Sony TRINITRON BVM-14G1A Operation And Maintenance Manual page 88

1-8. Half Blanking Switch
The character is half-blanked by the CHAR BLK signal.
1-9. 100 IRE Pulse, SET UP Pulse Insertion
Circuit
To adjust the contrast, the 100 IRE pulse and SET UP pulse
are alternately inserted in the horizontal blanking period of
the R, G, and B signals.
For the R signal, at IC110 (2/3), the 100 IRE pulse and SET
UP pulse are inserted. The level of the 100 IRE pulse is set
by the R 100 IRE voltage. The level of the SET UP pulse is
set by the R SET UP voltage. These two voltages are switched
by WHITE INSERT P by IC113 (1/3), and input to IC110
(2/3).
The same is performed for the G and B signals.
1-10. Blue-Only Switch
In the blue-only mode, the B signal is output instead of the R
signal at IC110 (3/3), and the B signal is output instead of
the G signal at IC310 (3/3).
1-11. Contrast, Bright Adjustment Circuit
The R signal is contrast-adjusted by IC112 (gain control am-
plifier). The R signal output from IC112 and amplified by
Q167 to Q169, input to IC113 (3/3), and the voltage of the
100 IRE pulse is sample-held. At IC114 (1/2), this voltage
and the CONT voltage are compared, and the IC112 gain is
controlled. As a result, the 100 IRE pulse and CONT voltage
becomes equal. Consequently, by varying the CONT volt-
age, the contrast level can be adjusted. The R signal output
from Q167 to Q169 is also input to IC113 (2/3). Here, the
voltage of the SET UP pulse is sample-held. At IC114 (2/2),
this voltage and the GND level is compared to control the
DC bias of IC112. As a result, the pedestal level of the R
signal is fixed at the GND level.
The DC bias of the R signal amplifier (Q167 to Q169) is
controlled by the BRT voltage to adjust BRIGHT.
At IC701 (1/3), the BRT voltage is created by switching the
BRIGHT voltage and BRT CENTER voltage in the period
inserted with the pulse (100 IRE pulse, and SET UP pulse)
and in other periods.
The same is performed for the B and G signals.
1-12. Pulse Insertion Circuit
At IC116, the BIAS REF pulse, DRIVE REF pulse, and char-
acter pulse are inserted in the R signal. The level of the BIAS
REF pulse is set by the BIAS REF voltage. The level of the
DRIVE REF pulse is set by the DRIVE REF voltage.
The same is performed for the B and G signals.
6-2
1-13. Drive Control Amplifier
To prevent the drive current of the CRT cathode from ex-
ceeding the reference value, and the drive voltage from ex-
ceeding the reference value, the levels of the R, G, and B
signals are controlled.
The drive current of the CRT cathode is detected by the cur-
rent of pin 5 of the VIDEO OUT amplifier (IC119). The
current of pin 5 is clamped, I/V-converted by IC123, sam-
pled by IC126 (2/3), and compared with the reference volt-
age (R DRIVE IK) at IC127 (2/2). When the drive current
exceeds the reference value, the signal output from IC127
(2/2) is passed through IC117 (3/3), Q170 to Q172, and in-
put to IC115 (R drive control amplifier) to lower its gain.
The drive voltage of the CRT cathode is detected by the volt-
age of pin 9 of the VIDEO OUT amplifier (IC119). The
voltage of pin 9 is clamped by IC121, sampled by IC126
(1/3), and compared with the reference voltage (R DRIVE
V) at IC127 (1/2). When the drive voltage exceeds the refer-
ence value, the signal output from IC127 (1/2) is passed
through IC117 (2/3) and Q170 to Q172 and input to IC115
(R drive control amplifier) to lower its gain.
The SUB CPU (IC902) sets whether to control the drive
amount based on the drive current (current mode) or control
the drive amount according to the drive voltage (voltage
mode) (IK/V SW). Normally, the SUB CPU operates in the
voltage mode and sets into the current mode during WB ad-
justment. The DRIVE COMP is used for converting the data
of DRIVE V in the voltage mode, and the data of DRIVE IK
in the current mode.
1-14. Clamp Circuit (3)
The voltage of the BLACK pulse of the R signal is sample-
held by IC117 (2/3). At IC118 (1/2), this voltage and the
GND level are compared and the DC bias of the R signal
amplifier (Q174 to Q176) is controlled. As a result, the ped-
estal level of the R signal is fixed at the GND level.
The same is performed for the G and B signals.
1-15. Cut-Off Switch
At IC117 (3/3), the VIDEO TIMING pulse is used to switch
between the R signal and cut-off voltage (–0.3 Vdc.)
The same is performed for the G and B signals.
1-16. VIDEO OUT Amplifier
IC119 is used to drive the R signal cathode of the CRT.
The same is performed for the G and B signals.