G1 Board; B Board - Sony BVM-D14H1E Maintenance Manual

6-2. G1 Board

The G1 board is the standby regulator circuit that supplies
the standby power (STBY5V) for the control system
devices (such as CPU).
The standby regulator consists mainly of IC601, IC1602,
PH601, T1601 and D1606. IC1601 has the built-in
switching FET, the PWM controller and protection circuit.
The control terminal of IC1601 receives the control signal
from IC1602 that performs the constant voltage control
over the STBY5V line through the isolator PH601. The
internal FET inside IC1601 is PWM-switched by the
control signal so that the STBY5V output from the second-
ary winding of T1601 is stabilized.
1. Over-Voltage Protection and Over-Current
Protection Circuit
The STBY5V line of the standby power supply have the
over-voltage protection circuit that protects the power
supply and the loads when an abnormality occurs in the
voltage feedback system.
When the over-voltage is detected, the "LOW" signal is set
to the control terminal of the latch circuit through the
isolator PH602 so that the power supply is stopped by the
latch circuit consisting of Q606 and Q607.
This protection circuit is released wen the input power is
turned off that discharges the C615 voltage of the G board.
When an over-current is detected in the STBY5V line, the
micro-fuse F1603 blows.
6-4

6-3. 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 in the Y/PB/PR signal is
being input.
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 Y-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 by 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 controls the DC bias of the R-
signal amplifier (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.
BVM-D14H1U/D14H5U/D14H1E/D14H5E/D14H1A/D14H5A