Alternate B Sweep - Tektronix 2235A Instruction Manual

Theory of Operation
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2235A instruction
will again be reset, causing the TRIG'D LED to go out
and place a HI on the D input of U506A. A new sweep will
not be initiated until the SGL SWP button is again
pushed.
X-Y. In the X-Y mode of operation, the XY2(L) line is LO
which holds the input of U523B LO through CR518. The
output of U532B will hold U506A set and no sweeps can
be initiated.
ALTERNATE B SWEEP
The Alternate B Sweep circuitry, shown on Diagram 7,
produces a linear voltage ramp that is amplified by the
Horizontal Amplifier to provide the B Sweep horizontal
deflection on the crt. The Alternate B Sweep circuitry also
produces the sweep-switching signals that control the
display of the A and B Sweeps, and the gate signals
used by the Intensity and Z-Axis circuits to establish the
crt unblanking and intensity levels needed for producing
both the A Intensified and B Sweep displays.
The B Sweep ramp is enabled by the B Sweep Logic
circuit either immediately after the end of the established
delay time (Runs After Delay) or upon receipt of the first
trigger signal after the delay time has elapsed. This
delay time is a function of the B Delay Time Position
Comparator circuit and the A Sweep.
B Miller Sweep Generator
The B Miller Sweep Generator is composed of (2709,
Q710A, Q710B, Q712, and associated timing com-
ponents. This circuit produces the B Sweep and
functions in the same manner as the A Miller Sweep Gen-
erator; see the A Miller Sweep Generator section for a
description of circuitry operation. The output at the
collector of Q712 drives the Horizontal Amplifier and
Q643.
B Trigger Level Comparator and Schmitt
Trigger
The B Trigger Level Comparator and Schmitt Trigger are
contained in U605. This circuit determines both the trig-
ger level and slope at which the B triggering signal is pro-
duced. It functions in the same manner as the A Trigger
Level Comparator and Schmitt Trigger with the exclusion
of the TV trigger circuitry. See the A Trigger Level Com-
parator and Schmitt Trigger section for a description of
circuit operation. The
+
OUT terminal of U605 is directly
connected to the clock input of U670A to initiate the B
Sweep when the B trigger is utilized.
Runs After Delay
The Runs After Delay circuit allows the B Sweep Logicto
generate a B Sweep independently of any B Trigger
signals. In the Runs After Delay mode, B TRIGGER
LEVEL control R602 is rotated fully clockwise. This
biases off Q637 and places a LO on the collector.
Inverter U660D will then have a HI output with resistor
R640 providing positive feedback. This HI output reverse
biases CR626, so the state of U670A is determined by
the level at U660F pin 12.
If the B TRIGGER LEVEL control is not fully clockwise,
Q637 is biased on and the B Sweep is in the triggered
mode. The output of U660D will be LO which keeps the S
input of U670A LO, preventing the flip flop from being set
by the output of U660F.
Operation of the B Sweep Logic circuitry under both of
these conditions is described in the B Sweep Logic
discussion.
B Delay Time Position Comparator
The B Delay Time Position Comparator circuit compares
the amplitude of the A Sweep sawtooth output voltage to
the dc voltage level set by B DELAY TIME POSITION
potentiometer R9644. The output of the comparator is
used to initiate a B Sweep and to control the B Z-Axis
Logic circuit switching.
The inputs to the comparator, U655, arethe wipervoltage
of R9644 and the A Sweep voltage from the divider net-
work composed of R651, R652, and R653. Input voltage
ranges to the comparator are determined by VR645 and
R646 for the noninverting input and by R652 for the
inverting input. Delay Start potentiometer R646 is
adjusted in conjunction with potentiometer R652 to set
the B DELAY TIME POSITION dial calibration.
The output of the comparator is enabled or disabled by
the strobe signal connected to pin 6. When the
A-ONLY(L) signal is HI, the comparator is enabled.
When the A ONLY(L) signal is LO, the output of the com-
parator is ahigh impedance and therefore a HI is present
on pin 9 of U680C.
B Sweep Logic
The B Sweep Logic circuitry utilizes signals from the
associated B Sweep circuitry to generate control signals
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