Hitachi CL43WP910TAN, Service Manual

Page: 14 / 77

SYNC Signal Processor - uPC1885A
Vertical Deflection & Geometry Controls.
The drive circuit for the vertical and E-W deflection circuits are generated by means of a
vertical divider which gets its clock from the line oscillator. The divider is synchronised
b
y the incoming vertical pulse, generated by the input processor or the feature box.
The vertical drive circuit outputs vertical sawtooth wave whose amplitude is set by
internal VCA circuit and on which S and C shaped correction wave are superimposed.
Center voltage of vertical sawtooth wave is changed by vertical position DAC. The
outputs must be DC coupled to the vertical output stage. The vertical geometry can be
a
djusted by I2C control via the service menu.
Horizontal Synchronisation & Drive Circuit.
The horizontal drive signal is obtained from an internal VCO which is running at a
frequency of 500KHz. The internal VCO is synchronised to the incoming H.SYNC pulse
by means of a PLL with an internal time constant. The horizontal drive signal generated
by means of a control loop which compares the phase of the reference signal from the
in
ternal VCO with the flyblack pulse. The time constant loop is internal.
Vertical A
mplifier
– LA7841L
The LA7841L is vertical deflection output amplifier.
Pin 5, vertical sawtooth wave is taken with DC from pin 8 of uPC1885A.
Pin 2 outputs the vertical output voltage, and pin 7 outputs the vertical blanking pulse.
B
lock Diagram of LA7841 is as shown below.
THERMAL PUMP UP
PROTECTION
-
AMP
+
1 2 3 4 5 6 7
F
ig. 5 Block Diagram of LA7841L