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TCL T728 Service Manual
3.4 Charge Circuit
The charging of a battery is under the control of the charging procedure and the power
management Ic U400. With a charger inserting to a charging port, if the handset is placed in
working status, then be in use the charging procedure directly. If a handset is being placed in
power=off status, the 1st pin of U400 detects the voltage signal for charging first, then starts every
circuit of working power supply of U400, the 6th pin of U400 output a charging –detecting signal
CHRDET toward the CPU. The CPU accepts this signal, starts the charging-procedure of a
handset (displaying the icon of charge etc.) and outputs a controlling signal CHRCNTL to the 5th
pin of U400. While connecting a charger, the level of the 4th pin of U401 changes from low to
high and makes the U401 work. And then the current pass through the D414, the beginning
proceeds to charging a battery. When battery is full and the 4th pin of U400 detects the situation,
then the 2sec pin of U400 output a switch-off signal to make the U401 shutdown, the charging
procedure is completed. In the following diagram, the 4th pin of U400is used to detect the degree
of the charging current to avoid the damage of battery while there is a too high current.
3.5 Back light circuit for LCD
T728 is a bar type phone with a B/W LCD. The Back light circuit for LCD is simple, and is
composed with two LBD, which is under the control of an enable signal LCD-BL from MT6305.
3.5.1 KEY LED circuit
The back light for key is controlled by the LED signal from the 41st pin of
U400(MT6305).there is a 100Ω resistance following with every LED in a serial way. When the
LED signal is in a low level, that means the common cathode of the LED(for keyboard ) has a low
level, from but make keyboard light ordered bright.
3.6 Motor circuit
The enable signal for Motor (VIBEN) comes from the GPI015 J5 of CPU MT6205. After the
signal is sent to the 34th pin of U400 MT6305, it is amplified in the inside of U400, and then
th
the 38
is a low level, the motor vibrates; while it is a high level, the Motor will stop vibrating. The
function of D705 is to protect the Motor while there is converse
produced by the vibrating of Motor.
3.7 Audio Part
3.7.1 Receiver & Speaker
The T728
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pin of U400 send out the VIB signal to the cathode end of the Motor. If this VIB signal
phone adopts a way that Speaker & Receiver unite as one. The there are two
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electromotive force
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