A-65
If the system responds to the paper clip test, the touchscreen or the cabling
between the touchscreen and your test point is at fault. See “Touchscreen
Diagnosis” on page A-65, for further troubleshooting.
• Linearity. If touch data is being reported, but the system linearity is poor, the
problem can be in any touch component. Do not confuse linearity problems
with improper video alignment. Video alignment errors can cause
progressive offsets in the reported touch location versus your actual point of
touch, even in the opposite direction, but never orthogonal to the direction of
movement. Random responses may be due to improper controller setup.
If your problem is linearity and not video alignment or setup, investigate cables
next. A cable with one drive wire (connected to pins 1, 2, 4, or 5 of the
touchscreen) disconnected, or open, will produce non-linearity that gets
progressively worse as you move toward the corner associated with it. This
problem can be verified with an ohmmeter. See “Touchscreen Cables” on
page A-75.
It is also possible for a shorted transient protection component to produce the
same type of symptom. Verify that all four transient suppression diodes are
functional if an open in the cable cannot be found. These components fail
shorted, and should be easy to spot with an ohmmeter. See “Transient
Protection Components” on page A-76.
If linearity is poor in several areas, and you can verify that cables are
satisfactory, the touchscreen may have been damaged by lack of transient
protection. See the following section, “Touchscreen Diagnosis”.
Touchscreen Diagnosis
The easiest way to verify touchscreen failure is by substitution. This eliminates
the need to make any measurements or to concoct a dummy touchscreen.
Touchscreens of any size may be driven by the same touchscreen controller. A
substitute touchscreen may be used on the desktop or held up in front of the
display temporarily to try to verify the source of the problem. The video
alignment will normally differ for each touchscreen.
Before disconnecting the original touchscreen, make sure that transient
protection has not been disconnected. If nothing else is available, ground all five
pins of the touchscreen that has been disconnected while you are substituting
another unit. See “Transient Protection Components” on page A-76, for further
details.
Summary of Contents for AccuTouch 821615-000
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