Purity Correction Part - NEC MultiSync FP1350 Service Manual

2) PURITY CORRECTION PART

2-A) NORTH/SOUTH purity correction
MPU controls output voltage by comparing the sensor voltage (IC801 pin48) with the reference voltage
(IC801 pin49) and GLOBALSYNC OSD.
The D/A converter (IC532 pin16) output center voltage is 2.5V and variable range is between 0V and +5V.
The DC output current flows in the EMF (Earth Magnetic Field) coil.
This current flows to the feedback resistor (R4J5) of IC4J1.
This current is detected as voltage at the feedback resistor.
NOTE) : During DEGAUSS, becomes Low level(D/A converter output voltage is 2.5V), therefore the current
doesn't flow in the EMF coil.
And it prevents magnetization in the CRT.
EMF coil
CRT face
2-B) Four corner purity correction.
MPU controls output voltage by comparing 4 input voltages(IC801 pin47,pin49,pin50,pin51) and
GLOBALSYNC (TOP LEFT, TOP RIGHT, BOTTOM LEFT, BOTTOM RIGHT) OSD.
The D/A converter IC532 (pin14:TOP LEFT, pin8:TOP RIGHT, pin9:BOTTOM LEFT, pin7:BOTTOM RIGHT)
output center voltage is 2.5V and variable range is between 0V and +5V.
The DC output current flows in the corner coil(four corner).
This current flows to the feedback resistor(R4L5,R4N5,R4M5,R4R5)of IC4L1 and IC4N1.
This current is detected as voltage at the feedback resistor.
NOTE) :During DEGAUSS, becomes Low level(D/A converter output voltage is 2.5V), therefore the current
doesn't flow in the corner coil.
And it prevents magnetization in the CRT.
Corner coil
LEFT
TOP
BOTTOM LEFT
(The example of image: Correction of NORTH/SOUTH purity)
CRT face
BOTTOM RIGHT
(The example of image: Correction of four corner purity)
RIGHT
TOP
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