Service manual
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7
1.3.2 Cut-off control circuit
IC211
Pre-Am
p
IC210
MAIN-Amp
CRT
29
27
25 11
9
8
G
B
R
3
1
5 GK
RK
BK
21 19 20
55
R255B
R255G
R255R
R254R
R254G
R254B
R256B
R256G
R256R
IC102
MPU
D250G D250B
D250R
R250G R250R R250B
215V LINE
G
B
R
G.BIAS
B.BIAS
R.BIAS
BRIGHT
D251R D251B
D251G
3
1
2
IC213
Q251G
Q251B
Q251R
12V LINE
Q250G
Q250B
Q250R
R251G
R251B
R251R
R252G
R252B
R252R
R253R
R253B
R253G
D264
R261
R260
C250G
C250B
C250R
Fig. 5 Cut-off control circuit
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.