Sony BVM-D14H1E Maintenance Manual page 76

3. Over-Voltage Protection and Over-Current
Protection Circuit
The +135 V voltage line of the main power supply has the
over-voltage protection circuit and the over-current
protection circuit that protect the power supply circuit and
the loads when an abnormality occurs in the respective
loads and in the voltage feedback system.
When an over-current occurs, the latch circuit consisting of
Q616 and Q617 is turned on so that the VCC power to
IC601 and IC602 is turned off through the isolator PH604
to stop operation of the main power supply circuit.
This protection circuit is released when the input power to
the main power supply circuit is turned off once or when
the standby mode is selected.
Deflection and High Voltage Circuit
1. Sync Signal and Deflection Signal Processing
Circuit
The horizontal and vertical sync signals that are input from
CN501 (pins-1/-2) are sent to the H/V DELAY timing
circuit consisting of IC510, IC522, IC509 and IC526. The
H/V DELAY timing circuit outputs the sync signals that
have the same phase as those of the input signal during
normal operation. However, during the H/V DELAY
mode, it outputs the delayed sync signals to which delay is
given by IC509 and IC510. The output sync signals are
processed of the waveforms by IC503 and are sent to the
deflection signal processor IC507.
The deflection signal processor IC507 outputs the various
signals that are required for deflection, such as horizontal
drive circuit, parabola signal for dynamic focusing,
parabola signal for picture distortion correction, vertical
drive signal and H/V blanking signals. The output signals
are controlled directly by the microprocessor in the MA
board through I2C bus.
The horizontal free-running frequency is set for about 18
kHz. The pull-in range of the input signal frequency is
from 15 kHz to 45 kHz.
The deflection signal processor IC507 has the built-in
protector for X-ray protection. When its pin-15 is raised to
8 V or higher, the X-ray protection circuit starts working to
stop the horizontal and vertical outputs. The X-ray
protector circuit can be reset by turning off the main power
once then back on, or by entering the standby mode.
There can be a case that the monitor receives the non-
standard TV signal such as the output signal from VTR. In
order to reduce the skew effect on screen caused by
irregular timing of the input sync signal, the PLL circuit
inside the IC507 is stopped during the vertical blanking
period.
6-2
This function is effective when the horizontal frequency of
the input signal is 15 kHz (NTSC and PAL).
Because this circuit produces an ill effect when the stan-
dard TV signal is input, use or not-use of this circuit can be
selected from the on-screen menu.
2. PWM Control Circuit for +B Power Voltages
for Horizontal Deflection and of High Voltage
The PWM control circuit for +B power voltage consists of
IC515 and its peripheral circuit. The horizontal drive
signal that is output from IC507 pin-21 is used as the
PWM trigger signal.
The PWM control for horizontal deflection system is
performed by inputting the deflection distortion correction
signal that is output from IC507 pin-31 to which the H.
size control DC voltage super-imposed, to IC515 pin-8.
On the other hand, the horizontal signal that is fed back
from the horizontal output circuit is inputted to IC515 pin-
7. These two input signals are compared and the error
signal between them, that is the PWM control signal is
output from IC515 pin-11. The PWM control output
signal is sent to the +B regulator circuit consisting of
Q2503 and its peripheral circuit that control the H. size and
the deflection distortion correction.
The PWM control for the high voltage circuit is performed
by inputting the reference signal generated by IC519, to
IC515 pin-16 that is compared with the FBT high voltage
detected voltage that is input to IC515 pin-17. The error
signal between them, that is the PWM control signal is
output from IC515 pin-13. The PWM control output
signal is sent to the +B regulator circuit consisting of Q514
and its peripheral circuit that control the high voltage to be
supplied to CRT.
The PWM control signal that is output from IC515 re-
ceives the DTC (Dead Time Control) in order to protect
the horizontal output circuit and the high voltage output
circuit from damage caused by the sharp change of fre-
quency of the input video signal. The DTC circuit works
as follows. When frequency of the input sync signal is
changed, the unlock signal that is output from IC507 pin-
37 is sent to IC507 pin-6 as the DTC signal input via the
switches Q523 and Q504, so that the PWM is controlled to
decrease the +B regulator output voltages to be supplied to
the horizontal and high voltage systems.
3. Horizontal Output Circuit
The horizontal drive signal that is output form IC507 pin-
21 is amplified by the horizontal drive circuit consisting of
Q2501, Q2502, Q2505 and their peripheral circuit. The
horizontal drive signal then drives T2502 (HDT) and
Q2508 (H. OUT). The H. pulse is induced by the reso-
nance between the capacitors C2528, C2530, C2531 and
theH. winding impedance.
BVM-D14H1U/D14H5U/D14H1E/D14H5E/D14H1A/D14H5A