor is not showing any output, here are some approaches that can help you determine the nature of the problem.

Recently MacFixIt reader "Jim P." wrote in about a problem in which display output had a pink hue even with multiple cables and system settings:

The first step is to troubleshoot the monitor device itself. Try power-cycling the device to see if merely shutting it off and back on will clear some odd settings on it, and try accessing the monitor's onscreen controls to see if any changes to color, timing, resolution, or brightness settings help the problem. Generally factory-default settings are a good starting point for monitor setups, so if your device supports it then perform a full reset back to factory settings. Doing this will clear the device's firmware settings, which is different from merely turning it off and back on.

Keep in mind that built-in monitors like those on iMacs and MacBook systems do not have device-specific settings that you can access.

If you can, try attaching the monitor to another device to see if it works properly. Many monitors support multiple input types (DVI, VGA, HDMI, and so on), so when troubleshooting with another computer try all connection types to see if one is giving you problems (especially the one that you are using for your Mac).

Another thing to check is the cable and any adapters you are using for the connection. Try different combinations of cabling and adapters to see if one will give you a proper picture. Unfortunately, adapters may not be cheap (especially those from Apple), but they are often the root of display connection problems. In the case of Jim's pink monitor output, the problem ended up being a faulty adapter that he was using.

Besides the monitor, another common source of display output problems is a fault with the computer and the OS configuration. This can be anything from a driver problem to an error in a program or even an overheating hardware component. As a result, you can test problems with your Mac by using any of the following features:

1. Use remote desktop or Screen Sharing
   Enable Apple's Screen Sharing service and then connect to your Mac with another computer on the same network (select the Mac in the Finder and choose the option to share its screen). Screen Sharing will use the Mac's GPU to render graphics, but instead of sending them to the video card's output it will send them to you over the network. This will help test whether or not the system is able to properly process graphics. If you see a garbled display or other faults, then the problem is not with your monitor, cables, or other hardware beyond the graphics card.


2. Boot to an alternate OS
   If you have an alternative operating system (your installation DVD, the Lion restore partition, or a secondary installation of either OS X or Windows), then boot to that OS to see if the problem persists. If it does then this is a strong indication that the problem is hardware-based, instead of being something to do with your OS configuration or drivers.


3. Adjust system settings
   Go to your Displays system preferences and try adjusting various settings that are available. OS X does not provide too many options, but you should at least be able to change the video resolution, and possibly adjust the refresh rate of the monitor. A 60Hz refresh rate is a standard option, but some may have 50Hz or other refresh rates as options that you can try.


4. Calibrate the monitor
   As a last option, if your monitor is giving proper output but only has a tinge of color in its output (such as pink, blue, or green), then you might benefit from calibrating the display. In Apple's Displays preferences go to the Color tab and click the "Calibrate..." button to start up the display calibrator. It is not the best option, but if you stringently follow the directions and match up the color panels correctly then the resulting color profile should get rid any one color dominating the display output. For a more in-depth look, see our how-to on calibrating displays with both Apple's calibrator and the third-party SuperCal program.


5. Perform basic troubleshooting
   Beyond display-specific problems such as the hardware connection, driver issues, and system settings, there may be problems with programs and other settings specific to your unique setup that could be influencing the display and preventing it from working properly. To help root out whether or not these are global issues or account-specific ones, and whether or not third-party hardware or software is causing them, perform a basic troubleshooting routine to see if the problem changes under specific boot conditions.

These approaches to adjusting and managing display output problems are more generic and should apply to most monitor setups, but there are some setups, especially those involving Apple's new Thunderbolt connection, that may have some special requirements. For one, if you are using Apple's Thunderbolt Display then you may not be able to use some other monitors in a dual-display setup. In addition, even though Thunderbolt displays contain DisplayPort protocols, they will only work on Macs that have Thunderbolt connections, which Apple lists here.

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