Section 4-608
T H EOR Y OF OPERATIO N
This section of the manual describes the circuitry in the 608 M onitor. 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 all major circuits are given in Section
8,
Diagrams and
Circuit Board Illustrations. Stages are outlined on the schematics with wide shaded lines; the stage names are in
shaded boxes. Refer to these schematics throughout the foll owing discussions for specific electrical values and
relationships.
N OTE
The Theory of Operation for available electrical options is located in Section
9,
Instrument
Options, at the rear of this manual.
B LOCK DIAG RAM
The fol lowing discussion is provided to aid in
understanding the overal l 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 I NPUT 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.
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
instrument.
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
fol lowing 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 l ocate the components mentioned in
the fol lowing discussions. The name of each stage,
given in a shaded box on the diagram, matches the
subheading in the discussion of that schematic
diagram.
V E RTICAL (Y) D EFLECTI O N
AMPLIFI E R
�
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,
showing each major stage of the Vertical
(Y)
Deflection Amplifier, is supe rimposed on the schematic
with wide shaded lines to conveniently locate the
components mentioned here. The stage names (given
as sub-headings in the fol lowing discussion) can be
found in the shaded boxes on diagram 1.
Y P R EAM PLl F I E R
Signals t o b e displayed are applied t o J101
(+Y
I NPUT). 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-Q134 and Q120B -Q230-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