Horizontal Deflection Circuit - Hitachi H972 Service Manual

3. Horizontal Deflection and High Voltage Regulation Circuit

3.1 Horizontal Deflection Circuit

The purpose of the horizontal deflection circuit is to cause the CRT electron beam to be scanned horizontally by driving
a current through the deflection yoke, synchronized by the H sync pulse. The circuit consists of an AFC circuit, made up
of an H phase locked loop and VCO (voltage controlled oscillator), and the deflection output.
The H.sync. signal is input to I701 where it is delayed and then input to a phase detector. The phase locked loop (I701)
also accepts input from a saw tooth waveform which is provided by the deflection feedback (flyback pulse) through the
R707. The output of the phase detector creates an error voltage between the feedback pulse and the input pulse and is
then fed to the VCO after processing by an AFC Filter.
If the oscillator frequency deviates more than 4% of H.SYNC, PLL1 (I701) goes into search mode and HUNLOCK (I701)
changes to "H". The minimum horizontal frequency is determined by the capacitor at C706 and R704. Horizontal
frequency range is determined by R705. H.SIZE, S.PIN and Trapezium are controlled by PWM circuit (Q801). The
output pulse from the VCO is fed to the pre-drive and then output from I701 to the drive buffer Q701 / Q702. The
pre-drive circuit within I701 is controlled by duty cycle by the internal circuit.
In case of no sync signals supplied or excessive frequency change, such as a signal timing change, HUNLOCK once
changes to "H", and PWM circuit (Q801) output is stopped.
The deflection circuit of the DJ72 chassis has been separated from the high voltage regulation circuit to provide
improved H linearity performance by utilizing the consonant conditions of the horizontal beam current characteristics.
The S-consonant capacitors, C770C777, are changed by Q767Q771 and S77R, which provide 812 stages of
consonant conditions. The horizontal linearity coils L771L772 are changed by S77R to provide two stages of H
Linearity conditions.
The H.DEF +B voltage chopper power supply parabolically modulates the H.DEF +B voltage of the deflection circuit,
based on the horizontal frequency, to provide a frequency - dependent voltage of between 42.5V and 160V to the
deflection circuit.
FIG. 8 HORIZONTAL DEFLECTION CIRCUIT
HFLB
V.SYNC
H.CP SEPA
RATER
V.BLK
SDA
From MPU
SCL
H.SYNC/Composite SYNC
MPU
+B (+200V)
I701
1
14
16
19
18
15
17
5 3 4 6 11
E / W
H.SIZE CONTROL
OSCILLATOR
Drive
Buffer
H.SIZE
PWM
H.DF
32
Amp
V.DF
Amp
I601
12
Vertical
13
Output
8
Drive
HDRV
Buffer
f
From
H-V
H.DRIVER
MPU
H.SIZE
Q765
Def
Out
H.Cent
C771~
C777
Q767~
Q771

10

T751
T751
+B E (85V)
HV
V.DY
E PWM
HV
Module
H.DY
L771
L772
Lin. Lin.
Coil Coil
S77R
C770
S.fig. S.fig.
Cap. Cap.
Select
From MPU
ERROR
Detect
Select
From MPU