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Theory of Operation—2213 Service
input current in a manner that complements the nonlinear
triode characteristics of the crt. This output voltage is
applied to the Z-Axis Am plifier via the Z-Axis Gating
circuit. The Intens Level signal is also applied to the Focus
circuit (Diagram 9) fo r use in focus tracking o f the intensity
level changes.
The intensity o f the display is allowed to reduce to zero
through the action o f CR809, VR809, and R809. W ithout
this circuit, the Auto Intensity circuit would not allow the
intensity to go to zero when the AUTO INTENSITY
control is set to minimum intensity.
Z-Axis Amplifier
The Z-Axis Am plifier controls the crt intensity level
via several input-signal sources. The effect o f these input
signals is either to increase or decrease trace intensity or to
completely blank portions o f the display. The Z-Drive
signal current and the input current from the Z-AXIS
INPUT connector (if in use) are summed at the emitter of
common-base amplifier transistor Q841. The algebraic sum
o f these signals determines the collector current o f Q841.
Input transistor Q841 provides a low-impedance termina
tion for the input signals and isolates the signal sources from
following stages of the Z-Axis Am plifier.
Signal current from Q841 flows through CR844 and
develops a signal voltage drop across R844. Increasing
current through Q841 reduces the forward bias o f Q844,
thereby reducing the current through Q844. This action
causes the collector voltage o f Q844 to go more negative
(toward the —8.6 V supply) and increases the forward bias
on em itter-follower Q845. As em itter current o f Q845
increases, negative-going voltage developed across R847 is
applied to the bases o f complementary-pair output tran
sistors Q847 and Q850. Positive transistions o f the Z-Axis
signal are coupled to the base o f Q850 via C852. The fast-
rise transitions are amplified by Q850 to speed up the
response time. For negative transitions o f the Z-Axis signal,
as well as fo r dc and low-frequency signal components,
Q847 acts as the amplifier, w ith Q850 supplying the
current.
Diode CR856 prevents the Z-Axis output signal from
going negative, and neon lamps DS854 and DS856 provide
protection to the Z-Axis Am plifier in the event o f high-
voltage arcing in the crt.
The amplifier gain w ith respect to the Z-Drive current is
set to about 10 by the negative feedback supplied from the
collectors o f Q847 and Q850 to the base of Q845 via
feedback resistor R846. The gain w ith respect to the
external Z-Axis Input signal is held to about three by R801,
R802, and R803 in series w ith the external input signal.
Diodes CR801 and CR802 provide protection fo r the
Z-Axis Am plifier in case o f an accidental application o f
excessive signal amplitude to the Z-AXIS INPUT connector.
When CHOP VER TIC AL MODE is selected, the Chop
Blank signal is applied to the collector o f Q841 during the
display switching time. Signal current is shunted away from
CR844, and the forward bias o f Q844 increases to the
blanking level. When blanked, the output o f the Z-Axis
A m plifier drops to about +10 V, and the crt beam current
is reduced to below viewing intensity to eliminate chop
switching transients from the display.
For an X-Y display, the Sweep Z-Drive signal current is
switched off. When the X Y signal is LO, CR837 is forward
biased and Intens Level current flows through R837 to
Z-Axis A m plifier transistor Q841 to establish the display
intensity.
The last input to the Z-Axis A m plifier is the Beam Find
current. Normally, BEAM FIND switch S390 is closed, and
—8.6 V is supplied to the base bias network o f Q841 and
Q844. When the BEAM FIND switch is opened, the —8.6 V
is removed, and the bias voltage becomes more positive.
Transistor Q841 becomes more forward biased while Q844
becomes much less forward biased. The current through
Q844 is reduced, and the base bias voltage o f Q845 is
thereby increased. The output o f Q845 then goes to a level
th at produces a fixed, predetermined Z-Axis o utput signal
level. Thus neither the AUTO INTENSITY control nor the
Z-Drive signal have any control over the intensity level
o f the crt display whenever the BEAM FIND push button
is pressed in, and a bright trace (or dot if no sweep is
present) w ill be displayed.
HORIZONTAL
The Horizontal A m plifier circuit, shown on Diagram 7,
provides the output signals that drive the horizontal crt
deflection plates. Signals applied to the Horizontal Pre
am plifier can come from either the M iller Sweep Generator
(for sweep deflection) or from the X Y Am plifier (when
X-Y display mode is selected). See Figure 3-7 fo r a detailed
block diagram o f the Horizontal A m plifier circuit.
The Horizontal POSITION control, X I 0 magnifier
circuitry, and the horizontal portion o f the beam finder
circuitry are also contained in the Horizontal A m plifier
circuit.
Horizontal Preamplifier
The sum o f the sweep and positioning current is applied
to the input o f one side o f a differential amplifier
composed o f Q730 and Q731. For all conditions other than
3 -2 0
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Содержание 2213
Страница 1: ...Ttektronix 2213 OSCILLOSCOPE SERVICE IN S T R U C T IO N M A N U A L ...
Страница 9: ...2213 Service 3827 01 viii The 2213 Oscilloscope ...
Страница 30: ...Theory of Operation 2213 Service 3 3 Figure 3 1 Basic block diagram of the 2213 Oscilloscope ...
Страница 67: ...Adjustment Procedure 2213 Service 5 2 ...
Страница 139: ...Figure 9 4 2213 block diagram S105 ...
Страница 140: ...a o m 7 x C O o z CHANNEL SWITCH AND VERTICAL OUTPUT ...
Страница 141: ...2213 Service ...
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Страница 146: ...2213 3827 20 R V FB 4982 C 4 ...
Страница 147: ...S90I 4 5 ...
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Страница 190: ...i _____H M N XY AMPLIFIER HORIZ OUTPUT ...
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