Cut-Off Control Circuit; Control Of Brightness; Control Of Bias; Osm (On Screen Manager) - NEC DPro2070SB Service Manual

1.3.2 Cut-off control circuit

IC211
Pre-Amp
19 21 20
12V LINE
The cut-off control circuit consists of Q250R, Q250G, Q250B, Q251R, Q251G, and Q251B, and
simultaneously adjusts 3 colors (brightness), or individually adjusts 3 colors (biases of R, G, and B). The
microcomputer controls both types of adjustment.

1.3.2.1 Control of brightness

To simultaneously adjust 3 colors (brightness), the DAC voltage (0 to 5V, variable) line of microcomputer
pin 55 is connected to the emitters of Q250R, Q250G, and Q250B via IC213. This connection enables
simultaneous control of three TR collector currents and adjustment of the brightness.

1.3.2.2 Control of BIAS

To individually adjust 3 colors (biases of R, G, and B), the DAC output (1.5 to 5.5V, variable) lines (pins 19,
20, and 21 of IC211) are respectively connected to the emitters of Q250R, Q250G, and Q250B via I2C
bus of the microcomputer. This connection enables respective control of three TR collector currents and
adjustment of biases of the R, G, and B.

1.3.3 OSM (On Screen Manager)

IC212 is the OSM (On-Screen Manager), and displays the screens for screen adjustment, etc. The data to
be displayed on the OSM screens is sent to the MPU (IC102) via I2C bus.
G
29 8
IC210
B
25 11
MAIN-Amp
R
27 9
Q251G
Q251B
Q250G
Q250B
Fig. 5 Cut-off control circuit
G
5
B
1
R
3
R250G R250B
D250G D250B D250R
D251G D251B
C250G
C250B
Q251R
Q250R
IC213
1
BRIGHT
1- 7
GK
BK
RK
215V LINE
R250R
D251R
C250R
IC102
55
3
MPU
2
CRT