Service manual of MT31AS
brightness light source for TV. The part of Decode and input/output can realize the input ports for
TV, and decode the signals. The video signals are outputted to panel by LVDS. The sound signals
driver the speaker by AMP. It is easy to solve the problem quickly if you are familiar with the main
board
’
s elements because you can deduce the issue components by badness phenomenon.
5.1. Power Unit
The power unit
’
s EMC wave filtering concludes two common mode inductances and a Y
capacitance. That can insulated against electromagnetism interference and avoid interference
from Main board to power grid. The resistance of NTC inspects the abnormal temperature and
can fuse the fuse to protect circuits. Full wave rectifier translates AC into DC. HV receive DC 300V.
The DC-DC unit adopts Fly back structure. MOS control the on/off by the power manage IC.
Transformer open and close intermittently. The main grade coupling voltage will be commutated
to VCC 18V supplying for the power manages IC. The secondary coil voltage will be commutated
to 12V and 40V by diode when the main grade is steady. 12V will be feed backed to PWM IC
’
s FB
through TL431 and optocoupler after bleeder circuit. It can adjust GATE to output PWM
waveform. And there can have steady 12V finally.
The waveform of HV test point The waveform of secondary coil
The Schematic diagram of high voltage parts
