Service manual

current is limited, and the 380V voltage of PFC will descend. Actually, the current

is limited when the peak value of this board is 0.7V. The pin 4 is a line voltage

detecting pin. It detects the input AC Voltage, and when the 264V voltage becomes

lower to about 80V, the amplifying ratio of the 4th pin is higher, and the duty

cycle of the pin 12 of FPC is higher, the current to the PFC is higher. So when

the input voltage decreases, the power output to C27 will not change. The pin 2

is power detecting pin. The purpose of this pin is:

1) It tries to make the frequency and phase of PFC switch current envelopment

same with input voltage’s, so the PF is close to 1 and the resonance waves are

smallest;

2) It decreases when the duty cycle of PFC increases, increases when detecting

current decreases.

3. When the TV is turned on and the PFC voltage of C27 reaches 380V 2-3%, the

switching power supply PWM begins to work, pin 5 of 4800 is turned on and begins

to charge, when charges to 0.7V, the PWM circuit begins to work, the duty cycle

of PWM cannot exceed 50% when stimulating positively, therefore the duty cycle

of 4800 is limited to 48%, in order to protect switching power. After this, pin

11 output switch pulse signal, makes the transformer T11 work. After rectificated

by D15, pin 6

and pin 7 of the transformer T11 provide a voltage supply, which

is between 13V and 17.5V. To pin 13

(VCC) of 4800, this positive stimulating

transformer just transform voltage. After rectificated by D16, T8 begins to store

energy, C49 filters and outputs 24V,

The 24V voltage regulation process is: 24V provides 2.5V voltage by voltage

division circuit made of R42、R43,then inputs 2.5V to U6, in TVL431, compares

with the internal norm voltage regulation source, when 24V output voltage is low,

U6 pulls down U5 light coupling voltage ,which pulls down the voltage of pin 6

in 4,800 accordingly, increases duty cycle of the pin 11(PWM), so the 24V output

power increases, resulting in the rising of 24V. Contrarily, it drops down.

There is another FS7M0880 switching power supply, when PFC voltage 380V rises,

pin 3(VCC) of U3 FS7M0880 begins to charge by R65, when VCC reaches 13 - 16V,

pin 5 electric capacity begins to charge and to work. Pin 5 and pin 6 of T12 output

voltage accordingly, supplies the power for VCC, the T11 output 5V, +/-12V voltage.

This switching power supply is regulated from 5V; the voltage regulation process

is the same with 24V’s.

5.2、Work Principle of SCALER board

1、SCALER board can: process all video signals; provide the display format which

is accordance with PANEL requirement; finish OSD display and menu operation;

communicate with mini MCU on IO board to receive the key signal and handle

correspondingly.

2、 Features of SCALER board:

The core of SCALER board is single chip PW106. After the outer signal enters

PW106, it is all up to this chip to finish the video decoding of all formats and

picture processing, and finally provide the PANEL-required display format and