Description Of Block Diagram - NEC AS120-1 Service Manual

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 CDT when turn on the
power switch.
When you need to degauss while using the monitor,
select DEGAUSS on the OSD menu.
3. SMPS (Switching Mode Power Supply).
This circuit works with power of 100~240V
The operation procedure is as follows:
1) AC input voltage is rectified and smoothed by
the bridge diode (D901) and the capacitor (C905).
2) The rectified voltage (DC voltage) is applied to the
primary coil of the transformer (T901).
3) The control IC (IC901) generates switching pulse
to turn on and off the primary coil of the
transformer (T901) repeatedly.
4) Depending on the turn ratio of the transformer, the
secondary voltages appear at the secondary coil of
the transformer (T901).
5) These secondary voltages are rectified by each
diode (D924, D926, D923, D929, D922, D921,
D920) and operate the other circuits. (Deflection,
Video Amplifier, etc.)
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 Q913, Q915
and IC401 control signal becomes stand-by and
suspend mode. It's power consumption is below 8W.
When no horizontal and vertical sync signal input, it's
power consumption is below 3W.

DESCRIPTION OF BLOCK DIAGRAM

5. X-ray Protection.
This circuit detects the rectified DC voltage comes
from the FBT pin 4. If the high voltage of the FBT
reaches up to about 30kV (abnormal state), H.V
control (IC802) detects. It stops B + voltage supplied to
the FBT (T701), and high voltage is not be generated,
(In the normal state, the high voltage is about 27.5kV.)
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 Signal Cable to the
Micom (IC401).
2) The Micom (IC401) 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 IC402.
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 from
Signal Cable. This circuit consists of the
TDA4841(IC801) and the associated circuit.
8. Oscillating Circuit for D/D Converter.
This circuit generates the pulse wave which has the
horizontal period by taking the output of the
TDA4841(IC801).
9. D/D (DC to DC) Converter.
This circuit supplies DC voltage to the horizontal
deflection output circuit by decreasing DC 190V which
is the secondary voltage of the SMPS in accordance
with the input horizontal sync signal.
10. D/D Drive & Convert Circuit.
This circuit is used for supplying B + voltage to
horizontal deflection output transistor (Q801).
11. Horizontal Deflection Output Circuit.
This circuit makes the horizontal deflection by
supplying the saw-tooth current to the horizontal
deflection yoke.
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