Apple imac 17in 1ghz Servicehandbuch

20 - iMac (17-inch Flat Panel, 1GHz) Troubleshoot-

Display Symptom Charts

Active-matrix LCD technology uses rows and columns of addressable locations (pixels) that render text 

and images on screen. Each pixel location has three separate subpixels (red, green, and blue) that allow 

the image to be rendered in full color. Each subpixel has a corresponding transistor responsible for turning 

the subpixel on or off.

There are typically millions of these subpixels on an LCD display. For example, the LCD panel used in the 

Apple Cinema HD display is made up of 2.3 million pixels and 6.9 million red, green, and blue subpixels. 

Occasionally, a transistor does not work perfectly, which may result in the affected subpixel being turned on 

(bright) or turned off (dark). With the millions of subpixels on a display, it is quite possible to have a low 

number of faulty transistors on an LCD. Therefore, a certain number of subpixel anomalies is considered 

acceptable. Rejecting all but perfect LCD panels would significantly increase the retail price for products 

using LCD displays. These factors apply to all manufacturers using LCD technology—not just Apple 

products.

To determine whether or not the display has an acceptable number of pixel anomalies, follow the steps 

below:

1.

Set the display image to one of the following colors: all-white display, all-red display, all-green display, 

or all-blue display.

2.

Using a jeweler’s loupe, pocket microscope, or other magnifying device, identify and count each 

subpixel anomaly:

• Bright subpixel anomaly = subpixel that is always on

• Dark subpixel anomaly = subpixel that is always off

3.

Important: Check the number of subpixel anomalies with the following chart:

4.

If the number of subpixel anomalies exceeds the acceptable number listed in the chart, replace the 

LCD panel.

5.

If the number of subpixel anomalies is acceptable, explain to the customer that the pixel anomalies are 

within specifications, and no repair is necessary. 

Important:  Do not release the specifications to customers. Instead, inform them that a certain 

number of subpixel anomalies is considered acceptable, and these factors apply to all manufacturers 

using LCD technology—not just Apple products.

Bright

Dark 

Combination

Bright

Dark 

Combination

17 to 20

up to 4

up to 6

up to 8

5 or more

7 or more

9 or more