Auto And Manual Purity Correction (Globalsync) Circuit; Sensor Part - NEC MultiSync FP1370 Service Manual

10. AUTO and MANUAL PURITY CORRECTION (GLOBALSYNC) CIRCUIT

1) SENSOR PART

FP1370 has three sensors to correct poor purity.
A) SENSOR OF EARTH MAGNETIC FIELD CIRCUIT
B) SENSOR OF TEMPERATURE CIRCUIT
C) SENSOR OF CRT BEAM CURRENT CIRCUIT
1-A) SENSOR OF EARTH MAGNETIC FIELD CIRCUIT
EARTH MAGNETIC FIELD CORRECTION CIRCUIT compensates automatically for purity problem of the
EAST,WEST,NORTH and SOUTH magnetic field.
Magnetic sensor (IC4H1) is used in this circuit.
When the magnetic field change, the voltage of IC4H1 pin5 (CNPU pin3), IC4H1 pin6(CNPU pin2) varies.
CNPU pin3 voltage is fed to the A/D converter in IC801 (pin48).
CNPU pin2 voltage is fed to the A/D converter in IC801 (pin47).
And the reference voltage (2.5V) of Magnetic sensor (IC4H1 pin7) is fed IC801 (pin49) too.
CRT face Direction
(Horizontal magnetic field
B :30uT)
H
EAST
WEST
SOUTH
NORTH
+
CRT face (SOUTH)
IC4H1 pin5 Voltage-IC4H1
pin7 Voltage
(Fig.10.1) The example of Magnetic sensor (IC4H1) voltage
B
H
IC4H1 pin6 Voltage-IC4H1
0V
0V
-0.5V
0.5V
IC4H1
8-59
pin7 Voltage
-0.5V
0.5V
0
0