LCD Display

One of the biggest differences between portable and desktop computers is the display. Desktop computers enable both the screen and graphics cards to be changed; in portable computers, both the screen and graphics cards are built into the system. Although most portables feature an external VGA port, which enables a separate monitor to be plugged into the computer, that is the extent of the video expandability of most portable systems. Some recent systems support DualView, a Windows XP feature that enables supported graphics chipsets to use an external monitor as a true secondary monitor instead of as a mirror of or replacement of the built-in display.

Two major types of LCD display screens are used on portables: dual-scan and active-matrix.

Dual-Scan

Dual-scan displays are no longer used on portable computers. However, you might encounter them on older systems. Dual-scan displays are an improved version of passive-matrix displays. Both are controlled by an array of transistors along the horizontal and vertical edges of the display. For example, a 1,024x768 resolution display features 1,024 transistors along the horizontal edge of the display and 768 transistors along the vertical. The transistors send out a pulse of energy, and the individual LCDs polarize at varying angles to produce the picture. Dual-scan screens split the screen into a top half and a bottom half for faster response.

Dual-scan LCD displays are dimmer, have slower response times, and feature a narrower viewing angle than active-matrix screens. The main advantage of dual-scan LCD displays is that, until recently, they have been far less expensive to replace when broken. For that reason, many companies have selected portables with dual-scan displays instead of active-matrix displays. Keep in mind that a portable with a dual-scan display cannot be upgraded to an active-matrix display because the interface to the system is completely different.

Active-Matrix

Active-matrix refers to screens that use a transistor for every dot seen onscreen: for example, a 1,024x768 active-matrix LCD screen has 786,432 transistors. The additional transistors put the "active" in active-matrix, making them nearly as bright as CRT displays. They also offer wide viewing angles for easier use by groups of people and tend to display rapid movement and full-motion video with less blur then dual-scan displays.

Until recently, active-matrix LCD displays were more expensive to replace when broken, and computers with these screens were more expensive to buy initially. However, the widespread popularity of active-matrix desktop displays and improvements in production capacity have enabled active-matrix panels to replace dual-scan in all price ranges of portable computers.

Active-matrix LCD displays also are used an increasing number of desktop computers. Unlike portable active-matrix displays, these displays are attached to the video card or built-in video port the same way that standard CRT-based monitors are. Most plug into the VGA port, but some high-end displays use the DVI port found on mid-range and high-end graphics cards.

Video/Graphics Circuitry

The other built-in portion of the display system is the graphics circuitry; portable computers have built-in graphics that can't be interchanged. There are two methods used for graphics support:

• Motherboard chipsets with integrated graphics

• Discrete graphic chip on the motherboard

What are the differences between these?

Motherboard chipsets with integrated graphics provide adequate performance for business (2D) graphics and cost less than those with discrete graphics, but must use system memory to display graphics. As a result, portables with this design do poorly at displaying full-motion graphics or 3D animations. If you want to increase the amount of memory available for graphics, you might be able to do so by adding additional system memory. Some systems automatically adjust the amount of memory set aside for graphics depending upon the amount of system memory installed. You can sometimes adjust the amount of memory set aside for graphics with a BIOS setting.

tip

To determine if a portable running Windows XP supports DualView, open the Display properties sheet and click the Settings tab. If two monitor icons are displayed, the system supports DualView. Activate it by attaching a monitor to the external video port. If only one monitor icon is shown, DualView is not supported.

Systems that use a discrete graphics chip have faster 3D performance due to these chips' more advanced design and their use of dedicated memory. Recent versions of these chips typically support Windows XP's DualView, which enables an external monitor to be used as a secondary monitor. Typically, you can't increase the amount of graphics memory, but systems with discrete graphics usually have more than enough for both business and light to moderate 3D gaming.

Installation and Removal of LCD Display Panels

LCD display panels built into portable computers are customized for each model of portable computer and require the disassembly of the computer for removal and replacement. You can get replacements from either the vendor or an authorized repair parts depot. Many vendors require that you be an authorized technician before you remove or replace LCD display panels in portable computers. However, the process of replacing the entire LCD display assembly is simpler and might be possible for you to perform in the field.

The details of the process for removing an LCD display assembly from a portable computer vary by model, but you can follow these basic steps:

1. Remove the screws holding the display assembly in place.

2. Remove the cover over the monitor connector.

3. Unlatch the LCD panel from the base unit.

4. Rotate the display assembly to a 90-degree angle to the base unit.

5. Lift the display assembly free from the base unit.

6. Remove the cover over the FPC cable attachment on the system board; the FPC cable transmits power and data to the LCD display assembly.

7. Disconnect the assembly's FPC cable from the system board.

8. Be sure to save all screws, ground springs, and other hardware that you removed during the disassembly process.

caution

Should you do your own LCD display panel replacement? Vendors are of two minds about this. Some vendors provide online documentation, which guides you through the entire process of reducing an intact portable into a pile of parts and rebuilding it. However, this information is primarily intended for professional computer service staff. Portables require specialized tools to deal with their tiny screws and snap-together cases and they contain proprietary parts: If you break an internal drive or an integrated keyboard, you can't run to your favorite electronics superstore for a replacement. You have been warned .

Depending on the vendor, you might be able to purchase a replacement LCD display assembly that can be installed by following the previous steps in reverse order, or you might need to disassemble the display assembly to remove and install the LCD display panel itself. Replacing the LCD display panel (which requires the disassembly of the display assembly) should be performed at a repair depot.

Because of differences in chipsets, BIOSs, and display circuitry between systems with dual-scan and active-matrix LCD panels, dual-scan and active-matrix LCD panels are generally not interchangeable.