Tektronix 608 monitor Instruction Manual page 25

Section 4—608
THEORY OF OPERATION
This section of the manual describes the circuitry in the 608 Monitor. The description begins with a discussion of
the instrument using the block diagram on Figure 4-1, and then continues in detail, showing the relationships
between the stages in each major circuit. Schematics of al! major circuits are given in Section 8, Diagrams and
Circuit Board I\!ustrations. Stages are outlined on the schematics with wide shaded lines; the stage names are in
shaded boxes. Refer to these schematics throughout the following discussions for specific electrical values and
relationships.
NOTE
The Theory of Operation for available electrical options is located in Section 9, Instrument
Options, at the rear of this manual.
BLOCK
The following discussion is provided to aid in
understanding the overall! concept of the 608 before
the individual circuits are discussed in detail. A basic
block diagram is shown in Figure 4-1.
Vertical and horizontal signals to be displayed on the
crt are supplied to the Deflection Amplifiers through
* the appropriate Y and X INPUT connectors. The
Deflection Amplifiers process the input signals and
provide push-pull outputs to drive the deflection plates
of the crt. Both Deflection Amplifiers contain position
and gain controls.
DIAGRAM
The Z-Axis Amplifier controls the display intensity by
providing a voltage to drive the crt control grid. Input
signals are applied to the Z INPUT connector.
The Dynamic Focus circuit provides focus correction
for the display when it is deflected from the crt
center. Thus, by varying the voltage to the crt focus
element, the Dynamic Focus circuit compensates for
geometric defocusing.
The High-Voltage and Low-Voltage Power Supplies
provide all the voltages necessary for operation of this
DETAILED CIRCUIT OPERATION
Complete schematic diagrams are provided in Section
8, Diagrams and Circuit Board Illustrations. The
numbers inside the diamond after a heading in the
following discussions refer to the schematic diagram
for that circuit. The schematic diagrams contain wide
shaded borders around the major stages of the circuits
to conveniently locate the components mentioned in
the following discussions. The name of each stage,
given in a shaded box on the diagram, matches the
subheading in the discussion of that schematic
VERTICAL (Y) DEFLECTION
AMPLIFIER <i>
The Vertical (Y) Deflection Amplifier processes the Y
input signals and provides final amplification to drive
the vertical deflection plates of the crt. A schematic
diagram of the Vertical (Y) Deflection Amplifier is
@
shown on diagram 1. A detailed block diagram,
Deflection Amplifier, is superimposed on the schematic
with wide shaded lines to conveniently locate the
components mentioned here. The stage names (given
as sub-headings in the following discussion) can be
Signals to be displayed are applied to J101 (+Y
INPUT). The Y Preamplifier employs a matched pair of
FETs to provide a high input impedance and
temperature stability. This stage consists of two
identical and inverting feedback amplifiers, Q120A-
Q130-0134 and Q120B-0230-Q234, which operate as
a paraphase amplifier. A push-pull signal is produced
at the collectors of Q134 and Q234. The FET gates
are diode-clamped on negative-going overdrive signals
to protect the field-effect transistors from excessive
4-1