NEC DPro2070SB, Руководство по обслуживанию

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0 to 5V with the reference of 2.5V by IC102 pin 45 (PWM_DAC), and DC current of +/-100mA (max) is
made to flow to the rotation coil by IC804 pin 2.
This compensation circuit has two functions; (1) User adjustment (OSM display) and (2)
Southern/Northern horizontal magnetic field rotation cancellation.
1.4.3 East-west horizontal magnetic field vertical position canceling function
It is the function that detects the detection voltage change from IC2S0 (geomagnetism sensor unit) by
east-west horizontal magnetic field change, and cancels a changed part of a raster vertical position
automatically.
1.4.4 Corner purity circuit
The corner purity circuit is a circuit to compensate for the color shade and color deviation of the picture
corner. On the rear side of CRT, it is adjusted by DC current flowing to the corner purity coils installed in
the four corners on the display surface.
The compensation circuit is composed of the following five functions of (1) User adjustment (OSM display),
(2) Aging variation compensation, (3) High/low temperature drift compensation, (4) South-north horizontal
magnetic field landing cancel and (5) East-west horizontal magnetic field landing cancel.
(1) User adjustment (OSM display)
The user causes DC current of +/-60mA (max) to flow to the purity coil of each corner according to the
value displayed on OSM.
(2) Aging variation compensation
As the electronic beam collides with the aperture grille, it is thermally expanded and contracted. The
thermal expansion/contraction is varied according to the elapse of the power ON/OFF time of the
monitor. The color shade and deviation of the picture corner thus generated are automatically
adjusted.
The voltage of the beam current supply pin (T701 pin 9) is detected with R723/R724, and the voltage
that detects the time elapse of the power ON/OFF of the monitor is read from the CR charge
(integration) circuit composed of C723 and R738, and CR discharge (integration) circuit composed of
C723 and R737 through IC702 (buffer amplifier) by IC102 pin 26 (CPU_ADC), then, the DC current of
+/-19mA (max) flows to the purity coil on each corner according to the specified control program.
(3) High/low temperature drift compensation
The front panel (glass) is thermally expanded and contracted as the temperature varies in the
installation environments of the monitor. The color shade and deviation of the picture corner are
automatically adjusted. The voltage that detects the temperature variation of the installation
environments of the monitor is read from the environment temperature detection circuit composed of
TH100 (thermistor) arranged near the front panel (glass) by IC102 pin 25 (CPU_ADC), and DC current
of +/-13mA (max) is made to flow to the purity coil on each corner according to the specified control
program.
(4) South-north horizontal magnetic field landing canceling function
North-south magnetic field landing canceling adjusts automatically the color irregularity and color
shading/impurity which are generated horizontal direction served as an opposite direction at the upper
end and lower end of a monitor display side. Detection voltage and a direction of the north-south
magnetic field (IC2S0 pin 5) are detected by IC2S0 (geomagnetism sensor unit) and pin 29
(CPU_ADC) of IC102 reads the detection voltage, and DC current of ±21mA (Max) is passed in each
corner purity coil according to the predetermined control program.
(5) East-west horizontal magnetic field landing canceling function
East-west horizontal magnetic field landing canceling adjusts automatically the color irregularity and
color shading/impurity which are generated horizontal direction served as an opposite direction at the
upper end and lower end of a monitor display side. Detection voltage and a direction of the
north-south magnetic field (IC2S0 pin 4) are detected by IC2S0 (geomagnetism sensor unit) and pin
28 (CPU_ADC) of IC102 reads the detection voltage, and DC current of ±21mA (Max) is passed in
each corner purity coil according to the predetermined control program.