Vertical Deflection Circuit - Hitachi H972 Service Manual

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4. Vertical Deflection Circuit

The purpose of the vertical deflection circuit is to cause the CRT electron beam to be scanned vertically by driving a
current through the deflection yoke, synchronized by the V sync pulse. V sync is input to the V oscillator circuit, I701,
generating the vertical saw tooth wave. The vertical saw tooth wave is fed to I601 to be amplified of I601 to drive the
vertical deflection yoke.
The feedback circuit inside I601 works such that the differential voltage between pin9 and pin4 equals zero. The
differential input current is compared with the feedback current, and the differential drives the output amplifiers. By
varying resistor R612 or R619 one can set the desired deflection current.
The picture can be shifted in vertical direction by making a DC-offset current through the coil. DC-offset current through
the coil is controlled by the differential input current from I701.
I601 uses an external flyback supply voltage, which is connected to pin7. The signal from the I601 8pin output is used
for protection. The guard output is also activated during thermal shutdown i.e. when Tj>=160
of range.
FIG. 11 VERTICAL DEFLECTION CIRCUIT
I701
V.OUT
14
V.SYNC
V.Lin
V.Lin balance
From MPU
V.Position
SDA
19
SCL
18
I601
GUARD
CIRCUIT
1
IN A
13
INPUT
PROTEC
STAGE
2
IN B
12
GND
V
V
V.BLK
P
FB
+
C609
+
C613
8
3
5
FLYBACK
GENERATOR
AMPLIFIER
A
TION
AMPLIFIER
B
 13 
o
C, and feedback loop out
7
6
OUT A
C610
R620
9
FEEDB
R619
4
OUT B
R611
V.DY
R612

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