XO Troubleshooting Display

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HowTo [ID# 141450]  +/-

This is the portion of the XO Troubleshooting Guide for diagnosing problems with the display of an XO laptop.

The display doesn't turn on

Use a strong light shining on the display to confirm that the problem isn't that the backlight won't turn on. If you see text or graphics on the display, the problem is with the backlight.

Use a known good display to check whether the display or the motherboard is broken.

If the known good display also does not turn on, the motherboard is broken and should be replaced.

One half of the display looks bad

Many of these end up being problems with the main display cable (the thick one). The rest are due to display failure.

Is the display cable properly connected ?

Disassemble the laptop to access the larger flex cable from the display to the motherboard. Make sure that it is properly seated in its connector and properly clamped down. The white stripe on the cable should be close to and parallel to the black tab clamping the cable down.

Photo needed here, a closeup of the display connector

If the connector is broken (the small black tab fails to stay in place), the motherboard will need replacement.

Is the display broken ?

Use a known good display to check whether the display or the motherboard is broken.

If the known good display shows the same problem, the motherboard is broken and should be replaced. Typically, this problem is due to a display failure.

The display fades to white

This problem is almost always due to a display failure. Follow the same debugging procedure as with one half of the display looks bad.

The backlight doesn't turn on

If the backlight isn't on in Open Firmware, or when turned up using the display brightness keys in Sugar, check the following:

Is the backlight cable connected ?

Disassemble the laptop to access the small flex cable from the display to the motherboard. Make sure that it is properly seated in its connector, and properly clamped down. If the connector is broken (the small black tab fails to stay in place), the motherboard will need replacement (see temporary repair).

Is the lightbar broken ?

If the cable is well seated, then it is possible that the actual lightbar in the display has failed. Test the laptop with a known good display. If its backlight works, then the original display has a lightbar that needs replacing.

Is the backlight power supply broken ?

If the backlight of a known good display doesn't work, the motherboard needs replacement.

Suspect components are the backlight power supply: U9, D9 (1A schottky), L9 (4.7 uH), R147 (11 ohms), R144 (10K) and Q13 (2N3904 equivalent).

The backlight comes on, but could go out at any time

If the backlight doesn't stay on, there are two possibilities:

• Power management software is dimming the backlight to save power.
• You have a hardware problem. This case is the same as the backlight doesn't turn on

The backlight isn't even

In this case, a vertical pattern of light and dark is seen on the display. The difference between light and dark regions being strongest at the bottom of the screen.

Is the backlight cable properly connected ?

Disassemble the laptop to access the small flex cable from the display to the motherboard. Make sure that it is properly seated in its connector, and properly clamped down. If the connector is broken (the small black tab fails to stay in place), the motherboard will need replacement (see temporary repair)

Is the lightbar partially broken ?

If the cable is well seated, then it is likely that the actual lightbar in the display has failed. Test the laptop with a known good display. If it shows an even backlight, then the original display has a lightbar that needs replacing.

Is the motherboard backlight driver broken ?

If a known good display shows the problem, the motherboard needs replacement.

Check the voltages across R147, R148, and R149 when the backlight is operating. They should be equal. If they are not, replace the corresponding switch transistor (Q13, Q14, or Q15, respectively) with a generic NPN low power switching transistor (2N3904 equivalent).