Tektronix 7623, Инструкция по эксплуатации

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Circuit Description— 7623/R7623 Service
Logic stage is shown in Fig. 3-3. Only the components
essential to operation of this stage are shown in this
simplified schematic.
Transistor U99C is connected in the common-base
configuration to provide the output for this stage. The
collector load for U99C is provided by the Z-Axis Amplifier
in the CRT Circuit. Transistors U99D and U99E provide a
current-limiting action for this stage. The collector current
of U99D, represented by lt, is the maximum amount of
current that can flow in the circuit. The amount of this
current is determined by the relationship between the
Intensity Limit and Vertical Chopped Blanking. When both
of these inputs are HI the collector current of U99D, lt, is
maximum. This maximum level of I, is determined by
current I, in the base circuit of U99D established by
networks R76-R77 and R62-R63 into R110 and the
collector of U99E. During Vertical Chopped Blanking, the
respective input level goes LO. This shunts the current lj
from the base of U99D so the collector current of U99D,
lt , drops to minimum to blank the CRT display during
vertical trace switching.
The Intensity Limit function limits the output current
of this stage to protect the CRT phosphor whenever the
time-base unit is set to a slow sweep rate. For conditions
that do not require limiting, quiescent current is added to
Ij from the +15-volt supply through R76-R77. When the
time-base unit is set to a sweep rate which requires intensity
Fig. 3-3. Simplified schematic of Z-Axis Logic stage.
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