SECTION 3
CIRCUIT DESCRIPTION
434
Change inform ation, if any, affecting this section w ill be found at the rear o f the manual.
Introduction
This section of the manual contains a description of the
circuitry used in the 434 Oscilloscope. The description
begins w ith a discussion of the instrument using the basic
block diagram shown in Fig. 3-1. Then, each circuit is
described in detail, using a detailed block diagram to show
the interconnections between the stages in each major
circuit and the relationship of the front-panel controls to
the individual stages.
A complete block diagram is located in the Diagrams
section at the rear of this manual. This block diagram shows
the overall relationship between all of the circuits. Com
plete schematics of each circuit are also given in the
Diagrams section. Refer to these diagrams throughout the
follow ing circuit description for electrical values and
relationship.
BLOCK DIAGRAM
General
The follow ing discussion is provided to aid in under
standing the overall concept of the 434 before the indi
vidual circuits are discussed in detail. A basic block diagram
of the 434 is shown in Fig. 3-1. Only the basic inter
connections between the individual blocks are shown on
this diagram. Each block represents a major circuit w ith in
this instrument. The number on each block refers to the
complete circuit diagram which is located at the rear of this
manual.
Signals to be displayed on the CRT are applied to the
CH 1 and/or CH 2 input connectors. The input signals are
then amplified by the Channel 1 Input Amp and Preamp
and/or the Channel 2 Input Am p and Preamp circuits. Each
vertical circuit includes separate vertical deflection factor,
position, input coupling, gain, variable attenuation, and
balance controls. A sample of the Channel 1 signal is
supplied to the Trigger Pickoff circuit. The Channel 2
Preamp circuit contains an invert feature to invert the
Channel 2 signal as displayed on the CRT. The output of
both Vertical Preamp circuits is connected to the Channel
Switch circuit. This circuit selects the channel(s) to be
displayed. An output signal from this circuit is connected
to the 2 Axis A m plifier circuit to blank out the between-
channel switching transients when in the chopped mode of
operation. A sample of the signal present in the Channel
Switch circuit is supplied to the Trigger Pickoff circuit.
The output of the Channel Switch circuit is connected
to the Vertical O utput A m plifier through the Delay Line.
The Vertical O utput A m plifier circuit provides the final
am plification fo r the signal before it is connected to the
vertical deflection plates of the CRT. This circuit includes
the BEAM FINDER switch which compresses the vertical
and horizontal deflection within the viewing area to aid in
locating an off-screen display.
The Trigger P ickoff and Generator circuit selects a
trigger signal (determined by the TRIGGER SOURCE
switch) and produces an o utput pulse which initiates the
sweep signal produced by the Sweep Generator circuit. The
internal trigger signal is selected from the Channel 1 circuit
or the Channel Switch circuit. A sample of the line voltage
applied to the instrument or an external signal applied to
the EXT TRIG input connector can also be used to gener
ate a sweep-starting pulse. The trigger circuit contains level,
slope, coupling, and source controls.
The Sweep Generator circuit produces a linear sawtooth
output signal when initiated by the Trigger Generator
circuit. The slope of the sawtooth produced by the Sweep
Generator circuit is controlled by the T IM E/D IV switch.
The operating mode of the Sweep Generator circuit is
controlled by the sweep MODE switch. In the AUTO mode
of operation, the absence of an adequate trigger signal
causes the sweep to free run. In the NORM mode, a hori
zontal sweep is presented only when correctly triggered by
an adequate trigger signal. The SINGLE SWEEP mode of
operation allows one (and only one) sweep to be initiated
after the circuit is reset w ith the RESET button. The Sweep
Generator also produces an unblanking gate signal to
unblank the CRT so the display can be presented. This gate
signal is coincident w ith the sawtooth produced by the
Sweep Generator circuit. A dditionally, the Sweep Genera
tor circuit produces an alternate trace sync pulse which is
connected to the Channel Switch circuit. This pulse
switches the display between channels at the end of each
sweep when in the A LT mode of operation.
The output of the Sweep Generator circuit is amplified
by the Horizontal A m plifier circuit to produce horizontal
deflection fo r the CRT in all positions o f the T IM E /D IV
switch except EXT HORIZ. This circuit contains a six-
position magnifier switch to increase the sweep rate up to a
maximum of 50 times. Other horizontal deflection signals
can be connected to the Horizontal A m plifier by using the
®
3-1
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