Contrast, White Balance, And Brightness Control; Video Bias Control - Mitsubishi Diamond Plus 93SB Service Manual

7.1.4 Contrast, White Balance, and Brightness Control

The MPU (U701) sends an 8-bit control data of contrast, white balance, and brightness to the U201 through
2
the I C bus (SCL, SDA line). The contrast data is used for the simultaneous control of the R, G, B cathode
voltages for the three channels. The white balance data is used to control R, G, B, gains respectively. The
brightness data is used for the simultaneous control of the R, G, B bias levels. Then, the brightness data are
converted from digital to analog (DC voltage 0 to 5V) in the U201. The data from the D/A output pins (14, 15,
16) are respectively output to the bias circuits (B_BIAS, G_BIAS, R_BIAS).

7.2 Video Bias Control

The video signals are amplified at the U204. The bias voltages output from U201 are amplified in the bias
circuit to control the Brightness.
The brightness of the back raster is adjusted by controlling the black level of the CRT cathode, which is the
DC clamp level of the output for the bias circuit. The brightness of this back raster is adjusted by the
brightness. The output from the bias circuit is dependent on the R/G/B bias and brightness. The R/G/B bias
is individually adjusted by controlling the D/A outputs from U201 Pins 14, 15, and 16 through the I
extended from U701.
U201
Pre-Amp
14 15
B-Bias G-Bias R-Bias
B
18
7
G
19
6
R
20
9
16
R217
1
BIAS circuit
R237
2
R257
3
(Fig. 7.2) Video Bias Control
B
3
U204
G
OUTPUT-
2
Amp
R
1
83V Line
R256
D254
7-17
R236 R216
D234
D214
2
C bus
BK
CRT
GK
RK