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6. Vertical Output
This chassis employs an LA7837 for the vertical output circuit. It incorporates
a built-in ramp
generator circuit, constant vertical height function for 50/60Hz operation and pump-up cir-
cuit.
The vertical trigger pulse is driven by the negative polarity vertical sync pulse from the
IC201. The ramp generator circuit generates the vertical deflection sawtooth waveform. The
sawtooth waveform is generated by charging and discharging
the current in C513 connect-
ed to pin 6. This ramp signal drives the vertical drive circuit. In the first half of scanning peri-
od, a deflecting current is sent from pin 12 and passes through the following path;
VCC(24V) + D512 + pin 13 + pin 12 + DY + C515 + R518.
An electric charge is then stored in C515. In the last half of scanning period, the current
path is; C515 -+ DY +
pin 12 + pin ll(GND)
+ R518.
In this way, an increasing sawtooth waveform current flows directly to the DY to perform
electron beam deflection.
During the first half of the blanking period, the vertical ramp signal
suddenly turns off. Since there is no longer any current flowing into the DY, the magnetic
field collapses causing an induced current to flow as flows;
DY+
pin 12+
pin 11 +R518-C515+DY.
Once the magnetic field in DY has dissipated, the current path becomes;
Vcc+pin
8+pin9+C517+
pin 13~pin
12+
DY+C515+R518
and when the prescribed current value is reached. the vertical drive pulse turns on. This
completes one cycle.
VR51 O is for controlling the amount of feedback applied to pin 4 for the vertical size adjust-
ment.
IC501
VERT. 0UTPUT<LA7837>
IC201
lF/VIDEO/DEF.
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1213
2(
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scanning *rid
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Training
Manual
AC lChassis
-25-
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