Circuit Descriptions; Bk Board - Sony BVM-D32E1WA Maintenance Manual

Section 6

Circuit Descriptions

This section describes the circuits of the following boards used in the BVM-D32E1WA/D32E1WE/D32E1WU.

6-1. BK Board

6-2. PA Board
6-3. BC Board
6-4. G Board
6-5. E, EA Board
6-6. D1 Board
6-7. BUF2 Board
6-1. BK Board
1. BK Select Switch
When the BK SELECT signal is "Low", the Y/G signal of the Y/G terminal (TB1) input is input to IC100 via the buffer
amplifier (Q100, Q102). When "High", the 2Y/2G signal of the 12B terminal input of CN1 is input to IC100.
In IC100, input switching with the Y/G signal is performed at the 11B terminal input of CN1.
The same is performed for the PB/B and PR/R signals.
2. Clamp Circuit (1)
The analog switch (IC100) is turned ON by the Y–CLP–P pulse. As a result, the pedestal voltage of the Y/G signal is sample-
held. In IC101 (1/2), this voltage and the reference voltage (0 Vdc) are compared to control the bias current of the Y/G signal
clamp amplifier (Q103 to 105) so that the pedestal voltage of the Y/G signal becomes 0 Vdc.
The same is performed for the PB/B and PR/R signals.
3. W B INSERT Pulse Insertion Circuit
To adjust the levels of the PR and PB signals, the WHITE pulse and BLACK pulse are alternately input in the horizontal
blanking period of the respective signals.
For the Y/G signal, the voltage of the period during which the WHITE and BLACK pulses are input at IC100 (3/3) is set to 0
Vdc. For the PR signal, the WHITE and BLACK pulses are input at IC303 (1/3). The level of the WHITE pulse is set by the R–
Y PULSE LEVEL voltage while that of the BLACK pulse is set by the R–Y CLAMP OFFSET voltage. These two voltages are
switched by WHITE INSERT P at IC300 (3/3), and input to IC303 (1/3).
The same is performed for the PB signal.
4. Chroma Level Adjustment Circuit
The PR signal is level-adjusted by IC304 (gain control amplifier) to become the R–Y signal. The R–Y signal output from
IC304 is input to IC303 (2/3) and the voltage of the WHITE pulse is sample-held. At IC305 (1/2), this voltage and the
CHROMA voltage are compared to control the gain of IC304. As a result, the WHITE pulse voltage becomes equivalent to the
CHROMA voltage. Consequently, by varying the CHROMA voltage, the chroma level can be adjusted. The R–Y signal of the
IC304 output is also input to IC303 (3/3). In this IC, the voltage of the BLACK pulse is sample-held. This voltage and the
GND level are compared at IC305 (2/2) to control the DC bias of IC304. As a result, the pedestal level of the R–Y signal is
fixed at the GND level.
The same is performed for the PB signal.
5. Matrix Circuit
The Y signal, R–Y signal, and B–Y signal are matrixed to form the R signal, G signal, and B signal.
6-1
BVM-D32E1WA/D32E1WE/D32E1WU