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2.2.4.1
Analysis of the keyboard fault
This handset has 3 side keys. All the keyboard circuits use the scanning method to detect
except the power button .When a button is pressed the scanning signal will be triggered, then
the corresponding row and column will be detected. The function of the key can be identified
according to software definition.
a.
The cell phone can power on
，
but all the keys are invalid.
In general, this situation is caused by some key short-circuit, the equivalent of a
long pressing this button.
At this point ,you should analyze the following first
：
⑴
Check the connector external exclusion and varistor to see if they are
short-circuit.
⑵
Then ,check the connector to see whether it is short-circuit when it is welded.
b.
Failure of a single button
This situation needs to check whether the beneath
of the DOME key is dirty. If the
problem still exists, you have to check whether the circuit is open.
c.
Failure of a few buttons
This situation is usually caused by a short-circuit row or column. Checking the
interface circuit to see if it has open weld phenomena and detect the
disconnected phenomena of the resistance.
