Tektronix 323, Инструкция по эксплуатации

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SECTION 3
CIRCUIT DESCRIPTION
Type 323
Change information, if any, affecting this section will be found at the
rear of the manual.
Introduction
Block diagram and detailed descriptions of the Type 323
Oscilloscope circuitry are contained in this section. The
block diagrams and schematics contained in the rear of
this manual are used in conjunction with the descriptions.
Numbers which are contained in diamond-shaped outlines
appear in conjunction with the schematic names. These
numbers are used extensively on the schematics for cross-
referencing and are therefore contained in a diamond­
shaped outline for quick recognition.
Simplified drawings are provided where necessary for
effective circuit explanations. No attempt is made to ex­
plain basic operations of components except for those that
are not considered generally known. Additional information
regarding components is included in the Maintenance sec­
tion of this manual.
BLOCK DIAGRAM DESCRIPTION
Refer to the block diagram contained in the Diagrams
section. Operation with an internal sweep will be discussed
first.
Infernal battery, external DC, or AC powered operation
can be selected at the Power Pack. During AC operation,
the AC power input is full-wave rectified and applied to
battery charger circuits which supply power to the external
batteries and the oscilloscope circuits. During EXT DC op­
eration the battery and battery charging circuit are by­
passed and the applied voltage goes directly to the POWER
switch.
In all modes of operation, a DC voltage is received by
the Power Regulator, which employs a blocking oscillator
and flyback-type transformer to develop the voltages which
are used throughout the Oscilloscope. This includes CRT
filament supply and high voltage.
When internal sweep operation is selected, the Trigger
Generator develops triggers in response to any of three
sources as selected by the operator: trigger multivibrator,
vertical signal, or externally applied triggering signal. When
the vertical signal or the EXT TRIG input is selected, the
Comparator Amplifier causes the Trigger Multivibrator to
generate a trigger each time the input signal passes through
a specific voltage as determined by the Compartor Ampli­
fier. When AUTO triggering is selected, the Trigger Multi­
vibrator free-runs, providing a continuous succession of trig­
gers. Whenver either a vertical signal or external trig­
gering signal is present and has a higher frequency than
the multivibrator's free-running rate, the multivibrator no
longer free-runs but becomes slaved to the triggering signal.
The Trigger Multivibrator output enables a Sweep Gate
circuit. This causes the Sweep Generator circuit to develop
a linear sawtooth voltage, which drives the Horizontal Am­
plifier. The Horizontal Amplifier increases the amplitude of
the sawtooth voltage as necessary to provide slightly more
than ten division of horizontal deflection when the voltage
reaches its peak.
When the sawtooth voltage out of the Sweep Generator
rises sufficiently positive to provide full trace deflection, it
disables the Sweep Gate and the sweep voltage returns to
its reference value. The Holdoff Circuit prevents triggers
from reaching the Sweep Gate during sweep time, and con­
tinues to block them until enough time has elapsed after
sweep time for the circuits to return to their quiescent values.
This ensures that each sweep will start from the same point
at the left edge of the graticule.
Deflection blanking is used in the CRT to prevent the
electron beam from striking the CRT face during retrace
and holdoff time. The Sweep Gate output causes the Un­
blanking Amplifier to apply +100 V to an unblanking de­
flection plate during sweep time. This cancels the effect
of the +100 V which continuously exists on an opposing
deflection blanking plate, permitting the horizontal (and
vertical) deflection plates to control beam position on the
face of the CRT. The CRT beam can be blanked at any time
by application of an external blanking signal of at least
+ 5 V to EXT BLANK jack J350.
When a signal is applied to the VERT INPUT, it passes
through an attenuator which is controlled by the VOLTS/
DIV switch. The signal (or a portion of it as determined
by the switch setting) is applied to the Vertical Preamp
where it is amplified and converted to a push-pull signal.
It is then amplified by the Vertical Output Amplifier which
applies the signal to the CRT vertical deflection plates. The
vertical signal applied to the upper deflection plate is also
applied to the Trigger Generator circuit. This slaves the
trigger and sweep generator to the input signal frequency,
thereby permitting a stable display.
Alternate Modes of Operation
5 DIV CAL. The gain and the overall operation of the
oscilloscope can be checked by switching the VOLTS/DIV
switch to a 5 DIV CAL position. At that time a square wave
is accepted from an internal Calibrator. The appearance
of a 5 division square wave on the CRT is indicative of
proper operation. Its amplitude is sufficiently accurate to
permit gain calibration. A 0.5-V square wave signal from
the Calibrator is always available at a CAL OUT jack for
purposes such as calibrating an attenuator probe.
EXT HORIZ. The horizontal beam deflection can be con­
trolled by an externally applied signal when the TIME/DIV
switch is placed in the EXT HORIZ position and the Trig/
Horiz Coupling switch is in an EXT TRIG OR HORIZ posi-
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