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An iMac (Slot Loading) with a sticking power button can generate unpredictable behavior. This article describes the most common symptoms as well as the appropriate steps to take to prevent the button from sticking.
DISCUSSION
- No power - Inability to start up the iMac from either the front power button or the keyboard
- Intermittent shut down or sleep - iMac will randomly shut itself off or put itself to sleep
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.
An iMac (Slot Loading) with a sticking power button can generate the following behavior:
Apple has found that the largest contributor to a stuck power button is an improperly aligned front power-on LED. If the front power-on LED is not centered properly within the inner button, the inner power button can become stuck between the LED and inner bezel resulting in the behavior documented earlier.
LED Alignment Procedure
Refer to the Service Source instructions for additional information on removing the bottom cover.
1. Remove the four screws that secure the bottom housing to the computer and remove the bottom housing.
Position the iMac so that it is directly in front of you. Looking straight on at the inner power button, determine if the LED is centered in the middle of the inner power button as shown in Figure 1.
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| Improperly aligned | Properly aligned |
Figure 1 LED Alignment Examples
2. If the LED is not centered properly, use a small plastic video alignment tool to gently coerce the LED so that it is centered in the middle of the inner button shown in Figure 2. Test to make sure that the inner button no longer sticks by pressing the inner button several times.
Figure 2 Aligning the LED
3. Re-attach the bottom housing.
If the button continues to stick after the LED has been properly aligned, you may have to lightly sand the inner bezel in the area surrounding the inner button to reduce the contact between the inner button and inner bezel.
Inner Bezel Sanding
1. Remove the inner power button so that LED is exposed as shown in Figure 3.
Figure 3 Exposed Power Button
2. Using a 180 grit or higher (Silicon Carbide) wet/dry sandpaper, lightly sand the edge of the lower section of the button recess (indicated by the red arrows) until you have removed any sharp edges on the outside edge of the button recess. The goal is to ensure that there is a slight uniform radius around the entire edge of the button recess.
3. Clean out the inner button recess making sure to remove any debris that may have deposited during the sanding process.
4. Reinstall the inner button and spring.
Test to make sure that the inner button no longer sticks by pressing the inner button several times.