DESCRIPTION OF BLOCK DIAGRAM
1. Line Filter & Associated Circuit
This is used for suppressing noise of power input line
flowing into the monitor and/or some noise generated
in this monitor flowing out through the power input
line. That is to say, this circuit prevents interference
between the monitor and other electric appliances.
2. Degauss Circuit & Coil
The Degauss circuit consists of the degaussing coil,
the PTC (Positive Temperature Coefficient) thermistor
(TH901), and the relay(RL901). This circuit eliminates
abnormal color of the screen automatically by
degaussing the slot mask in the CRT when turn on the
power switch. When you need to degauss while using
the monitor select DEGAUSS in the SPECIAL on the
OSD menu.
3. SMPS(Switching Mode Power Supply).
This circuit works with power of 90~132Vac/196~264 Vac (50/60Hz).
The operation procedure is as follows:
1) AC input voltage is rectified and smoothed by the
bridge diode (D901) and capacitors (C912,913).
2) The rectified voltage (DC voltage) is applied to the
primary coil of the transformer (T901,T902).
3) The control IC (IC905) generates switching pulse to
turn on and off the primary coil of the transformer
(T902) repeatedly.
4) Depending on the turn ratio of the transformer, the
secondary voltages appear at the secondary coil of
the transformer (T902).
5) These secondary voltages are rectified by each diode
(D922,923,924,925,931) and operate the other circuits.
(Deflection , Video Amplifier ,..... etc.)
The switching IC (IC901) controls input-pulse-width and
generates secondary voltages by sub-transformer (T901).
4. Display Power Management Circuit.
This circuit control power consumption of the monitor by
detecting H and V sync signal.
There are Stand-by and suspend mode.
When no horizontal or vertical sync signal input, the
circuit consists of Q903 and IC913 becomes stand-by
and suspend mode. Its power consumption is below 8W.
5. X-ray Protection.
This circuit detects the rectified DC voltage comes
from the FBT pin 6. If the high volltage of the FBT
reaches up to about 30kV (abnormal state), high
voltage control PWM IC (IC2061) detects it. And PWM
IC (IC2061) prevent output voltage to the gate of
switching FET(Q507).It stops operating primary circuit
of the FBT (T703), and high voltage is not be
generated.(In the normal state, the high voltage is
about 27kV.)
6. Micom (Microprocessor) Circuit.
The operating procedure of Micom (Microprocessor) and
its associated circuit is as follows:
1) H and V Sync signal is supplied from the D-sub to the
Micom (IC271).
2) The Micom (IC271) distinguishes polarity and
frequency of H and V sync.
3) The Micom controls each OSD function signals.(H-
size, H-position, V-size, etc.)
4) The controlled data of each mode is stored in itself.
User can adjust screen condition by each OSD
function. The data of the adjust screen condition is
stored automatically.
7. Horizontal and Vertical Synchronous Processor
This circuit generates the horizontal drive pulse and
the vertical drive pulse by taking sync-signal form the
D-SUB (P208). This circuit consists of the TDA4856
(IC201) and the associated circuit.
8. Oscillating Circuit for D/D Converter.
This circuit generates the saw-tooth wave which has
the horizontal period by taking the output of the
TDA4856 (IC201).
9. D/D (DC to DC) Converter.
This circuit supplies DC voltage to the horizontal
deflection output circuit by decreasing DC 195V
which is the secondary voltage of the SMPS in
accordance with the input horizontal sync signal.
10. Side-Pincushion Correcting Circuit.
This circuit improves the side-pincushion of the screen
by mixing east-west wave to the output of the
horizontal deflection D/D converter which is used for
the supply voltage source (B+) of the deflection circuit.
11. D/D Drive & Convert Circuit.
This circuit is used for supplying B+ voltage to
horizontal deflection output transistor(Q707). This
circuit makes to add side-pincushion correcting signal
to B+ voltage.
12. Horizontal Deflection Output Circuit.
This circuit makes the horizontal deflection by
supplying the saw-tooth current to the horizontal
deflection yoke.
13. High Voltage Output & FBT (Fly Back Transformer).
The high voltage output circuit is used for generating
pulse wave to the primary coil of the FBT (Fly Back
Transformer (T703)). A boosted voltage (about 27kV)
appears at the secondary of the FBT and it is supplied
to the anode of the CRT. And there are another output
voltages such as the dynamic focus frequency.
Summary of Contents for FLATRON 915 FT PLUS
Page 1: ...SERVICE MANUAL LG FLATRON 915FTPLUS MODEL ...
Page 20: ...BLOCK DIAGRAM ...
Page 23: ......
