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The horizontal deflection circuit is separated from
high voltage circuit which generates the anode voltage
for the CRT.
The upper limits for the beam current and the high
voltage are determined in Safety Circuit considering
the X-'RADIATION LIMIT CURVE of CRT.
The characteristics of the components employed to
generate the high voltage have no effect on the upper
limit.
Excessive high voltage is detected through the dividing
resistors and is fed to Safety Circuit II.
Safety Circuits II operate based on the derived voltage
generated from the resistor divider.
The voltage across the capacitor C323 which is
proportional to the high voltage is fed to Safety
Circuits II through R318 and VR302.
Safety Circuit II contains a comparator, IC302
which triggers silicon controlled rectifier
(SCR),
TH301 when the sample voltage fed to IC302 pin 2
exceeds the fixed voltage at pin 3 generated by R323
and R325.
The voltage at pin 3 is normally greater
than the potential at pin
2,
therefore, the voltage at
pin 2 will increase higher than voltage at pin 3 when
the high voltage exceed limiting level 29 kV, and
IC302 turns on to activate SCR, TH30l.
TH301 pulls
down the potential of ICSOl, pin 1 and drive signal
for high voltage circuit is interrupted completely.
3-16
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