TCL T728 Service Manual
TCL Mobile Communication
CO., Ltd
第
25
页
共
32
页
Chapter 5 Tools and FAQ
5.1 Tools
1
、
Welding equipment(instruments)
：
Iron
、
Hot Air Gun
2
、
Frequency used instruments
：
multimeter (digital)
、
DC power supply(with steady voltage)
3
、
Testing instruments
：
oscillograph
、
frequency analyzer
、
Integrated tester
4
、
Other assistant instruments
：
Personal computer
、
Data cable
、
charger
、
scissor
、
forceps
、
screwdriver
、
plectrum etc.
5.2 No Power On
1
、
Trouble
：
With a battery loaded, no any response while a long pressing the on/off key
—
No
Power On
；
2
、
Analysis: There are several factors to make a handset switching on: 1) the clock circuit
start to work and can offer precise clock-wave.2) the output of the signal of system reset.
3) The output of all kinds of supplying voltage.4) the right software. Any of the factors
having a problem can cause No Power On. The power on circuit of T728 are composed
of CPU
（
U100
）
and power manager(U400).If it is failure to power on, this circuit should
be checked.
3
、
Maintaining steps:
At first, check if there lack any parts or IC, or unreliable contact of ON/OFF KEY.
Then please follow the following steps to remove the trouble:
3
．
1 Connecting the handset to a power, pressing the on/off key, observing the value of
the current. If there is a large short-cut current, the attention should be paid to the
power supply circuit. If there is a normal current, please download the software.
3
．
2
If it still cannot power on after downloading the software, please check if there are
right output of all pins of U400,these output voltage is used to supply for
CPU ,13M circuit, resetting etc.
3
．
3 If the output voltages of U400 are abnormal, please check if there is a 4V or so at the
7
th
,19
th
26
th
47
th
pin, this 4V is supplied by battery. If it is abnormal, should
check the circuit of battery.
3
．
4 If the output voltages of U400 are normal, should think that if the circuit between
CPU and FLASH is normal; At last, consider replace the U100.
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