Apple iMac G5, 20-inch - Manual (Page 264)

40 - iMac G5, 20-inch Troubleshooting Symptom Charts
When displaying a single color over the screen area, the LCD panel shows one
or more pixels that are not properly lit
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.
LCD Size
(inches) Acceptable Number of Subpixel
Anomalies Replace the LCD Panel
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