Hitachi CM771ET, Руководство по обслуживанию

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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, C770
C777, are changed by Q767 Q771 and S77R, which provide 8 12 stages of
consonant conditions. The horizontal linearity coils L771 L772 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
From
MPU
+B E
HV
(85V)
SDA
HDRV
SEPA
I701
14
16
V.SYNC
H.CP
V.BLK
19
18
SCL
15
H.SYNC/Composite SYNC
17
MPU
H.SIZE CONTROL
OSCILLATOR
5 3 4 6 11
E / W
8
Buffer
Drive
12
13
Vertical
Output
I601
V.DY
RATER
1
HFLB
32
H.DF
Amp
V.DF
Amp
T751
Drive
Buffer
Detect
ERROR
E
HV
PWM
Module
Def
Out
H.Cent H.SIZE
PWM
H.DRIVER
f
H-V
H.SIZE
T751
Lin.
Coil Lin.
Coil
S.fig.
Cap. S.fig.
Cap.
Select Select
From MPU
From MPU
C770
C771~
C777
S77R
L771
L772
H.DY
Q765
+B (+200V)
Q767~
Q771
From MPU