Tektronix 442, Инструкция по эксплуатации

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Section 3—442 Service
THEORY OF OPERATION
GENERAL
This section describes circuitry used in the 442
Oscilloscope. The description begins with a discussion of
operation usingthe block diagram shown in Diagrams and
Circuit Board Illustrations (Section 7).
Next, each circuit is described in detail.
Refer to the schematic diagrams (in Section 7)
throughout the following discussions for specific elec­
trical values and relationships.
BLOCK DIAGRAM DESCRIPTION
The following discussion is provided to aid in un­
derstanding the overall concept of the 442 Oscilloscope
before individual circuits are discussed in detail.
VERTICAL INPUT
Signals to be displayed on the crt screen are applied to
either (or both) Channel 1 (X) and Channel 2 (Y) input
connectors. Input signals are amplified by Channel 1 or
Channel 2 preamplifier circuits as appropriate. Each
preamplifier circuit includes separate input coupling
switches, attenuators, gain switching, variable atten­
uators, balance, and gain adjustments.
A Trigger Pickoff circuit in each vertical channel
supplies a sample of the input signal to the Trigger Input
Amplifier via the Trigger Switching circuit and the
SOURCE switch.
When the SOURCE switch is in the X-Y position,
triggering is disabled and Channel 1 signals are con­
nected to the Horizontal Output Amplifier through the X
Buffer Amplifier. Channel 2 signals are connected through
regular Channel 2 vertical circuitry. Channel 1 provides X-
Axis deflection and Channel 2 provides Y-Axis deflection.
VERTICAL SWITCHING
The Vertical Mode switches select the desired channel
presentation and an appropriatetrigger signal. The output
of each Preamplifier is connected to the Delay Line Driver
through a corresponding Input Buffer and a Diode Gate.
The Diode Gates are controlled by the Vertical Switching
circuit (as determined by the Vertical Mode switch) to
select the channel(s) for display. An output from the
Vertical Switching circuit is connected through the Chop
Blanking Pulse Generator tothe Z Axis Amplifier to blank
switching transients in the CHOP mode. A sync pulse from
the sweep, via the Alternate Sync Pulse Amplifier,
switches the display between channels at the end of each
sweep in ALTernate mode. A DIFFerential function allows
a display of the difference between the two input signals
using circuitry that invertsthe Channel 2signal and adds it
algebraically to the Channel 1 signal.
VERTICAL AMPLIFIER
The vertical input signals gofrom the Delay Line Driver
through the Delay Line to the Vertical Output Amplifier.
The Delay Line provides approximately 140 ns delay in
vertical signal transfer. This allows the sweep generator
circuit time to initiate a sweep before the vertical signal
reaches the crt vertical deflection plates. One section of
the BEAM FINDER switch affects the Vertical Output
Amplifier circuitry. When the BEAM FINDER button is
pressed in, this section compresses the display vertically
to within the graticule area (another section affects the
Horizontal Amplifier circuitry and causes the display to
compress horizontally when the button is pressed in). This
aids in locating
off-screen displays. The vertical output
amplifier provides final amplification of the signal to drive
the crt vertical deflection plates.
TRIGGER
The Trigger circuits produce timed logic signals to
trigger the sweep. Trigger signals are selected by the
SOURCE switch from four different sources: From the
Composite Pick-off for COMP; from the Int Trigger
Switching and the Int Trigger Buffer Amplifier for CH
1/CH 2; from the secondary of T700 (line voltage) for LI NE;
and from the EXT input connector for the EXT trigger
REV A MAY 1980
3-1