iMac: Troubleshooting "No Video" Issues with an External Monitor

This article covers repair procedures for authorized service providers on selected Apple products, but we have published them in the Knowledge Base for the general public for educational purposes. At this time, there are a limited number of repairs that a customer can perform and these are covered under the customer installable parts program http://www.info.apple.com/installparts. If you have not been authorized to perform these procedures, please contact Apple (800-APL-CARE in the USA) or your local authorized service provider to schedule a repair.

DANGER! This procedure exposes you to high voltages that can result in death or serious injury. DO NOT ATTEMPT THIS PROCEDURE IF YOU HAVE NOT BEEN CERTIFIED AS AN APPLE-AUTHORIZED TECHNICIAN.

Symptom

No video

Solutions

Symptom

1. On the original iMac, connect an external monitor (to the connector located on the audio/video interconnect board) to determine whether the issue is in the logic board/mass storage chassis (can assembly) or in the head area (CRT, power supply, analog board). If there is no video on the external monitor, then the fault is generally assumed to be in the logic board area. The presence of a clear external video signal indicates a fault with the analog board. Note: On iMac computers with a video out port, connect the monitor directly to the video out port.

2. Make sure to connect a display that produces video at and supports the resolutions listed below. If the wrong type of monitor is attached to the iMac, it produces no video even if the logic board/mass storage chassis (can assembly) is generating a valid video signal and thus leading to an inaccurate diagnosis of the situation. Apple has seen a number of service providers who have attached older monitors that do not produce a signal on the iMac leading them to replace multiple working parts in search of the fault.

The iMac is capable of producing video only at the following resolutions:

640x480 at 117Hz

800x600 at 95hz

1024x768 at 75hz

Monitors, such as the older sync on green monitors, produce no image when attached to the iMac. Newer monitors that are fixed resolution monitors, even though they may work on a Power Macintosh G3, do not produce a good image on the iMac.

In order to use an external monitor as a troubleshooting aid, the monitor must be one of the newer multiscan, AppleVision, or ColorSync monitors.

Note: If you are still experiencing video problems, refer to:

article 31262: iMac (Summer 2000): Wavy or Flickering Picture on the Screen