Apple computers: Troubleshooting issues with video on internal or external displays

Important: Many common display issues can be resolved easily by making sure the software on the Apple computer, Apple video adapter, and Apple Thunderbolt cables is up to date by using Software Update or visiting Apple downloads.

Follow the steps below to troubleshoot these issues:

• No video or no signal, image corruption, "snow", or flickering
• Brightness or color isn't uniform
• Pixel anomalies

No video or no signal, image corruption, snow, or flickering

Update the software

Make sure the software and firmware on the Apple computer, Apple video adapter, and Apple Thunderbolt cables is up to date by using Software Update or visiting Apple downloads.

Note: If you're using a display, extender, or adapter not made by Apple, check with the manufacturer for any updates that may be available.

Reset the system

You can reset the Mac's parameter RAM and PMU or SMC. For PowerPC-based Mac mini computers, reset the Mac's PMU. (For Power Macintosh G3, Power Mac G4, or Power Mac G5 computers, check your user guide for the location of the PMU reset button on the logic board). For an Intel-based Mac, reset the SMC.

Check connections

When using an external display be sure to check the following:

1. Confirm the AC power cable or adapter is securely connected to the computer and the cable providing power to the display is also secure.
2. Confirm display adapters are fully seated in their respective connections and that they are supported models for the computer and display. Refer to these articles to assist you with adapter compatibility:
   • Monitor and Display Adapter Table
   • About Mini DisplayPort to HDMI adapters
   • Apple Mini DisplayPort adapters: Frequently asked questions (FAQ)
   • Displays: Mini DisplayPort display must be last in a Thunderbolt chain
3. Remove all display cable extenders and re-test to determine if the issue is resolved.
4. If more than one video adapter is in use—or "daisy-chained"—troubleshoot by using only one adapter. Example: A mini DisplayPort to DVI adapter connected to a DVI to HDMI adapter is an unsupported configuration because there is a series of adapters in use.
5. If available, try using a different display and or adapter (or use a different connector by using DVI instead of VGA, for instance).

Reset the resolution

If the display is set to an unsupported resolution and results in no video:

1. Start up in Safe Mode.
2. From the Apple () menu, choose System Preferences.
3. Choose Displays from the View menu to open the preferences pane.
4. Select any resolution and refresh rate that your display supports.
5. Restart your computer.
   

Brightness and color uniformity

Before evaluating the display for uniformity in lighting or color, the display may need to warm up. Many LCD (Liquid Crystal Displays) use CCFL (Cold Cathode Florescent) backlights. This kind of lighting may require several minutes to half an hour to warm up fully. CCFL backlit displays include the Apple Cinema Displays (20-inch DVI), (23-inch DVI), (30-inch DVI).

Other displays may use LED (Light Emitting Diode) backlighting that can achieve full brightness and color saturation immediately. An example of an LED backlit display is the Apple LED Cinema Display (27-inch).

If you continue to have issues with brightness or color uniformity, check the Displays System Preferences pane. Choose System Preferences from the Apple () menu, then choose Displays from the View menu. From the preference pane you can adjust brightness on internal and Apple external displays on the Displays Tab, and calibrate your display from the Color tab.

Note: Third-party displays may have brightness and additional color adjustments available on the display itself.

Pixel anomalies

If you have concerns about pixel anomalies, refer to these articles for more information: 

• About LCD display pixel anomalies for Apple products released in 2010 and later
• About LCD display pixel anomalies for Apple products released before 2010