Panasonic EURO 4 Chassis, Техническое руководство

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9.4. Vertical Output Stage
To drive the vertical output stage, the drive pulse is
output from the VDP
IC601 pin 31 and fed to the
vertical output stage IC451 pin 5.
This vertical output IC IC451 consists of an
operational amplifier to which the vertical drive pulse
in the form of a sawtooth is passed, the results of
which are output via pin 2.
The gain of the internal op-amp. is controlled by the
negative feedback pulse which is fed via R454
connected between pin 2 and pin 5.
IC451 also contains a pump-up circuit which is used
to provide a switching voltage for the vertical flyback
period. This is required as the energy requirement of
the vertical output stage is highest during flyback, as
the electron beam has to be passed rapidly from the
bottom right hand corner of the screen to the top left
corner of the screen.
This brief additional energy requirement is met by
doubling the supply voltage available to the output
stage.
During vertical sweep, the bootstrap capacitor C456
is charged up to almost supply voltage via D454.
The output of the pump-up generator pin 7,
IC451 is
at this moment at ground potential.
As a result of the DC displacement at the negative
pole of capacitor C456 (rising to the supply voltage),
build up of the supply voltage for the output stage at
pin 3 rises to almost twice the supply voltage. At the
same time, D454 is reverse biased and thus
prevents discharge of C456 into the supply line.
9.4.1.Vertical Protection
The output pin, pin 2 of IC451 which is directly
connected to the deflection coil is monitored by the
protection input of the VDP
IC601 .
Here a vertical flyback pulse is fed to pin 11 of the
VDP
IC601 , which is used to signal a fault (as
described in section 17.10.3. ).
When a fault is detected the RGB signals are
blanked preventing any damage of the CRT.