XO Troubleshooting Touchscreen

From OLPC

Jump to: navigation, search

Contents

Symptoms

Slow Response

Certain activities may be slow to respond to drawing actions.

The Paint activity may lag if the fingers are moved quickly or if the system is heavily loaded; a circle drawn with finger may result in a polygon with fewer vertices than expected,

You can either upgrade the activity, or use slower and more careful movements of the fingers. Closing already open activities before starting new activities can be helpful as well.

No Response - Small Fingers

Unusually small fingers or stylii may not be registered.

The area of contact should be 8mm wide, within 1mm of the surface.

You can measure the area of contact by coating a finger with paint and pressing it onto paper, then use a ruler to measure the smallest distance across the marking.

If a child has unusually small fingers, they can either press slightly harder, or at a lower angle (to widen the area of contact), or use a thumb.

No Response - Some Areas

An obstruction to the light guide can make whole sections of the display unresponsive.

Dirt or dust can be captured in the angle between the display and the light guide. Examine the area with magnification. Remove dirt or dust. Do not use an abrasive. Do not use water.

No Response - Anywhere

Check that the laptop was manufactured with a touchscreen front panel assembly; there should be four dots on the hinge cover, and the front panel outermost surface will be 5mm from the display surface. (On a laptop without a touchscreen, the distance is 2mm).

If the laptop does not respond to the touchscreen at all, this usually means a break in the cable between the computer and the touchscreen, which will require repair. How to verify:

  • turn off the laptop,
  • if the laptop is secured, insert a developer key,
  • get to the Ok prompt, and type:
test /touchscreen

Look at the display. If there is a message "missing IR PCB", then the cable between the computer and the touchscreen is broken.

(During during the test, the CPU sends a message to the touchscreen controller chip on the main board, requesting startup. The message "missing IR PCB" means that the touchscreen controller replied, and that the controller was unable to communicate with the touchscreen. The message "failed to boot" means that the touchscreen controller was unable to start.)

Ramp Units

XO-4 ramp units (SKU301 through to SKU306) may have been incorrectly assembled, and the touchscreen may not work.

The clamp for the cable will be missing, or the cable will not be clamped in the connector.

This problem was fixed before mass production began.

These units must be tested before deployment.

Repair is by disassembly of the top, and reconnecting the cable. Or if the clamp is not present, replacing the connector.

See Also

Personal tools
  • Log in
  • Login with OpenID
About OLPC
About the laptop
About the tablet
Projects
OLPC wiki
Toolbox