TCL T728, Руководство по обслуживанию, Страница: 27 / 32

TCL T728 Service Manual TCL Mobile Communication CO., Ltd
第 27 页 共 32 页
3 ． 1 Measuring the VDD of the 6
th
、 14
th
、 15
th
、 16
th
、 17
th
、 18
th
pin of LCD, which
is outputted from the 20th pin of U400.If it is abnormal, should check the
relative circuit of these parts.
3
．
2 If the VDD is right, please check if the RST signal at the 2sec pin of LCD is right.
This signal comes from the 24
th
of U400.If it is abnormal, should check the relative
circuit parts.
3 ． 3If all the voltages mentioned above ,should check if the control-signal from the 1st 3
rd
4
th
5
th
of CPU is right. If it is still OK, try to replace the LCD;
3 ． 4 Look carefully if there are abnormal in the periphery circuits. Last thinking to replace
the U100 （ CPU ）。
5.4 No backlight
1
、
Trouble
：
Can be switched on; there are animation and ring tone while turning on the
phone; But no backlight for keypad and LCD.
2
、
Analysis
：
The circuit of LCD and the circuit of Led for keypad compose the backlight
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