Blanking Circuit; Spot Killer Circuit; Auto Adjust Blanking Circuit - NEC MultiSync FP1350 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
Q781
C781 D781
D782 R781
+8.8V
+12V
Q7E1
C7E1 R7E2
VH_BLK
R7E3
D7E1
-15V
G1 BLANKING CIRCUIT
R785 R786
R784
R787 C783 D783
R783 D784
R782
R7E4 R7E5
R7E6
Q7E2
C7E4
Q7E3
R7E7
(Fig.4.1) Blanking Circuit
CRT G1
AUTO ADJUST BLANKING CIRCUIT
R7K1
Q7K1
D7K1
C7K1
R7K2
-80V
8-18
R7K3
R7K4 R7K5
Q7K3
Q7K2
+12V
AS_BLK