B Board - Sony TRINITRON BVM-D9H1U Maintenance Manual

6-2. B board

1. Clamp Circuit (1)
The signal that is selected by the option board is input to
CN301.
IC300 (1/3) (analog switch) is turned ON by the Y-CLP-P
pulse. As a result, the pedestal voltage of the Y/G signal is
sampled-and-held. In IC303, the sampled-and-held voltage
and the reference voltage (Y/G BLACK voltage) are
compared so that the error voltage is used to control the
bias current of the Y/G signal clamp amplifier (Q300 to
Q302) so that the pedestal voltage of the Y/G signal is
clamped to a fixed voltage.
The same clamp operation is performed for the PB/B and
PR/R signals but the C-CLP-P pulse is used as the clamp
pulse.
2. Matrix Circuit
The Y, R-Y and B-Y signals are converted to the R, G and
B signals by the matrix circuit during the Y/PB/PR mode.
IC306 is the Y-level adjustment amplifier. IC307 and
IC308 are the chroma level adjustment amplifier. The R-
signal is generated by adding the Y-signal to the R-Y
signal that has passed IC400 (PR gain control amplifier).
The G-signal is generated by adding the R-Y signal that
has passed IC400 (PR gain control amplifier), the B-Y
signal that has passed IC401 (PB gain control amplifier)
and the Y-signal that is inverted and amplified. These
signals are added at Q463. The B-signal is generated by
adding the Y-signal to the B-Y signal that has passed
IC401 (PB gain control amplifier).
3. RGB Selector Switch
IC1300 (1/3), IC1302 (1/3) and IC1303 (1/3) are the
selector switch selecting either the RGB signal or the
YPBPR signal (matrix circuit). Output of the selector
switch is R, G and B signals.
4. Clamp Circuit (2)
The R-signal is sampled-and-held by the timing pulse of
the deflection system.
IC1305 compares the sampled R-signal with the reference
signal. The error voltage of the comparator controls the
DC bias of the R-signal amplifiers (Q1300 to Q1302) so
that the pedestal level is kept to a constant DC level all the
time. The same clamp operation is performed in the G and
B signals in the same way.
6-2
5. OSD Insertion Circuit
The on-screen display of the R-signal is realized by
inserting the OSD blanking with IC1300 (2/3) and by
inserting the OSD characters with IC1304 (1/3). The
WINDOW signal that is used during the AUTO W/B
adjustment is also created by the character generator, and
uses the same signal line in the same way of the character
display. The same insertion operation is performed in the
G and B signals in the same way.
6. CUT-OFF Circuit
Cut-off of the R-signal is performed by IC1304 (2/3, 3/3).
The same cut-off operation is performed in the G and B
signals in the same way.
7. CXA1739 Peripheral Circuit
The RGB signal is input during the normal operation and
the color difference signal is input during the blue-only
mode.
8. ABL Circuit
The ABL circuit consists of Q1460 for ABL, and Q1461
for BRT ABL.
The ABL voltage from the deflection block is input the
respective emitters of Q1460 and Q1461. The voltage-
divided DC voltage of the ABL signal is input the respec-
tive bases of Q1460 and Q1461. Their collectors are
connected to IC1401 pin-46 (PIC CONT) and pin-7 (BRT
CONT) respectively. When these transistors are turned on,
the ABL operation can be performed by decreasing their
respective control voltages.
9. AUTO CHROMA PHASE
The signals that are output from IC1401 are selected by
IC2380. Only the sample pulse portion of the selected
signal is sampled by IC2381 and is compared with the
output by IC2382. The error signal from the comparator is
fed back to DAC through IC2383 and automatically
controls the PB LEVEL or the R LEVEL until the output
agrees with the sampled level.
BVM-D9H1U/D9H5U/D9H1E/D9H5E/D9H1A/D9H5A