Blanking Circuit; Spot Killer Circuit; Auto Adjust Blanking Circuit - NEC MultiSync FP1370 Service Manual

4. BLANKING CIRCUIT

The blanking circuit consists of Q7E1 through Q7E3 which amplify the blanking pulse, the spot killer circuit and
the auto adjust blanking circuit.
1) Blanking Circuit
The IC501(DSP) on OSC PWB generates the blanking pulse which are mixed the horizontal blanking pulse
and the vertical blanking pulse and outputs the blanking pulse(VH_BLK) from pin40.The blanking pulse is
amplified by Q7E1 through Q7E3 and are applied to G1.Therefore during the horizontal and vertical retrace
periods, the voltage of G1 becomes low and then the raster is disappeared.

2) Spot Killer Circuit

The spot killer circuit operates when the display is turned off ,the suspend and the off modes. When the
power is on, Q781 is turned off by 8.8V of C781 and the collector voltage of Q781 becomes 137V. When the
display is turn off, the Q781 is activated by the voltage of 8.8V power supply drop. Then the collector voltage
of Q781 becomes 0V from 137V.Therefore G1 voltage is changed to -137V by the change of C783 charge. It
is the same with the suspend and the off modes. Then the raster is cut off.

3) Auto Adjust Blanking Circuit

The auto adjust blanking circuit operates one second when the user proceeds the auto adjust on OSM.
Then Q7K2 is activated by the change of the AS_BLK voltage. Then Q7K3 and Q7K1 are turned off.
Therefore G1 voltage is change to -80V and the raster is cut off.
+220V
SPOT KILLER CIRCUIT
C781 D781
D782 R781
+8.8V
+12V
C7E1 R7E2
VH_BLK
D7E1
-15V
G1 BLANKING CIRCUIT
R785 R786
R784
R787 C783
Q781
R783 D784
R782
R7E4 R7E5
Q7E2
Q7E1
Q7E3
R7E3 R7E7
(Fig.4.1) Blanking Circuit
CRT G1
D783
AUTO ADJUST BLANKING CIRCUIT
R7E6 D7K1
C7E4 C7K1
-80V
8-19
R7K1 R7K3
Q7K1 R7K4
R7K2 Q7K3
+12V
R7K5
AS_BLK
Q7K2